Title: Exotic Intruders

Author: Joan Druett

Publication details: Heinemann, 1983, Auckland

Digital publication kindly authorised by: Joan Druett

Part of: New Zealand Texts Collection

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Exotic Intruders

Chapter Nine — The extermination squad

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Chapter Nine
The extermination squad

Do you think you could bring out some ferrets or weasels, because rats are very numerous. You might have them in a small box in your cabin!

William Deans, writing to John Deans, April 2, 1842

By the 1890s the controversy over the importation of animals into New Zealand was well alight. Everyone had opinions on what should or should not have been brought in, in the past; and what should or should not be brought in, in the future. 'If the sparrow, the greenfinch and the blackbird could be eliminated,' pronounced Mr Bathgate to the Otago Institute, 'I do not think we should have much to complain of in the work done by the societies.' He went on to recommend the importation of butcher-birds. Reasonably happy about the introduction of the rabbit, he said 'he has afforded employment to large numbers of our population,' but that 'his presence is . . . responsible for the introduction of the stoats and weasels by the Central Government, which must be classed as one of the grave errors in acclimatisation.' At about the same time Taylor White, in Hawkes Bay, was complaining, 'I am sorry to see from newspaper reports that the members of the Hawkes Bay Rabbit Board have decided against the importation of weasels.' He asked whether the members were worried that the weasel would turn to other food when the rabbits were wiped out, and recommended that they look back to the situation in Britain. 'If the weasel was left unchecked to increase at will, why did it not exterminate the rabbit, then the game-birds, then the sheep, then cattle and horses, till at last man had finally to succumb before this energetic little bloodsucker?'

The public on the whole, and the sheep farmers in particular, were on Mr White's side. Animals such as rabbits had multiplied and became a pest, they argued, because man had neglected to bring out their natural enemies as well. As Thomson said later, 'Nearly all our introduced animals have been brought from lands where the struggle for existence is very keen, and where natural enemies abound. In their new home they page 168 have been set free from these trammels, and the enemies have been left behind.'

The choice, once the collective public mind had been more or less made up, was, which natural enemies? The Hawkes Bay Herald, in 1886, reported a local suggestion, following the Parliamentary Enquiry into the Rabbit Nuisance, that the Government should import large numbers of weasels, stoats and pine martens to deal with the rabbits. In August that same year a Captain Corbett advocated the importation of badgers instead of stoats and weasels. One authority actually proposed to introduce Arctic foxes, because the fur would be a fringe benefit of great value. When it was pointed out to this enterprising gentleman that the foxes might prefer lamb to rabbit, he replied with aplomb that as Arctic foxes don't eat lambs in their native habitat, it was unlikely that they would take to eating them in this country. Mr Bayly, the Superintending Rabbit Inspector, came down firmly in his 1883 report in favour of stoats and weasels. He had had a very unfortunate experience with ferrets the previous year. In March 1882 a shipment of 1 217 ferrets had been shipped from England. The animals had been collected by a Liverpool animal fancier called Cross, who shipped the ferrets out with live pigeons, biscuits, condensed milk, maize and sacks of hay. The corn was to feed the pigeons and the pigeons were to feed the ferrets. The hay was for the hutch bedding, and the biscuits and condensed milk were in case the pigeons ran short. A wry footnote is that at about the same time the same gentleman, Mr Cross, was involved in shipping rabbits to Canada.

What happened to the ferrets is not clear. Bayly said, 'The importation of ferrets has not been attended with the success that was anticipated, disease during the
Two ferrets or fitches. One is the original albino colouring developed by the Romans many centuries ago; the other is the darker colouring found more usually in the animal in New Zealand. The fur of both is prized, but the albino has the advantage of easy dyeing for fashion colours.

Two ferrets or fitches. One is the original albino colouring developed by the Romans many centuries ago; the other is the darker colouring found more usually in the animal in New Zealand. The fur of both is prized, but the albino has the advantage of easy dyeing for fashion colours.

page 169 voyage having carried off, in many instances, the whole of a shipment.' The fact is, that of that consignment of over a thousand ferrets, one hundred and seventy-eight arrived alive. Ferrets are inbred creatures, having been domesticated since Roman times. A ferret sickening with distemper may have been included in the shipment. Or the animals may have succumbed to pasteurellosis, known today as 'shipping fever'. The circumstances are probably never to be known, but the misery in the hutches can be left to the imagination.

Mr Bayly also shipped 241 ferrets from Melbourne, a much more suitable choice of place. Ferrets in Melbourne provided a rather barbaric sport: rats were released into a pit, and then a ferret was put in amongst them for three minutes. It was rather like the Elizabethan sport of bear-baiting, or cock-fighting in modern Indonesia. The winning ferret was the one that killed the most rats in the allotted time. This was a very popular sport in Melbourne, which had several of these pits. Of the Melbourne ferrets, 198 arrived alive. However the greatest success with ferrets was found in the depots at Waimate, Masterton and Christchurch, where ferrets were bred in captivity. One hundred and twenty-two ferrets were born at these depots in 1882— however it must be admitted that many of these died of distemper. Understandably, therefore, Mr Bayly, while admitting that 'the general impression (is) that the ferret is doing good work,' said that 'to be thoroughly serviceable a hardier animal is required . . . Inquiries tend to show that the stoat and weasel, if they can possibly be imported, would be the best agents of destruction.'

Ferrets, stoats and weasels belong to the animal family known as Mustelidae—the mustelids. The mustelids make up a big tribe, with members native to every country except Australia, Madagascar—and New Zealand. They are characterised by their small size, their agility, their blood-thirstiness, and their great courage. They hunt and kill rabbits and even hares, they catch ground-nesting birds, including pheasants and partridges, and they redeem themselves somewhat by destroying large numbers of rats and mice.

Rabbit-hunters, from times dating back to the ancient Romans, developed the modern ferret by generations of selective breeding from the wild polecat. The polecat is a big, rank animal, with a dark-brown coat and a pale yellow stomach. It is most unpopular: the name 'pole-cat' is derived from the French 'poule-chat', or 'chicken-cat', which refers to the animal's bad habit of raiding poultry runs. It is also known in England as the 'fitchet', from the old Dutch 'foule-marten', which refers to the animal's other bad habit, of squirting out a foul-smelling liquid when irritated, like its cousin the skunk.

The ferret is a smaller, tamer animal than the polecat, very pale in colour, with large patches of white around the head. The ferret fancier breeds for two different temperaments: 'docile' for chasing rabbits out of burrows, and 'aggressive', for killing rats. The programme of selection for these temperaments is quite rigorous with the young ferrets that display the unwanted temperament being put down or given away. There are a few wild ferrets in Britain, unscheduled liberations by owners who became bored with waiting for their pets to come out of burrows and gave up and went home. These, because of their tameness, do not do very well in the wild. The largest population of wild ferrets in the world is—in New Zealand.

The first ferrets arrived in 1867, imported by a private individual, a Mr Morton, and they were kept on his behalf by the Canterbury Acclimatisation Society in their Domain gardens. One more was imported in 1868, and the Society sold some, presumably the progeny, on behalf of Mr Morton. In July 1873 the curator, Mr Johnson, wrote to Mr Morton asking him to remove the ferrets as soon as possible. Presumably some Society members had complained about these bloodthirsty animals being kept in such close proximity to their treasured game birds. The Acclimatisation Societies were very much against the importation of ferrets, stoats and weasels, although in 1882 the Canterbury Society did agree to take charge of twenty ferrets for the New Zealand Government; by the end of the year the number of ferrets had increased to sixty, so that the hutch had to be enlarged, and in the following year twenty-three dog ferrets were sent to Otago. The societies could not do much more than complain about the ferret liberations, as they were the ones responsible, in many cases, for the introduction of the rabbit.

Despite the trials and tribulations of breeding and shipping ferrets, the Government managed to liberate nearly four thousand ferrets in 1884, on Crown lands in Otago and Marlborough. In 1885 two lots of stoats and weasels were shipped

page 170

Shipping fever

Throughout my research on the transport of animals in the nineteenth century, I have been struck again and again by the horrifying death rates that occurred on many of the animal-carrying ships of the time. The reason for this, in the case of birds, is quite simple—they moulted in the heat of the tropics and then caught cold and died as the ship moved south into cooler latitudes. Ships that approached New Zealand in summer had a higher success rate with shipments of birds, and, as Richard Bills found out on the Waimate, the birds had to be kept as cool as possible while crossing equatorial regions—iron-sided ships could be fatal.

With mammals the problem was more complex. It appears that the deaths may have been caused by a condition known now as 'shipping fever'. The bacteria which causes this condition is Pasteurella—a very common group found routinely in the nasal and digestive tracts of cattle, horses, pigs and most other mammals. If the animal becomes run down or fatigued or frightened, or is living in overcrowded conditions with poor ventilation or poor feeding, then the body's resistance systems, which are normally well able to cope with the Pasteurella bacteria, fall down on the job, and the animal sickens.

The disease that then appears is called pasteurellosis, and varies in its symptoms. It may appear as a swelling and bleeding of the liver and kidneys, or the head, neck and throat may swell, with the production of a lot of strangling fluid. The lymph glands may swell acutely, and there may be bleeding of the small intestine and colon. In other cases the disease looks like acute pneumonia, with the fluid discharge and bleeding that one associates with this disease. The animals get very sick and usually die very quickly, or may arrive miserable and ill, and die some time after landing. The disease is not normally transferred from one animal to another, although in special circumstances, such as long periods of upset and overcrowded conditions, this will happen.

The amazing thing is that pasteurellosis is not just found in cases of animals being carried long distances in the past under nervewracking conditions, but is a condition that is still very common today. Cattle that, in countries such as North America, are transported long distances for sales or fattening, die just as distressingly as their ancestors did in the wooden ships that sailed across the world. When one thinks of it, the same conditions apply—stress, strain and overcrowding. Because shipping fever is so common, attempts have been made to develop a serum or vaccine to combat it. These efforts have not been very successful, probably because the Pasteurella group of bacteria is such a large one. Dr Soltys, of Canada, a country which has a high incidence of pasteurellosis, says that when a group of eight horses was infected with Pasteurella by accident during a routine vaccination, injections of anti-serum, though immediate, failed to save even one of the horses.

Can man get pasteurellosis? He can, if he is bitten or scratched by an infected animal. When one reads accounts of how animals died because their keeper was ill in his bunk, one wonders if he may have had the disease that was killing them. How can shipping fever be prevented? Care and attention is the answer, with stock being well fed, kept quiet, tranquillised if necessary, and maintained in dry sheltered quarters away from disturbances. This list of conditions emphasises the skill and organisation that men such as Cook, Petre, Bills and Donne must have applied to be so successful in transporting animals halfway across the globe.

Perhaps the most interesting feature of the disease is that it is not a disease of New Zealand. In such a small country the animals are not carried the long distances that are associated with the condition. The days of carrying animals for long periods are over, although it is interesting to note that with the modern development of carrying stock from New Zealand to other countries by air, incidents of animals developing a type of stress-related 'pneumonia' are being recorded.

from London, and the survival rate was much better, as Mr Bayly had hoped, with 238 animals arriving out of 262 shipped. In 1886 more shipments, both private and by the Government, of stoats and weasels arrived, including one of 55 stoats and 167 weasels for Riddiford's station in the Wairarapa. In 1893 the Hawkes Bay Herald reported that 'weasels can evidently travel—for one was found dead the other day on Te Haroto run, Upper Mohaka, fully 150 miles from the nearest place where weasels had been turned out. Inspector Amyes, who found the animal,' the report continued, 'has been all over the Te Haroto district without finding any traces of rabbits. So it seems that the "eradicators" have reached the place in advance of the pest to be eradicated!'

All mustelids are very territorial, living in a solitary fashion and defending large tracts of ground from other mustelids. Because of this they spread very widely and thinly, which would account for this report. It would also account for opinions that the mustelids were failing to control the rabbit problem, as the satisfying sight of numbers of predators hounding down hordes of rabbits was never witnessed. Territorial behaviour dies down to allow mating when the female is in season, but during the rest of the year, once the 'kittens' have left the nest, the female and male page 172 mustelids defend their territory against each other. If food gets short the female will be driven away even if there are kittens dependent on her, so that mustelids practise a form of population control in times of hardship.

Mustelids are excellent swimmers, and will cross water to hunt, if necessary. The otter is the champion swimmer of the family but this fish-eater was, for obvious reasons, never suggested as an importation. The pine-marten (sometimes known as the 'sweet-marten' because it has no rank odour) was suggested as an importation; it is a cat-sized animal, known for its extreme agility. It is an expert tree-climber, so, while its fur is greatly prized, no-one really considered bringing it in, as the toll of bird life would have been enormous.

Weasels, stoats and, to a certain extent the ferret, thrived when they first arrived in the open country, their large increases in population aided by continuous liberations by the Department of Agriculture. They soon spread to all parts of the North and South Islands. The stoat was the most successful, being found now in all sorts of habitats, from fields and gardens to riverbeds and sand-dunes. The weasel is now much rarer, as when food became short it did not manage to compete with the larger stoat. There seem to be two sorts of ferret established in the country: the dark-brown polecat and the smaller paler ferret. Whether this is due to regression in the wild, or to the fact that both ferret types were brought out by the Government, is unclear. Because of the confusion, furriers took the solution of calling any ferret skin taken in New Zealand a 'fitch'.

The ferret, or polecat, or fitch, is much more restricted in its distribution than the stoat, being rare in North Auckland, the Bay of Plenty, Poverty Bay and Taranaki in


page 173 the North Island, and seldom seen in the western parts of the South Island. Ferrets are difficult to find because of their habit of hunting down in the burrows. They can become so lazy that they will take up residence underground in a warren for months on end, catching the occasional rabbit when their appetite inspires them and sleeping the rest of the time. McLean in Rabbits Galore! describes a time when he dug up a burrow and found a very sleepy fat ferret with six baby rabbits cuddled up around it, asleep.

The weasel is the smallest mustelid, with a head so tiny that reputedly it can run through a wedding ring—it can certainly run down mouseholes after its prey. It is also agile enough to scale trees to raid birds' nests, and it has a reputation for great ferocity. Stoats and weasels are similar in appearance, but the stoat is larger and has a longer tail. Adult male weasels reach about 28 centimetres from nose to tail tip, while the stoat is about ten centimetres longer. Female stoats and weasels are much smaller than the males, being only about two-thirds the length and half the weight of the males.

It is difficult to count stoat and weasel populations because of the animals' small size and agility. Their speed means that they often flash across the road before anyone can identify the sinuously scurrying animal. Whatever the numbers of ferrets, stoats and weasels, however, they are certainly much less numerous than they were early this century. When people became disgusted with the mustelids' apparent lack of effect on the rabbit populations, poisoning of rabbits with strychnine became commonplace, and the mustelids were poisoned by eating the tainted carcasses. Similarly, when the poison 1080 was used in later years, cats and mustelids died after


page 174 sampling rabbits that were sickening or had fallen dead. This did nothing to improve the bad reputation of the ferrets, stoats and weasels, as the few rabbits that escaped the poison could then breed unchecked, so that people blamed the reappearance of high numbers of rabbits on the poor performance of the mustelids, not realising that the predators had fallen prey to the chemical that was meant to eradicate the pest. Phosphorus was a much better poison as it killed the rabbits but did not render the carcass poisonous. However the mustelids could not win even then. As the rabbits died en masse the natural food supply of the mustelids ran out, so they had to turn to the alternative of any bird life that happened to be handy. The result of this was that, though mustelids and cats were declared natural enemies of the rabbit under the 1886 Rabbit Nuisance Act, and were protected in all areas, many acclimatisation societies quietly encouraged the trapping and shooting of the predators. After 1936, when the protection was removed, the societies immediately began paying bounties for weasel, stoat and ferret tails. While many canny trappers nipped off the tails and then let the animals go, with an eye to the production of future fur, this measure led to the destruction of many mustelids.

Between 1939 and 1948 a bounty was paid on nearly forty thousand tails. This was

page 171

Stoats and weasels

The weasel is a dogged and determined hunter, by its persistence taking prey that is often five or ten times its weight. There was a recent account published in a British paper of a weasel that was seen to attack a gull, clinging to its prey even when the gull flew up in the air and then dived into the water. Considering their small size, weasels take a surprisingly large number of rabbits; but they more often pursue and feed on rats and mice. Predation on ground-nesting birds becomes common only when the weasel's normal food supply runs low. In Britain the weasel has been recognised as a pest by bird societies only since most of the British rabbit population died out from myxomatosis.

It is commonly believed that stoats and weasels drink the blood of the victim, leaving the flesh for other animals such as cats and ferrets. This Dracula-like reputation is completely undeserved; when the predator sinks its needle-like teeth into the victim's neck the blood runs down the gripping snout, which makes the assassin look as if it is sucking the blood, but after the death—which is very quickly delivered—the stoat or weasel eats all of the animal except the front part of the skull, the feet and the tail. The intestinal contents probably furnish the mustelid with necessary nutrients such as vitamins and fibre.

Stoats and weasels usually prefer to live alone, but this solitary behaviour is abandoned during the breeding season. Female stoats have the amazing ability to put off pregnancy until the time is favourable; after mating the fertilised eggs float around in the womb until the following spring, when they will embed themselves and start to develop into embryos. The 'kittens' are born in a nest which will be a burrow in a bank or a hollow tree. They are fed on milk for the first few weeks, and then the mother brings them live food to kill and eat, stunning baby rabbits with a single blow of her powerful jaws, and dragging the unconscious bodies into the nest. Young stoats and weasels have to be taught to hunt, so at certain times of the year they can be seen hunting in family parties. Once the kittens can cope on their own the family breaks up as the members go off in different directions to find their own territories.

Stoats can be distinguished from weasels by more than the difference in size, as the stoat's tail is much longer, and has a black tip. Both stoats and weasels are capable of turning white in a very cold winter, although this is not recorded very often even in Southland. When a stoat turns white the black tip to the tail remains, and the animal gets a magnificent new name: ermine. It is this fur that adorns the edges of royal robes.

There is a whole folklore in Europe about stoats: stoats are meant to be able to charm birds into their reach by hypnotic dancing—a sort of rolling around in sinuous gymnastics. The birds flock to watch, and some of them become so mesmerised by the sight that they fall off the perch and into the waiting jaws. There have been so many documented observations of this that it must be founded on fact. It is observable that birds are attracted to any sort of rhythmic behaviour, and stoats, being naturally playful, probably find this out by accident at an age young enough to take advantage of the lesson. Less well documented is the superstition that stoats, like elephants, mourn their dead and take the bodies to a secret resting place.

A stoat or a weasel hunting a rabbit is a riveting sight. The predator never seems to hurry, but travels doggedly along with its nose close to the ground, while the rabbit scurries madly, often in panic-stricken circles. The mustelid has a poor sense of sight, and when the rabbit runs in circles it often 'laps' the predator, running past it close enough for a snatch, but the mustelid ignores it, keeping determinedly on with its nose to the scent trail. The rabbit squeals loudly towards the end of the chase, often crouching still and rigid, with its eyes glazed with terror. However this does nothing to deter its terrible pursuer. The mustelid strikes in the back of the head, its sharp teeth penetrating the skull and killing the rabbit instantly.

not the whole story, either, as the skin, which had to include the tail, was valuable, fetching up to two pounds sterling for a good fitch skin. In 1946, a peak year, over forty thousand fitch skins and over sixteen thousand stoat skins were sold on the New Zealand market.

Whether or not mustelids and cats helped control the rabbit population will always be somewhat of a mystery. They were certainly found where rabbit populations were high, but they were also seen in areas where there were no rabbits at all. Studies of stomach contents have shown that mustelids eat birds, domestic fowls and their eggs, frogs, rats, young rabbits and mice. With the dearth of rabbits to hunt, stoats and weasels had to do the best they could with the supply of vermin. Normally stoats prefer not to have these animals as the staple of their diet, but once the rabbit supply dried up, the stoat was forced to compete with the weasel for rats and mice, and as the stoat is a bigger stronger animal, it succeeded at the expense of the weasel. This left the weasel with no choice but to eke out its existence by hunting out birds and their nests. Naturally this led to greater predation of native and introduced game birds and weasels have a very bad reputation because of this. There is however no programme of control of weasels, although they are quite often caught and exterminated because page 176 of their habit of tracking a scent trail and ending up in rabbit and opossum traps. Their numbers have certainly diminished greatly.

Many consider today that the cat was a better predator of rabbits than the mustelids, as the cat was sufficiently domesticated to come to the homestead for food when rabbits were short, and therefore survived until rabbits increased again. And yet cats more fully deserve the reputation of preying on birdlife. The lighthouse keeper's cat exterminated the Stephens Island bush wren in 1894. Cats have wiped out several species of land birds on Herekopare Island near Stephens Island. Since wild cats were eliminated on Cuvier Island in the Hauraki Gulf, saddlebacks have been able to re-establish a population there.

A team led by Dr Gibb investigated predation on rabbits by cats and ferrets in the Wairarapa from 1957 onwards. In an enclosure of 8.5 hectares at Kourarau station, predation by three or four cats and five or six ferrets, all with free access, reduced a population of over a thousand rabbits to only thirteen in three-and-a-half years. The cats hunted above ground and the ferrets in the burrows, so that with this division of territory the predators prevented any young rabbits surviving longer than a week or so. In the spring of 1963 the predators were excluded, and less than two weeks later young rabbits were romping around the warrens; by the spring of 1965 rabbit numbers were higher than when the observations were first commenced.

That then is the story of the ferrets, stoats and weasels, brought out here against the wishes of many people, travelling under what must have been nightmare conditions, and then regarded with animosity from the day they arrived. Donne wrote, 'It was a case of trying to cure a curse with a curse and naught but a curse remains.' Ironically enough, the acclimatisation societies, which were very much against the introduction of ferrets, stoats and weasels, were often blamed for the importation of these animals. A settler wrote in the 1930s, 'Many of the native birds have disappeared . . . The stoats and weasels, no doubt, are responsible for their destruction . . . The Acclimatisation Societies are responsible for a number of objectionable importations. I think it would have been better if they had gone on the principle of letting well alone in the animal and bird life.' And yet the mustelids did not turn naturally to killing native and introduced birds in great numbers; the problem was more one of bad management. If the natural food supply of a control disappears, then it does not commit convenient suicide—it finds itself an alternative food source. The mustelids of Britain did not turn to preying on bird life until most of the rabbit population was dead of myxomatosis.

In 1883 Bayly said in his report that 'it has been suggested that disease should be introduced; but hitherto the risk to be run to stock and human beings in pursuing this course has been considered too great to attempt it.' During the summer of 1950-51 the use of myxomatosis to control rabbits in Australia and Europe met with great success. Accordingly, trials were held in New Zealand, but even when healthy rabbits were put in cages with infected rabbits, they failed to catch the disease. The problem, apparently, was that the myxomatosis virus needs an insect carrier, or 'vector', to pass it from one rabbit to another. In Australia the stickfast flea was the main transmitter, but, for obvious reasons, no-one wanted to introduce this insect to New Zealand. Mosquitoes are also vectors for myxomatosis, but the New Zealand varieties lacked talent in this respect; even when the hutches of infected rabbits were placed on the page 177 edges of mosquito-ridden swamps, the rabbits in the wild remained as healthy as ever.

So the idea was abandoned, with no great regret. New Zealand at that time already had a strong programme of rabbit control which was working well; no-one really wanted to see disease-ridden rabbits limping blindly around the landscape. Myxomatosis is a particularly horrible affliction: about a week after infection the rabbit's eyes begin to weep with a watery discharge, and then the eyelids swell up and become broken and crusted; this condition spreads to the anus, nose and genitals, and then jelly-like lesions break out all over the body. The rabbit dies thirteen days after infection, after a week of blind agony.

Viruses similar to myxomatosis can be used to control certain insect pests: a sprayable virus has been developed to combat the cabbage-white butterfly and the future of this type of control looks quite promising. A fungus native to New Zealand is also a type of control by disease. A caterpillar such as that of the porina moth ingests some spores of the fungus, Cordyceps, and the fungus grows through the body of the caterpillar, turning it hard and woody after killing it, so a sort of 'vegetable caterpillar' is produced. The Maoris prized these, as they could be ground up into a powder which was used for dyeing tattoos.

Biological control by disease whether indigenous or introduced can be very unattractive, but it often has the advantage of being one hundred percent effective. When predators or parasites are brought in as controls, they can be less satisfactory, as in nature biological suicide is avoided—the predator or parasite will not wipe out its prey entirely. This is a distinct disadvantage for the farmer or scientist who brings in a predator or parasite as the control of a pest, but in a country which depends on farm and forestry for the major part of its overseas exports, there is always incentive to introduce a control and take the disadvantages with it, in the hope of getting even a partial reduction of pest numbers. Several insect controls have been introduced over the years, the most successful being those which prey on woolly aphis, the cabbage white butterfly and the woodwasp.

page 175

Biological control

Biological control is the use of parasites and predators to control pests. There are several important features of its employment. A hundred percent control of the pest must not be expected, as no efficient predator or parasite would wipe out its entire food supply.

Intensive research into a biological control must be carried out prior to introduction, to make sure that the control will not become a pest itself, by attacking some plant or animal that is itself desirable.

The background of the control must be known intimately. Is it carrying some disease? Does it have any parasites of its own that should be kept out of the country? Can it adapt to the new conditions?

In the enthusiasm of the nineteenth century these basic precautions were very often forgotten.

Apple woolly aphis is easily recognised because of its fluffy covering. It has been known in New Zealand since the 1840s, and it is found throughout the country as a pest in apple orchards. One natural enemy was already present—the native ladybird Coccinella tasmanii—but significant control of the pest was not achieved until a little parasitic wasp, Aphelinus mali, was introduced from America early in 1921 by Dr Tillyard, Chief of the Biological Department of the Cawthron Institute, Nelson. In introducing these wasps Dr Tillyard unwittingly introduced some other insect species along with them. None of these were fortunate imports, as two or three were chalcids, which parasitise the parasite, and the other was a moth, Nepticula, whose caterpillar is a leaf miner on apple trees.

Pteromalus puparum is another parasitic wasp; it controls the cabbage white caterpillar. The wasp 'stings' the caterpillar with its ovipositor as the caterpillar chews its way unfeelingly through a cabbage leaf, and lays its eggs inside the

page 178

Sirex—the timber bandit

Very elegant members of the insect family are the slender, agile ichneumon wasps, many of which are parasites and can be used in programmes of biological control. One of these however, Sirex noctilio, accidentally introduced into New Zealand from Australia or Europe in a cargo of timber before 1900, was by no means a welcome immigrant: it has the unfortunate habit of laying its eggs in radiata trees.

The female wasp has the remarkable adaptation of being able to bore into hard timber by using her long hair-like ovipositor. When boring she stands on her head, bringing the ovipositor forward between her hind legs, and thrusting the boring end of it rapidly into the tree. As with a dentist's drill, the drill of the Sirex ovipositor must be lubricated, and for this she produces a mucus, which as well as helping the drilling process, has a toxic effect on the tree.

The female is attracted to weak or damaged trees because of the scent they produce. Once she has found such a tree, she drills with her ovipositor to test its suitability. If it seems satisfactory she makes a number of holes, laying eggs in all but the last one. In pockets situated on each side of the end of her abdomen she carries a special fungus, and in the last hole she deposits some of the spores of this. The mucus she has used as a lubricant causes wilting and yellowing of the needles of the tree, so the Sirex infestation can be seen before long, both by these symptoms and by the series of holes in the trunk, which could be dripping with resin. The growing fungus dries out the wood and interferes with the conduction of water in the trunk: the combined effects of fungus and mucus can kill the tree before long, if conditions are right.

The eggs of the Sirex hatch in nine days or so, though they can remain dormant, which probably explains how they managed to live in timber long enough to invade New Zealand. Once hatched, the larvae tunnel through the wood, apparently living on the fungus and gaining all nourishment from this. When the larva is full-sized it will pupate. Before females emerge, some of the fungus will pass up the ovipositor and into the pockets of the abdomen that are prepared ready for the fungus spores.

Thus the adults, varying in size, but often reaching 36 mm in length, emerge from the trunk of the tree. They usually mate, so that the female has a store of sperms; but it is the way she lays her eggs, in the odd manner of all the wasp and bee family, that determines the sex of the offspring. If the egg is unfertilised, it develops into males only; if the egg is fertilised, the progeny will be either male or female. Thus a female Sirex, even if unmated, can still lay eggs in timber and these will grow into grubs.

Mated or unmated, the female will place fungus spores into the wood with her eggs. This is an amazing feat of biological cooperation, but one with undesirable consequences in the timber industry—although trees, to be badly affected by Sirex infestation, have to be unthrifty, crowded or badly damaged in some way—so a number of controls have been introduced to combat the insect. Biological control, with good forest management, is the only answer, as, obviously, spraying with insecticides has no effect on the grubs boring happily away deep inside the trunk of the tree.

Female Sirex drilling into living radiata pine to insert eggs, fungus and toxic mucus. Note drill between two back legs. Length of insect 30 mm.

Female Sirex drilling into living radiata pine to insert eggs, fungus and toxic mucus. Note drill between two back legs. Length of insect 30 mm.

caterpillar. The grubs of the wasp hatch out while, rather grotesquely, the white butterfly larva chews on, often only a liquid hulk inside its quivering skin. Amazingly, the caterpillar often grows to full size, with its cargo of parasites inside, but it does not live to pupate, as the wasp grubs bore portholes in the caterpillar's skin and emerge to make little yellow cocoons along its sides while the caterpillar finally expires. In due course the wasps hatch out, to mate and then hunt for more cabbage white caterpillars to be hosts for their progeny.

The woodwasp, Sirex noctilio, is a pest of exotic pines and has caused severe damage in unthrifty stands of Pinus radiata. Though a very fragile-looking creature, the Sirex female has a long ovipositor which is strong enough to be inserted deep into the woody trunk of a pine tree. When it has bored its way into the timber the eggs are laid, along with some spores of a fungus. The fungus grows and spreads rapidly inside the tree, killing and drying the wood. The Sirex grubs then feed on the fungus. This is page 180 an amazing biological phenomenon, but one that has the potential to greatly reduce New Zealand's export receipts. Although a native wasp, Guiglia schauinslandi, parasitises Sirex wasps, more biological controls were needed. Rhyssa, introduced in 1929, has only limited effect, so Ibalia was introduced from England in 1951; the combination of these two has been more successful. Ibalia uses the hole drilled by the

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Insect assistant number one—Rhyssa

After the damage that the accidentally-introduced Sirex wasp caused in pine forests became obvious, the New Zealand Government consulted with the Imperial Institute of Entomology in Britain, and then received, in 1929, a shipment of 1 300 larvae of the European ichneumon wasp Rhyssa persuasoria. These had been collected from infested tree-trunks in English woods. Further importations took place, and the wasp was also bred in the Cawthron Institute in Nelson.

Rhyssa is an attractive little insect, with the female easily distinguished by the very long ovipositor that trails behind her. The body is black, with white markings. The female Rhyssa is attracted to trees that have the fungus carried by Sirex growing inside the trunk, enticed by the smell of fungus. She drills around the trunk in a random pattern until, at last, she strikes a Sirex larva. She then stings the grub, and paralyses it so that it is motionless but living prey for her young to feed on. An egg passes down her ovipositor and lies on the skin of the Sirex grub. The egg hatches in a day or so, and the Rhyssa grub feeds luxuriously on its captive meat, in leisurely fashion, and then lies in the Sirex tunnel and eventually pupates. The adult, when it hatches, bites its way out of the wood and flies away, continuing its honeyed existence by feeding on nectar and the sweet dew excreted by aphids and scale insects.

Rhyssa drilling into a radiata pine tree to sting, paralyse and lay an egg on a Sirex larva. The ovipositor is about 40 mm long, while the body is 35 mm long.

Rhyssa drilling into a radiata pine tree to sting, paralyse and lay an egg on a Sirex larva. The ovipositor is about 40 mm long, while the body is 35 mm long.

Sirex female to lay an egg inside the Sirex egg. Rhyssa is even more amazing to watch in action. By some finely tuned sense the females are able to locate the Sirex grubs deep inside the tree, and then with precise care and infinite skill the long hair-like ovipositor is inserted, unerringly searches out the grub, and injects the egg onto it.

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Insect assistant number two—Ibalia

Ibalia was deliberately brought from Europe in 1950 and 1951, and was first liberated in 1954, after intensive study, in approved scientific fashion. It is now well-established almost everywhere Sirex occurs in New Zealand.

Ibalia is quite a bit smaller than Sirex or Rhyssa, its 16 mm being about half the length. The ovipositor does not trail behind, being retracted inside the body when not in use. Both sexes are distinctive in that they are flattened sideways like fleas. The female Ibalia detects by smell a recent drill-hole made by a female Sirex when egg-laying. The Ibalia uses the same hole, then pierces the Sirex egg, laying her egg inside the Sirex egg so that when the Sirex grub hatches it already has a parasite growing inside it. The Ibalia can lay her egg inside an already-hatched Sirex grub, but this only happens if the Sirex grub has not moved away from its hatching site; the Ibalia female has to use the Sirex female's drill-hole, as she has no timber-drilling apparatus herself.

The Ibalia larva grows inside the Sirex grub for several months, savouring the meal, and then bites its way out to eat the moribund remnants. It then pupates, and the adult after hatching chews its way out of the wood. Like Rhyssa, the Ibalia adults live on honeydew from aphids and scale insects. Ibalia and Rhyssa, with some other biological controls, keep the numbers of Sirex wasps down very satisfactorily, killing perhaps seventy percent of the pests. With good forest management, the infestation of the accidental immigrant Sirex can be said to be well under control.

Ibalia female egg-laying down a Sirex drill-hole.

Ibalia female egg-laying down a Sirex drill-hole.

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A control that nearly became a pest was a beetle, Coraebus rubri, which attacks blackberry. While it was being studied it was discovered that it also attacks loganberries and boysenberries, fortunately in time for all the beetles to be destroyed before they could endanger these plants which—along with the modern cultivated blackberry—show great promise as horticultural exports. More successful was Apion ulicis, a weevil introduced to control gorse. This weevil bores into gorse seeds, and eats them so that they cannot germinate—a valuable aid, considering that gorse seeds can remain dormant and then germinate, even after burning-off, more than forty years after dropping.

In 1930 the moth Tyria was introduced as a control of ragwort. This looked promising at first, but then the Tyria caterpillars were attacked by a native parasite of the indigenous magpie moth.

Some biological controls were introduced accidentally. One important ladybird, the Australian ladybird, was first recorded by surprised naturalists in Wellington in 1894. By 1899 it was having such good effect, virtually eliminating cottony cushion scale in citrus trees, that the Agricultural Department introduced some more. Its cousin the common ladybird was recorded as swarming in great numbers near Tinakori, Wellington, in 1899. In 1896 a Captain Broun had claimed that he was importing common ladybirds throughout the Waikato district, so the Tinakori ladybirds may have been a migration from his deliberate introductions. By 1919 ladybirds were common in the Taranaki, and soon after that they were found in some numbers throughout New Zealand. The common ladybird eats the aphids that attack turnips, cabbage, garden plants and shrubs so it was a very welcome introduction. American ladybirds were introduced by the Agricultural Department and private individuals in 1899, but these were never as successful as the various Australian ladybirds. The blue ladybird is another Australian ladybird, and since its arrival it has done a great deal to control the scale insects that attack citrus and gum trees. The Australian red-headed ladybird was introduced into North Auckland to control mealy bugs and scale insects; it is now common there, although it is too cold for it to breed south of Auckland. Both these Australian ladybirds were introduced by the Department of Agriculture around 1899.

The praying mantis was an accidental importation, arriving in the early days of European settlement, in loads of hay. It was first reported in the 1850s, and is now common throughout the country, making meals of any insect unwise enough to stray within range of the striking front legs. Various ichneumon flies have become acclimatised, both accidentally and on purpose, and these do good work in controlling porina moth caterpillars, flax grubs, army worms, diamond-back moths, and greenfly. One of these ichneumon moths was imported and bred by Mr T.W. Kirk in 1895, who reported, '. . . having succeeded in rearing from the parasitised "puparia" of Hessian flies, received from England, a large number of the icheumon fly, known as Semiotellus nigripes, which were liberated in the various districts where the crops had suffered from the attacks of the Hessian fly.' This control was most welcome, as the Hessian fly is a dreaded pest of oat, wheat and barley crops. The Government arranged for some thousands of infected puparia of the Hessian fly to be sent from England, and since then the incidence of the Hessian fly has decreased to the stage that it is now insignificant as a pest.

A much less popular introduced biological control was the owl. When, in the 1880s, the small birds introduced from England turned out to be such an embarrassment in the richness of their fertility, many people suggested bringing out their natural enemies the owls. Others, fearing for native birdlife and introduced gamebirds, were as determinedly against such idea. As early as 1873 Sir Walter Buller sent out from England a pair of wood-owls, but, as he said sadly, 'the unfortunate immigrants fell victims to popular prejudice.' In a word, they were shot.

A similar fate befell the barn-owl, which was introduced by the Otago Acclimatisation Society in 1899. The Society wrote plaintively, * ... as they live almost entirely on rats and mice, we feel sure the public will protect them.' The public, understanding immediately the faulty logic—that a bird introduced to control small bird nuisances was not likely to favour a diets of rats and mice-dispatched the unlucky owls within a year.

A more determined introduction of another owl, the small brown owl, was made by the Otago Society in 1906, when it imported 28 birds from Germany. In 1907 39 more were introduced, and in 1908 a third shipment of 80 was received. These were distributed all around the area, with many being liberated at Alexandra. In 1909 the Society was greatly encouraged by the favourable reports that were coming in from local orchardists, so they imported another 72 birds in 1910. The orchardists and farmers were so much in favour of the owls by then that the Society was able to sell 58 of the birds and recoup some of the expenses.

The black swan is one of the successes of acclimatisation. Some time previous to 1864 the Nelson Society imported seven birds; and then in 1864 the Canterbury Society received four birds from Sir George Grey, and liberated them on the River Avon. Further introductions followed, and the birds quickly established themselves, spreading into most parts of the South Island.

The black swan is one of the successes of acclimatisation. Some time previous to 1864 the Nelson Society imported seven birds; and then in 1864 the Canterbury Society received four birds from Sir George Grey, and liberated them on the River Avon. Further introductions followed, and the birds quickly established themselves, spreading into most parts of the South Island.

By 1918 the small brown owl had spread all over Otago and some had been taken to the North Island. A naturalist, Mr A. Philpott, wrote in that year, 'There can be no doubt that such introduced birds as the sparrow and others which roost about hedges, plantations, and buildings will pay a heavy toll; indeed, I have reason to think that the thrush, the sparrrow, and the starling are already diminishing in numbers near Invercargill. Where a pair of owls have established themselves,' he went on with relish, 'the evensong of the thrushes and blackbirds gives place to an incessant chorus of terrified alarm-notes.'

The acclimatisation of the small brown owl has been successful in the South Island, in that the bird is now abundant from mid-Canterbury to Foveaux Strait in the drier eastern areas. It has been sighted in the Wellington area, but is not at all common there. Reports of its value to agriculture are now not as warm as they were in the beginning; with destruction of small birds by the owls the insect pests have returned in force, and Otago farmers say that the grassgrub is much more a problem than it used to be, because of the lack of predators. The bird societies dislike the owl intensely, as it kills many native species including bellbirds, fantails, greywarblers, shining cuckoos, and even the young of the grey duck. There is also evidence that where the little owl has thrived the native morepork has suffered because of competition for food. All in all, in the eyes of the conservationists, the importation of the small brown owl ranks as one of the most unpopular.

If the mustelids and the little owls are the villains, and the ladybirds and ichneumon wasps the heroes of the drama of introduced biological controls in New Zealand, then the black swans would have to be the comedians. And yet the introduction of black swans looked quite straightforward. It wasn't any elusive and controversial animal pest they were to track down and exterminate, but merely a massively overgrown weed, waiting in the River Avon for them to gobble up.

The plant introduction which flourished in that exuberant fashion was the common watercress, introduced into the Avon River in the early 1850s. It responded to the marvellous new environment by growing to gigantic proportions, sprouting triffid-like into branches five meters or more in length, with stems like enormous ropes. In 1864 the Canterbury Acclimatisation Society received two pairs of black swans from Sir George Grey and liberated them into the river; it had been suggested that these birds might clear away some of the rampant growth. Observing this, the Christchurch City Council discussed the matter at a meeting in August of that year and resolved to set up a 'Committee of Swans'. This body was formed, and visited the Deans property at Riccarton to look at a couple of swans there. They were so impressed with the job of clearing the birds had been doing that they recommended that the Council import some black swans itself. After reading the report the Council sent to Sydney for thirteen pairs, and these were released on the Avon.

Up until this development the Acclimatisation Society had seriously thought of importing some water buffalo, remarking on the 'docility, great strength and superior quality of flesh' of the animal, but this idea was shelved when the swans arrived. What the buffalo would have done is open to conjecture; what the swans did was immediately quit the river and fly off to other parts. Two were caught down at the Estuary and were brought back, only to fly off again. The city surveyor did his best, making little houses for the swans, and putting food (surely defeating the object of the page 185 exercise) in troughs. Despite all this by 1867 the swans had reached Marlborough, the West Coast and Otago, and were congregating in large flocks on Lake Ellesmere. Only one or two remained on the Avon River, and these didn't get round to multiplying; on Lake Ellesmere the increase was so rapid that by 1871 flocks of over 300 were being reported, and in 1875 the black swans there were declared to be game, and could be shot during the waterfowl season.

Today Lake Ellesmere has a black swan population in excess of seventy thousand birds. The Avon River still has some watercress growing in it, although this weed was greatly reduced when willows were planted on the banks, as the roots of the willow trees compete with the cress for nutrients in the river bed.

A surprisingly unpopular importation was the hedgehog. There seem to have been some odd superstitions linked with this animal in Britain. It was said that hedgehogs killed chickens, coming back every night until the coops were completely denuded of occupants. It could be easily seen when a hedgehog was the offender, because hedgehogs ate the stomach first, while a cat will eat the breast first, and a ferret or stoat will go for the head and neck. Hedgehogs dug up potatoes, it was claimed, and spoiled one's vegetables. Another belief was that hedgehogs jump up and hang onto the teat of a cow in milk, swinging happily while sucking the udder dry—something of a bovine nightmare.

In 1870, according to Thomson, the Canterbury Acclimatisation Society received a pair of hedgehogs from Mr D. Robb, the purser of the Hydaspes. The Society received another in 1871: a Mr Nottidge sent the Society a batch of rooks and jackdaws, and included with them went twenty hedgehogs. As usual at that time, the death rate in the animal cargo was dreadful, and only two jackdaws and one hedgehog arrived alive. In 1885 a shipment of one hundred hedgehogs was consigned to the Otago Society, but at least one of the animals must have been a carrier of some hedgehog disease, or else an unrecorded calamity took place on board, as only three survived the journey. They were liberated in a Dunedin garden but were sick and sluggish. The female died a month or two later, and the two males disappeared.

By this time, some sensible counsel was being heard on the subject of liberating hedgehogs as a control of slugs and snails. In 1879 at a meeting of the Hawkes Bay Acclimatisation Society, when the destruction of hawks was being discussed, a Mr Tiffen, tired of hearing how valuable pheasants were because of the habit of eating insects, suggested that the hawks be spared and hedgehogs imported to keep down the insects instead. The meeting did not carry his motion, but in the meantime many private liberations of hedgehogs were taking place. Guthrie-Smith, in Tutira, writes that there was a great migration of hedgehogs from the south to the north, very much aided by constant private introductions of the animal.

The hedgehog spread very rapidly, increasing in numbers so that it is now extremely common throughout the North and South Islands, avoiding only the very high country and large forests. It is the only insectivorous mammal in New Zealand, and has become abundant from lack of competition for this niche. It is a very successful biological control, eating slugs, snails, millipedes, caterpillars and sometimes frogs. It took a long time, however, for hedgehogs to entirely lose their bad reputation; some of the acclimatisation societies were convinced that hedgehogs eat eggs of game birds; they paid bounties for hedgehog snouts.



The abundance of hedgehogs can be judged from the fact that despite much lighter traffic, fifty times as many hedgehogs are killed on New Zealand roads as on similar road distances in Britain: Guthrie-Smith marked their migration 'by mangled remains of pioneers on the car-infested Napier-Wairoa road.' They are now recognised as a friend of the New Zealand gardener—and there has not been a single report of a hedgehog swinging from the udder of a cow.

And so, in the drama of biological control in New Zealand, the hedgehog snuffles furtively in the darkness, crushing his prey in the depths of the night; prickly customer he may be, but certainly not the villain of the extermination squad.