Tuatara: Volume 9, Issue 1, September 1961
Notes on the German Wasp Vespula germanica
Notes on the German Wasp Vespula germanica
The swift flying, brightly marked yellow and black wasp Vespula germanica is becoming common over most of the North Island, and there is a scattered occurrence in the Nelson Province. The wasps are notable for their singleness of purpose and persistence in their work, and especially this is the case when in the late summer and autumn they are attracted into houses in search of sweet foods.
An effective trap can be made for these searching wasps by placing a short funnel in the neck of a large bottle. A suitable brew of jam or rotten fruit put in the bottle will attract the wasps to the trap.
Although the wasps are hard to distract from the job in hand they are quite tenacious if aroused, and will devote themselves completely to removing the cause of their annoyance. Movement around the entrance to a nest burrow quickly brings a circling defence of watchful wasps, whose numbers grow as the danger approaches. It may often be the case, however, that the defenders will not actually land on a person until the nest burrow is interfered with. The sting, which is quite painful, can be inflicted repeatedly by workers and queens, but not by drones, and the effect of the sting varies with the person, as it does with a honey-bee sting. Occasionally worker wasps have been seen caught in spider webs, from which they have nearly always been strong enough to escape. Several times wasps have been seen held in a web on to which the resident spider was hurrying to inspect the catch. Each time however, the spider, after approaching a short distance, turned and scuttled away, apparently not eager to tackle such formidable prey.
Once a blowfly with one wing, and a worker were seen tangled in conflict for about two minutes on a pavement. The fly managed to break away, and the wasp, left several inches distant, busily cleaned its head and antennae. After a few seconds the wasp turned and grasped the fly again. This time the pair spun around and around on the ground with the wasp on top. Eventually the fly escaped again and spun about three feet away. After a pause, the wasp moved quickly to a small brown piece of curled leaf about one foot away, and attacked that for a period. Upon finding that it had lost track of the fly, all the wasp's interest apparently vanished, and it flew to a nearby Clematis vine. Presumably the fly eventually died.page 25
The spread of Vespula germanica in the North Island has been both rapid and unhindered to the present time, while the distribution in the South Island will undoubtedly widen. The origin of the spread is Hamilton in the Waikato, where in 1945 a number of nests were discovered. It is thought that some queens in hibernation arrived from Europe late in 1944 with aeroplane parts. Prior to this time, in 1922. some German wasps were identified in the Wairarapa, but apparently did not become established. Since 1945 the wasps have increased their range by natural means, but large distances have been covered mainly by rail and road transport carrying hibernating queens. Now, in 1961, Vespula germanica is numerous, and in having some affect on apiaries and orchards will grow in importance as its distribution widens. In an address to the 1960 Ecological Society conference, Dr. R. A. Cumber reported that in the north of the North Island Vespula germanica has depleted numbers of another previously common introduced wasp, Polistes humilis, possibly by competition for Lepidoptera larvae and flies on which both species feed. With regard to possible control of the German wasp, Thomas (1960) mentions an ichneumon wasp Sphecophaga burra as the most likely parasite.
Vespula germanica is easily identified at rest or in flight, since the body markings of bright yellow and black are so striking. The yellow colour of the body markings can be contrasted with the old-gold colour found in honey-bees. The queen, worker and drone are shown in Figures 1, 2 and 3 respectively, drawn to scale so that the body sizes can be compared. To help identify any wasps caught, especially specimens such as queen-sized drones, the following features can be used:
The antennae of drones have 13 long segments so that they are about one and a half times the length of the antennae of workers and queens, which are composed of 12 short segments. The abdomen of the queen is about the same length as that of a drone, but much broader, while the thorax and head are considerably larger. The worker abdomen is shorter than the drone abdomen, but the thorax and head are about the same size.
Apart from any wasps that may be discovered in a nest, wasps are most likely to be seen in the following ways:
Hibernating queens can be found in winter in many sheltered positions, such as under wood in a stack, or old sacks, in disused buildings or beneath loose bark. These queens are easily collected.
In spring the new queens emerge from their hibernacula and are often seen cruising backwards and forwards along banks searching for nest sites. They will frequently settle near, or hover over, cracks and burrows in the ground for a short time before moving on.page 26
Workers will be seen on occasions, mainly in summer and autumn, engaged in collecting food (mainly insects) or wood fibre from lamp-posts, or coming and going from a nest burrow entrance.
Also in mid-summer and autumn drones and workers will come into the house in search of jams, fruit, meat and cakes, in fact a wide range of scented foods and liquids, and will be found in fruit either fallen or on the tree. The wasps will enter the fruit through a skin blemish, often caused by another insect, and will hollow it out completely leaving only the skin. In the middle of Wellington city in May, drones have been attracted by meat pies. In February in the Kaweka Range. Hawkes Bay, a worker was seen to drop on to a leg of meat, snatch a blowfly, and fly swiftly away. Blowflies are near in size to a worker, but the wasps will tackle insects much bigger than themselves.
In middle and late autumn drones can sometimes be seen weaving around the tops of bushes and trees prior to mating. In Wellington in May, drones have been seen flying in this apparently aimless manner round a Cupressus macrocarpa hedge for several hours on end.
Early in spring a mated queen comes out of hibernation and searches for a nest site, in a bank, hollow tree, or some other sheltered place. Sites which are exposed or which later prove unsuitable are often abandoned. The nest built by the queen comprises only several worker cells, and is a few centimetres in diameter.
The queen begins laying almost immediately, and larvae hatch after about three days. The cells are enlarged by the queen to keep pace with the growing larvae. The larvae moult three times and then pupate, the cocoon closing the end of the cell. The time taken for full development of a worker from a larva is not known accurately, but is between four and six weeks.
The fully formed workers chew open that part of their cocoon which closes the lower end of their cells, and emerge, ready to work after a period. Newly hatched wasps are not as bright in colour as older wasps, and have a superficial grey appearance owing to the retention of a thin covering formed round the pupa in the cocoon. Later this covering comes away revealing the distinctive yellow and black body markings of the adult insect. When the first workers have emerged, the queen devotes herself to egg-laying, while the workers enlarge the nest by adding new combs to the original comb built by the queen.
Fig. 1 : Queen, lateral view. Fig. 2 : Worker, dorsal view. Fig. 3 : Male, dorsal view. Fig. 4: Nest in bank. Part of the nest wall has been removed to show the internal structure. (One quarter natural size.) Drawn by Julia M. Mason
Thomas (1960) offers the explanation that drones come from eggs laid only by workers, even when there is a queen present. Also in some nests large drones are produced in queen cells in late autumn. These drones have not been seen to mate, and Thomas suggests that they are raised from unfertilised eggs laid by the queen after exhaustion of sperm in the spermathecae.
When new queens have matured in late autumn, mating commences. The drones leave the nest and congregate round nearby bushes and trees until the queens emerge, following which mating occurs.
After mating, and a brief return to the nest, the queens seek a place in which to hibernate for the winter, while the drones remain in the nest. As winter approaches workers and drones search widely for food, eventually turning on each other as well as remaining larvae and pupae until the nest is left empty.
In places where frosts are uncommon a nest with its functional queen may remain active instead of being deserted by the colony. Sections of the nest may be closed off by papery partitions, while the combs in use may carry worker, drone, or queen broods, the last being the most common. The following spring the colony picks up again to repeat the previous year's activities, and may possibly remain active for a further season if conditions are suitable. Hibernating queens emerge in spring and search for nest sites to commence new colonies.
A mated queen emerges from hibernation in spring.
The queen finds a nest site and establishes a small nest.
The first workers produced take over nest maintenance while the queen settles down to lay eggs.
In late summer and autumn drones and new queens are produced.
Drones and new queens mate, following which the queens hibernate.
Activity in the old nest decreases as winter approaches, and eventually ceases.
Occasionally nests may remain active over winter if conditions are suitable, and may be active through a second summer.
The nest is commonly situated in an earthy bank (see Fig. 4) and is usually a foot or two below the surface, though a nest may grow to be close to the surface, In one nest investigated the nest wall was only a quarter of an inch from the surface of the bank which was not very stable, and workers were seen dabbing bits of soil with their jaws on to the outer side of the thin portion of the bank. The ‘dabbed’ portion covered some four square inches, and was quite noticeable. Presumably the original burrow was short, and the nest quickly grew out towards the surface.
Nests may be above ground, however, in suitable sites in trees or buildings but this is less often the case. A nest may range in size from a few cells occupying one or two cubic inches, to a structure several feet in diameter.
As shown in the figure, the nest partly hangs from grass rootlets immeshed in the wall, and partly rests on the stone and pebble foundation. Nests near the ground surface may have so many rootlets caught into the walls that removal of the nest intact is extremely difficult. Usually one entrance leads to the nest and the burrow may curve vertically or horizontally before the chamber is reached. The burrow may not open directly opposite the entrance to the nest itself.
The shape of the nest is usually ovoidal or sub-spherical but the shape is eventually governed by the nature of obstructions in the bank. Workers carry out tiny pebbles and fine soil particles in their jaws and drop them away from the entrance. There is a space which varies in width, around the nest, but it is usually about a quarter of an inch wide. Rocks in the bank may project into the nest wall, while pebbles that are too big to carry out are sometimes simply incorporated in the nest wall. Beneath the nest small stones form a foundation which is probably unintentional, the stones being cleared of their surrounding soil in the course of growth of the nest. The clear space enables workers to move round the nest, removing earth to allow for further enlargement, and together with the foundation probably helps to move draining water past the nest.
The nest wall is composed of greyish scale-like papery material. It is closely but loosely layered and the scales continue haphazardly from one layer to the next. Together the layers form a wall varying from a quarter of an inch to one inch thick in small nests, while one large nest has been recorded from the Raglan district (Thomas) with walls one foot thick in places. This nest was situated in a tree. The papery material is brittle and is formed from chewed wood fragments. Workers will often be seen busily moving over lamp-posts and scaly barked trees collecting tiny pieces of wood with mandibles and forelegs. Once a lamp-post is established as a good source it is visited again and again. Although the scales are brittle, collectively they are resilient but are only slightly waterproof. The scales are page 30 banded in roughly a crescent manner, the bands being various shades of grey, the different colours of the bands being due to the various sorts of wood used in the making of the scales. Each band is the contribution made by a worker after a single trip. Enlargement of the nest is achieved by removing scales from the inside of the nest wall for use in the making of cells, and by addition of new scales to the outside.
Many layers or combs comprise the nest within its wall. These combs are held apart and supported by little struts which leave space enough for the wasps to move about the cells. The struts are made from rechewed nest wall paper, as are the cell walls. Growth of a nest is commonly downwards, new layers being added below the existing ones. The number of combs present in a nest will depend on how old the nest is, and the time of year will determine whether predominantly workers, drones or queens are being produced. Drone cells may be found from late February till May or June, while queens appear in April and May. There are two types of cell, the smaller ones giving workers and drones the larger giving queens and sometimes drones. These large drones are not numerous, and may not mate. An individual cell may be used several times in a season.
The cells of each comb open downwards, i.e. the bottom of each cell is on the upper side of a comb. The cells are built down as the larvae elongate, and the mouths of the cells are closed by tough silken cocoons spun by the larvae themselves. These silken cell floors are almost white in colour and are readily distinguishable from the grey walls of the cells.
Removal of a Nest
Methods of destroying nests are varied, but if the nest is required for examination, quick-acting poisons are needed so that it is not damaged. One method involves the use of chloropicrin, and is simple to carry out. but care is needed since the poison is dangerous to man. This poison is available on signature from the New Zealand Fruit Growers' Federation. It is contained in small glass phials, the tops being snipped off before insertion, neck downwards, in the entrance of the burrow. The liquid poison gives off fumes which penetrate very well indeed, accounting for all the wasps except the inevitable stragglers which, nevertheless, soon die. A sod of earth, or a sack can be placed over the hole afterwards. The operation should be done after dark with the minimum of noise and disturbance, since in summer (when most nests are located), there will often be wasps resting in the tunnel leading to the nest. After treatment the nest can be left overnight and later carefully dug out.
Preservation of a nest for examination is easy. Simply put it in a box with a loose fitting lid, and keep it in a dry place. The wasps and their larvae will dry out and shrink but otherwise the nest will page 31 come to no harm. If, however, the container is airtight the whole nest will decay. The insects themselves can be preserved in 70% alcohol.
Acknowledgement: The writer wishes to thank Miss P. M. Ralph, Zoology Department, V.U.W., for her help and advice in the preparation of this article.
Thomas, C. R., 1960. The European Wasp (Vespula germanica Fab.) in New Zealand. D.S.I.R. Information Series No. 27. 74 pp., 30 text-figs. 11 tabs.