Life History
Life History
Of the thousands of species of wasps in the British Isles, only thirteen live together in colonies. These are the social wasps and two of them are particularly common in the UK, especially in the south. They are the Common and German Wasps – Vespula vulgaris and Vespula germanica.
Although both species will nest in cavities such as roof spaces and garden sheds, their preferred situation is underground, accounting for around 70% of wasps’ nests in Britain.
The wasp year begins in early spring – as early as March in southern England since winters have become milder.
New queens emerge from hibernation in response to increasing daylength, coupled with rising temperatures.
Each queen searches for a likely nest-site. She is attracted to dark spaces, such as rodent burrows in the ground, crevices in brickwork, or gaps under roof tiles.
If there is sufficient space within, she will start building her nest.
The process of nest-building by wasps is entirely different from that of bumblebees and honeybees, the most obvious difference being that social wasps build their nests out of paper, made from wood scraped off dead trees and fences, whereas bees use wax secreted from their own bodies.
The embryo nest is about the size of a golf ball and is of a uniform colour: grey in the case of the German Wasp and a sandy colour in the case of the Common Wasp.
This uniformity is due to the fact that it is initially only the queen that builds the structure, and she tends to use the same source of material each time.
The Common Wasp uses soft, rotten wood, whereas the German Wasp uses tougher, firm wood.
The embryo, or queen, nest eventually consists of around 50 rigid, hexagonal, downward-facing cells, surrounded by a more fragile covering called the envelope.
By the end of April the eggs laid by the queen (one in each cell) have hatched and developed into larvae, which the queen feeds with the chewed bodies of insects and other arthropods.
Each larva is a cream-coloured, rather ugly, grub with a distinct orange-tinged head. As it faces downwards, it has to brace itself against the sides of its cell, using an adhesive fluid in the early stages, but swellings on its body as it grows larger.
As with all insects, wasp larvae have to shed their skins at intervals to allow for growth. After five of these changes, the larvae become fully grown and fill their cells completely.
At this stage they stop being fed by the queen and they spin a covering of white silk over the top of their cell, before changing from larvae to pupae.
Each pupa looks very like a wasp, but is creamy-white at first, becoming progressively more pigmented towards the end of this so-called ‘resting’ stage, which lasts about a week.
The pupal skin then splits open to reveal an adult, female, worker wasp.
After one to two days resting in her cell, the young worker softens the silk cell cap with enzymes in her saliva, then cuts her way out of the cell, using her toothed mandibles.
For the first few hours she is pale-coloured, but she soon darkens into the familiar black and yellow.
Almost immediately the first workers begin to help the queen by distributing any food she brings back to their sister larvae.
A few days later the first workers give up nursing duties and venture out of the nest to begin foraging. Depending on the immediate needs of the growing colony, foragers gather water, wood-pulp for nest construction, chewed insect protein for the larvae, or sugar as an energy source for the queen and the nursing workers.
Each worker takes about three to four weeks to develop from egg to foraging adult.
Once the first workers begin to forage, the queen can stay inside the nest and devote her time to laying eggs.
The workers take over all other duties, including the building of new cells for the queen to lay eggs in.
The colony now increases in size rapidly and can ultimately contain over 5,000 adult wasps at any one time.
Over the course of the summer a nest of either species may produce a total of 30,000 wasps.
Up till now, the eggs laid by the queen become workers (all female).
Around 500 male wasps and new queens are produced by the old queen.
If the queen withholds her stored sperm, the eggs she lays are unfertilised and have just one set of chromosomes. They develop into males.
If she allows some eggs to be fertilised, these eggs have two sets of chromosomes and are laid in special cells, larger than the normal ones. The workers only construct these ‘queen cells’ towards the end of the season.
The developing larvae in these larger cells are fed more than their smaller sisters, so grow bigger and become queens.
The new queens and males fly from the nest to mate some distance away. This exodus appears to be synchronised, so that queens and males from all the local nests appear at the same time. In this way inbreeding is usually avoided.
Mating takes place on the ground or in a tree. Queens only appear to mate with a single male, but once he has mated with her, he flies off to find other, unmated queens.
After mating, the new queens feed on nectar from late-flowering plants (such as ivy) to increase their body mass before they look for a place to spend the winter. The nectar is converted into fat and stored in their body tissues.
Decreasing day-length, rather than temperature, is probably the main stimulus that urges new queens to search for a hibernation site.
Each queen seeks out a dry, cool situation in which to spend the winter. They can often be found in spare bedrooms where the heating is rarely on.
Hibernating queens adopt a very characteristic pose. Hanging on to a rough, vertical surface with their jaws, head upwards, they tuck their legs in and bend their antennae under their head, between their front legs. The wings tips are pressed down under the rear of the body.
Like this, they remain immobile for around six months, unless the temperature of their hibernating site rises significantly – such as happens if we turn on the heating in a spare room. If this case, wasps are roused from hibernation and are likely to fly away. This is why we sometimes find queen wasps buzzing around in our homes in mid-winter. In such circumstances, they lose valuable energy and are unlikely to survive the winter, even if they do find their way back, or locate another suitable space.
Of the 500 or so mated queens produced in each nest, only one per colony needs to successfully establish a thriving nest in the following year to maintain the wasp population at the previous season’s level.
Many hibernating queens die before they have a chance to establish their own colonies. There are various reasons for this: mild, damp winters can encourage parasitic fungi to attack and kill the queens; unseasonably high temperatures can arouse the queens, causing them to use up energy stores; extended periods of excessively cold weather can kill queens; mice, rats and other predators will eat hibernating queens.
Even if they survive the winter, new queens face many dangers until they have successfully raised the first batch of adult worker wasps: the queen may choose an unsuitable nest site that floods with the first wet weather; for around six weeks the queen puts herself in danger of injury or death as she makes frequent foraging flights every day to collect wood-pulp, water and food; periods of cold, wet weather in April can kill off colonies, even once the first retinue of workers have taken over foraging duties.