As my wife and I sat outside, late last year, enjoying a glass of wine, or three, we noticed far fewer wasps pestering us. I decided to learn more about this much maligned insect.
There are 9,000 wasp species in the UK, of which 70% are parasitic. Our two commonest species of “social wasp” are the Common wasp (Vespula vulgaris) and the slightly larger German wasp (Vespula germanica).
At the beginning of any year, the queen wasp hibernates in a protected site, such as a shed, loft, or underground. Cold winters suit her best. If temperatures rise too much she may wake up, and then starve if there is not a supply of early nectar. When finally waking in the Spring, she finds a dark, dry warm place to build a nest. Stripping wood with her mouthparts, she mixes it with saliva to make pulp. Building a central support pillar which is covered with a chemical to repel ants, she then makes a single hexagonal cell. Constructing six cells around this, a larger hexagonal shape is created. The nest is extended to about 25 cells, placing a single egg in each. These eggs are fertilised by sperm stored since the previous Autumn, in a sac (spermatheca) within her reproductive tract. Wasp eggs take 5-8 days to hatch into larvae. The larvae are fed nectar and small insects by the queen, and develop into pupae in about two weeks. The adult wasp emerges 8-18 days later. These wasps are worker wasps, and are all sterile females. The workers are responsible for food foraging, feeding the next batch of larvae, and general nest DIY. As worker wasp numbers increase, more nest building takes place. The queen produces about 300 eggs each day.
In a year of suitable weather, the Common Wasp (Vespula vulgaris) can build a nest the size of a football, containing over five thousand wasps. The German Wasp (Vespula germanica) nest is smaller, often built in a bush. Each nest has an outer shroud with lots of air spaces for insulation. If the nest is underground, the worker wasps collect water, mixing with soil to make pellets. These pellets are removed to make more space for the nest. If the nest is in a loft space, the temperature within the nest can become hotter than the ideal 31 degrees centigrade. The worker wasps collect water and spray it inside the nest to assist cooling. This can lead to a stain on a ceiling or wall, within a house.
Wasps are carnivorous, killing an enormous amount of caterpillars, greenfly and aphids to feed the larvae. It is estimated that in the UK, social wasps kill 14 million kilograms of insect prey each year. The larvae reward the workers by producing a rich, sugary, creamy blob of “pre-digested soup”. This is mainly produced from chitin (insect shells). This high energy feed, and plant nectar is all that the adult wasp can eat, due to their wasp waist and lack of digestive enzymes. The worker wasp lives only about three weeks. They follow each other to a good food source, but cannot communicate like bees. They have no food store, such as a bee’s honey and pollen, so wasps have to search for food daily, to supply the larvae. In a wet summer this is a problem.
In late summer, early autumn, the last batches of larvae are growing. These are to develop into fertile wasps. The fertile males (drones) develop in worker cells, but the fertile females (queens) develop in special large cells near the base of the nest. There could be one to two thousand queens in each nest. The larger queens force the drones out of the nest, and they have to find enough nectar to keep going until the queens emerge, and they can mate. The queens hang around in the nest, finding bits of food and laying down fat for the winter hibernation.
Whilst all this is going on in late summer, the workers find that they have no larval mouths to feed. This means that they cannot get a “fix” of rich sugar, to which they are addicted. They collect nectar from late season flowers, but this is poor quality, and their energy levels drop. Sensing a glass of wine, or jam doughnut, they can cause constant harassment to the owners of the said treats, as their desperate urge for a sugar fix continues.
So why the fewer numbers of wasps in 2021? The early months of the year were mild, causing the loss of queens which awoke too early and starved. These queens were already less in number due to the same problem in early 2020. The month of June was very wet, causing a huge problem for workers to collect enough small insects to feed to larvae.
2022 has started off badly for wasps as it has been too mild, causing the death of many queens due to starvation. A warm dry summer would boost the size of the nest and numbers of wasps within.
So, if you do get pestered by homeless, sugar junkie wasps this Autumn, smile don’t swear. Remember how useful they are in nature.