Wasps and Winter (Hibernation)

With temperatures dropping and daylight decreasing, the regions wildlife has already begun to brace itself for the long winter. Whilst amphibians, reptiles and mammals like hedgehogs are mostly all still active throughout September, many species of insect have started to enter torpor. Some of the valleys on the southern edge of the North York Moors had frost (on the morning of the 19th) recently. Frost is often a catalyst for many small animals to enter hibernation, as it reduced food availability, decreasing temperatures and hours of daylight, the one which is most significant to a species depends what the species is. Wasps for the most part tend to enter hibernation long before the first frost appears on the ground. It is only the fertile female "Queen" wasps that hibernate, once they have mated in late summer there is little need to be active, as they will not begin to build a nest and form a colony until the following spring. When fertile queens are produced (which ultimately decides when they hibernate) is governed by the amount of sperm the queen has, usually sometime in mid-late summer. Queen wasps mate once, store the sperm and use it through the following year to create a colony, as it begins to run low, the queen begins to produce fertile males and females which leave the colony and breed. Males die soon after breeding but females enter hibernation (as mentioned above).

 

This Queen  Dolichovespula media (Median Wasp) was found under a well decayed hawthorn log on the edge of what is quite a productive area of oak woodland for invertebrates, in the Scarborough area. D.media is a recent colonist of North Yorkshire (and Britain). A species which I first recorded in 2008 (one of the first North Yorkshire records). These impressive social wasps are second only to hornets in size in Britain, and queens have quite elaborate brown markings around the thorax, as can be seen in the photo. Dolichovespula (of which there are 3 species regularly encountered in Britain) tend often to hibernate within rotten wood, whether it be in a tree hole or under a log (like this one), they will occasionally overwinter in a building like a shed, like the more common Vespula species.  Social wasps (and bumblebees which have a similar stratergy) often overwinter on north facing aspects, which retain a more stable temperature and are not excessively heated by the sun.

Hibernating wasps adopt quiet a characteristic position, which can be seen in the photograph above, in which the antenna and wings are tucked below the body and held by the middle pair of legs. This is primarily done to protect them. The front pair of legs are also tucked below the body. The hind legs are usually used to keep the wasp in an upright position and are left untucked (not seen in my photo). The water dropplets are due to condensation, as the wasps body is colder than the surrounding air. Wasps like many other animals suffer high rates of mortality over the winter, however this is not always directly linked to cold winters. Warm winters pose numerous problems to hibernating animals, in that they regularly wake up and use valuable body fat reserves, especially if temperatures fluctuate. A warm spell followed by a cold one can have very negative implications in some situations. So in some ways a stable cold winter can be quite beneficial.  Regardless of the cold the biggest killer of wasps over winter is probably predators including ground beetles, centipedes and birds like great tits, which often roost in similar situations to where wasps hibernate.