Season’s greetings readership,
As I type, millions of Vespula vulgaris (‘common wasp’) queens are in a deep slumber within dead logs, sheds, attic spaces, burrows, and innumerable other areas out of the British elements. Because all other members of a wasp colony die over winter, the survival of the queen is vital to regenerate populations in the spring and summer. But this process is far from simple, incorporating physiological and behavioural adaptations that must be timed accurately to prevent freezing, parasitism, predation,and starvation. The journey of a queen wasp is quite an incredible one involving death, opposition, sex, family, altruism, resurrection, and prejudice, and I would like to personally recommend it as a superior alternative to the biblical prose to which we are flooded at this time of year.
As autumn really kicks in, food availability falls to levels insufficient for wasp colonies to survive and workers gradually die off. Drones (males) live for some time longer, searching for queens to mate with, but they too perish during the first frosts of the winter. The mated queens are all alone in their micro-worlds, their family starved or frozen to death, and a long, hard winter follows. To shamelessly anthropomorphise, the situation seems almost post-apocalyptic from a queen’s perspective. Their prospects don’t look good, but several key adaptations ease the struggle for survival.
The first is their ability to find and embed themselves in an appropriate hibernaculum (the place they lay dormant). This is more complex than it sounds. Hibernacula must meet specific criteria to benefit the queens. The most important feature is that they must insulate the queens from the cold and the required level of this insulation varies with the minimum temperature reached in the vicinity over the winter (Barnes et al., 1996). For example, queens in subarctic Alaska will need a great level of insulation and may be covered by 15cm of dead leaves and 60cm of snow, whereas those dormant in rural Devonshire may be amply insulated under a log pile or some tree bark. However, it is also essential that these areas be dry. Dank areas will more readily harbour entomopathogenic (insect-killing) fungi that would infect and slowly annihilate a dormant queen (Harris et al., 2000). In addition, moisture in damp areas may freeze and form ice crystals, penetrating the body of the queen, killing her. Good hibernacula are therefore quite dry and insulated – e.g. deep inside a log pile, underground or in an artificial structure.
But alas, no matter how well these hibernacula are chosen, the temperatures will still drop to well below zero, which is enough to kill many animals (Barnes et al., 1996). Indeed, the body temperature of the queens can drop to as much as -24oC without ice forming. This is a process called supercooling. Though the exact mechanism that allows V. vulgaris queens to lower the freezing point of their tissues is not known, other insects use a combination of antifreeze glycoproteins, salts, glycerol, reduction in ice nucleating agents (the nuclei around which crystals form), and dehydration of the body (e.g. Sformo et al., 2010). These antifreeze glycoproteins actively inhibit ice formation by binding to small ice crystals (adsorption-inhibition mechanism) in the haemolymph and body tissues, preventing further crystallisation and damage to cells (Devries, 1971); salts and glycerol depress the freezing point by disruption of hydrogen bonds between H2O molecules when in high concentration. In other insects, severe dehydration of the body takes place, which increases the effective concentration of salts, small osmolytes, and antifreeze proteins. Some even stop feeding and evacuate their gut contents as a way of reducing ice nucleating agents! It is almost certain that queens utilise more than one of these techniques, but the run-up to winter is likely an important period to begin production of freezing point depressive compounds and perhaps dehydration of the body water.
Once temperatures are sub-zero and the queen is curled into her characteristic dormancy stance, she must wait until spring. This dormancy period varies with the length and severity of winter, emerging in early May in Alaska (Barnes et al., 1996), but even as early as mid-March in Southwest England (personal observation).
But remember, on her intrepid quest for a good hibernaculum and her slightly less intrepid quest for a deep slumber, there are a whole host of predators that would kill (if not eat) her. Even once she has found an ideal spot, many other animals are searching for dry, secluded locations. Centipedes, spiders, many bird species, badgers, numerous rodents, various parasitic Diptera and Hymenoptera, and Varroa destructor mites will all feed on an active or inactive queen (Fox-Wilson, 1940). It is because of this that most queens do not survive the winter. But the fabled sting, like a mighty spear of vengeance, may be her saving grace. Even in their dormant state, queens can administer venom in admirable quantities (personal observation)! This likely deters some mammalian and avian predators during the queens’ dormancy, but invertebrate predators will still take the opportunity to feast upon her flesh.
Though the process of overwintering is fraught with a medley of dangers – biological and physical – one of the most important aspects governing survival for queens are their fat reserves. Through the summer, queens in their larval stages are being fed by nurse workers (their sisters). It is likely that some fat stores are retained after pupation and further accumulated by the new queen after she emerges from the nest (Harris and Beggs, 1995). This is especially true in the later stages of the season, when the colony begins disintegrating, but the new queens remain active and forage for some time longer. It has been shown that fat reserves are the most important physiological variable governing queen survival during overwintering (Harris and Beggs, 1995). They require these reserves to not only allow them to subsist over winter but to fuel flight and foraging shortly after emergence from a hibernaculum. In addition, early in the season, queens will often usurp one another in vicious, brutal duels where the winner assumes control of a nest; though untested, it is possible greater fat reserves enable more usurpation attempts or an improved fight performance straight after spring emergence.
After such a traumatising winter, most queens will be dead, having been devoured by parasites or predators, frozen due to poor hibernaculum selection, or starved because of inadequate fat reserves. Some estimate V. vulgaris queen survival during the winter to be as low as 2.2% (Archer, 1984). But from the depths of a log pile, rises a brilliant yellow-black phoenix of natural selection and chance. A queen. As she warms her flight muscles and readies herself to establish her reign over the land, her body calls out for nourishment. The queen takes flight towards the nearby Camellia flowers. Lo! Behold! There is a final hurdle the queen must navigate before she can begin establishment of her queendom. An angry, unenlightened gardener approaches! With a rapid change of direction, the queen deftly avoids the lumpen fist of the maladroit gardener, and instead takes flight towards the daffodils many metres away. A quick intake of nectar and pollen and her energy levels are sufficient. She can now begin constructing an ecologically dominant force in the area. She has survived.
The slaughter of queens in spring by people is highly adverse for both parties. Though everything about wasps says “stay away”, as cognisant beings we are able to judge that wasps are vastly beneficial*.
So, as you go about your Christmas cheer this month, remember the plight of the wasp! The incredible journey they make is biblical in scope and effort – full of perils, as close to resurrection as is biologically possible, disaster, death, but ultimately resulting in life (and is far beyond my writing skill to do it justice). What more could you possibly want?!
Until next time.
* For an explanation as to why wasps are beneficial please take a look at this blog post from last year.
Featured photo: Vespula vulgaris queen on the hand: Alex Dye, an amazing human and entomologist in every way (@AlexLikesFlies)
Wasps emerging gif: https://forums.warframe.com/topic/130579-gif-thread/?page=216
Dormant wasp: http://www.arkive.org/common-wasp/vespula-vulgaris/image-A8785.html
Queen wasp sting: https://commons.wikimedia.org/wiki/File:Sting_of_Queen_Wasp.jpg
Archer, M. E. (1984) Life and fertility tables for the wasp species Vespula vulgaris and Dolichovespula sylvestris (Hymenoptera: Vespidae) in England. Entomologia generalis, 9, pp. 181-188.
Barnes, B. M., Barger, J. L., Seares, J., Tacquard, P. C. and Zuercher, G. L. (1996) Overwintering in yellowjacket queens (Vespula vulgaris) and green stinkbugs (Elasmostethus interstinctus) in subarctic Alaska. Physiological Zoology, 69(6), pp. 1469-1480.
Devries, A. L. (1971) Glycoproteins as biological antifreeze agents in Antarctic fishes. Science, 172(3988), pp. 1152-1155.
Fox-Wilson, G. (1946) Factors affecting populations of social wasps, Vespula species, in England (Hymenoptera). Proceedings of the Royal Entomological Society of London. Series A, General Entomology, 21, pp. 17-27.
Harris, R. J. and Beggs, J. R. (1995) Variation in the quality of Vespula vulgaris (L.) queens (Hymenoptera: Vespidae) and its significance in wasp population dynamics. New Zealand Journal of Zoology, 22, pp. 131-142.
Harris, R. J., Harcourt, S. J., Glare, T. R., Rose, E. A. F. and Nelson, T. J. (2000) Susceptibility of Vespula vulgaris (Hymenoptera: Vespidae) to generalist entomopathogenic fungi and their potential for wasp control. Journal of Invertebrate Pathology, 75, pp. 251-258.
Sformo, T., Walters, K., Jeannet, K., Wowk, B., Fahy, G. M., Barnes, B. M. and Duman, J. G. (2010) Deep supercooling, vitrification and limited survival to -100oC in the Alaskan beetle Cucujus clavipes puniceus (Coleoptera: Cucujidae) larvae. The Journal of Experimental Biology, 213, pp. 502-509.