Winter’s Tales in the Insect World

Ruffled and stung by a sharp, icy wind, I decide to turn back. The watery yellow light on the horizon is threatened by thick grey clouds, which seem to be dragging an early evening in their wake. Prickly lines of hawthorns are strung out in lines across the bare fields.

A tiny spot of red, stands out against the pale brown of a dried tall grass; nestled in the crook of the bent leaf are a small cluster, or aggregation, of five Coccinella septumpunctata, the 7-spot ladybird. I don’t envy the winter ahead for these hardy little beetles, but they have a few survival tricks under their wings. The secret is in a suite of anti-freeze compounds which accumulate in their body as the days get colder, particularly glycerol, a sugar alcohol. If you asked them what their superpower was, this would be it; and appropriately enough, it is called supercooling, and allows them to withstand temperatures several degrees below zero.¹ They are not, however, invincible: cold enough temperatures (the ‘supercooling point’) will kill them, although as winter progresses, this point gets lower.²

I hurry on, as much as the squelchy ground will let me, edging closer to the hedge where the sloping ground is drier to avoid jumping puddles. Not everyone has the ladybird’s cold temperature abilities, and some well-drained, even-temperatured underground spot could be just the place to sit out winter. I know that down there, somewhere, a remarkable little winter scenario will be playing out: the female common earwig, Forficula auricularia, will be in a burrow, having mated and dispensed with her mate’s help, and be showing an astonishing amount of vigilance in guarding the several dozen pale oval eggs she has laid, regularly licking them clean from fungus to increase the chances of survival.¹ I wish I had a window to glimpse into that world.

Jackdaws and rooks swirl and call overhead, but I can’t even see the gnats that persist into winter today, and it is over a month since I last saw hover flies feeding on ivy flowers, or a large queen bumblebee searching, somewhat late, for a hole in which to hibernate. Being active through the winter months isn’t everyone’s thing.

A lot, like the earwig, head underground, but for many, they spend the winter months in diapause, a state of physiological change in their bodies which stops development for a while, and so prolongs survival, a particularly useful trick if your lifecycle is short, food is scarce, and you only fit one generation into one year. There is not a single mechanism that makes this happen: different mechanisms point to the fact that different species of insect developed the same solution to a common problem, but their bodies found a variety of ways to get there. Generally speaking, hormones are involved, and these are triggered by a combination of genetics and a number of environmental factors: day length and change in temperature are particularly important ones.³ Ladybirds do it; bumblebees do it; but others enter diapause as larvae, pupae, or even eggs.

Closer to home now, my route takes me through a graveyard, full of Victorian gravestones. The sculpted pupa of a small white butterfly, Pieris rapae, green with black flecks, is attached by a silken thread to the weathered face of an old stone. The process of reorganising its body from caterpillar to butterfly inside the pupa is one that can potentially last just a few weeks, but this one is in diapause. Metamorphosis has temporarily stopped, but when diapause ends, normal business will be resumed; but now instead of just weeks, the whole stage lasts about eight months.

As I reach home, I notice the large oak tree seems to have lost its leaves overnight; the underside of many are speckled with little dark red, raised spots. I can’t resist picking one up. This has got to be, in my opinion, one of the best winter’s tales in this neck of the woods: inside, a tiny wasp is developing. The spot, a spangle gall, grew as a result of the interaction of the chemicals from the mother and the plant itself. She laid her egg, inserting it inside the leaf itself, and as the larva hatched, the gall grew around it, providing it with food and protection. Safety is not totally assured, though, for this diminutive, round, black wasp, Neuroterus baccarum, as other species of wasp like to take advantage of this pre-packed snack capsule, and lay their eggs through its walls. At least, though, they do not hunt out the galls once they have fallen to the ground.⁴ The Neuroterus baccarum’s spring and summer tale also does not disappoint, but that’s another story.

I employ my winter strategy, and head indoors.

By Chloe Aldridge

References

1. Gullan, P.andCranston, P. 2014. The insects – an outline of entomology. 5th Chichester:Wiley Blackwell.

2. Barron, A. and Wilson, K. 1998. Overwintering survival in the 7-spot ladybird, coccinella septumpunctata (coleoptera:Coccinellidae). European Journal of Entomology, (95), pp. 639-642.

3. Chapman, R.F., Simpson, S.J., Douglas, A.E. 2013. The Insects – Structure and Function. 5th Edition. Cambridge: CUP.

4. Askew, R. The Biology of Gall Wasps. [On-line]. Available from: http://www.nhm.ac.uk/resources/research-curation/projects/chalcidoids/pdf_Y/Askew984b.pdf [25 November 2015].

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