And so do the spiders, the springtails, the beetles, and the wasps.
If you’ve ever been out for a walk in the woods on a balmy day in late winter or early spring, you’ve probably strolled past myriad insects and spiders making their way along the crystalline surface. Why would these creatures venture out while winter is still in the air – and on the calendar – and how do they tolerate the chilly temperatures?
Invertebrates, including insects and spiders, are cold-blooded creatures – they do not have internal regulators to help them adapt to the cold. They use other means to ensure their survival during the winter months. Some species that remain active during the winter lower the freezing point of their tissues by producing alcohols, or “cryoprotectants,” that act as antifreeze. By causing body fluids to increase in viscosity, the antifreeze reduces the cell membranes’ susceptibility to crystallizing, an event that would rupture cell membranes and result in the animal’s death.
Another method of survival employed by winter-active insects is “cold acclimation.” Metabolic changes, including the storage of energy as winter approaches, allow them to survive in the “subnivean environment,” an insulated space between the lowest layer of snow and the warmer soil. Many insects and spiders, in fact, lead relatively normal lives under the snow, consuming other invertebrates and foraging in the leaf litter for pollen or fern spores. A snowless winter means death for many insects that otherwise would be safe and warm beneath an insulating white blanket.
The reasons invertebrates make their appearances on the snow’s surface are as varied as the species. Some begin to adapt their body temperatures to the warming trend of spring.Many venture to the surface to find food – this includes springtails that can be seen near the bases of tree trunks, dining on sap and decayed plants while absorbing solar heat. Spiders prey on springtails and other insects. Yellowjackets, having overwintered in the subnivean environment, may emerge to avoid drowning as the ambient temperatures rise and begin to melt the snow near the earth. Snowflies, a species of wingless cranefly, are among the invertebrates that venture onto the snow’s surface in search of potential mates.
Perhaps your next winter or early spring stroll in the nearby woods will include a closer examination of the snow’s surface. You may be rewarded with a marching ant or two…or three…or four…