Spiders On Ice
By Dave Anderson
Spiders On Ice
In mid-winter, I found a cluster of wolf spiders frozen beneath a cordwood pile. They crawled slowly away from exposure to light, crossing an expanse of snow. When I prodded one tentatively with a shingle of oak bark, it moved faster. Within minutes, the cold spiders retreated into dark recesses beneath a pallet.
Under the umbrella of “cold-blooded” animals, the term “ectothermy” includes creatures that use external means – sun, air or water – to regulate body temperature. Spiders use “poikilothermy” for thermoregulation. Spider body temperatures rise and fall with their environment.
How do spiders even move in winter? In one of Nature’s miracles, spiders have adapted to survive freezing temperatures by making their own antifreeze.
In autumn. spiders produce specific proteins and glycerol that confer “super-cooling” abilities, allowing cells and tissues to dip below freezing without ice forming. The adaptation is similar to those found in polar marine fishes and certain insects.
Proteins produce a thermal difference between the freezing and melting points of approximately 2°C in spider guts. Antifreeze lowers the freezing point, making spiders cold-tolerant. The substances are only found in spiders in winter. Exposing spiders to warmer temperatures results in a loss of the super-cooling ability within two weeks.
The ability of spiders to tolerate cold differs geographically. In cold regions, spiders can tolerate freezing using super-cooling abilities not observed in subtropical spiders of the same species. It appears super-cooling abilities evolved through natural selection during the expansion of tropical spiders into more northern climes.
Something Wild is a joint production of the Society for the Protection of New Hampshire Forests, New Hampshire Audubon, and NHPR. For Something Wild, I’m Dave Anderson.