The Surprising Sophistication of a Caterpillar Tent

This is the time of year when tent caterpillars make their presence known; emerging from eggs that have overwintered on tree branches, the caterpillars' first task in the spring is to create a tent.  Most people don't realize that these tents are quite elaborate solar energy stuctures that allow the caterpillars to optimize their body temperatures.
The tent of the eastern tent caterpillar is among the largest built by any tent caterpillar. The tents are constructed in the crotch of the host tree and are typically oriented so that the broadest face of the structure faces the southeast, taking advantage of the morning sun... The silk is laid down under slight tension and it eventually contracts, causing the newly spun layer of silk to separate from the previously spun layer...

Light has a great effect on the caterpillars while they are spinning and they always spin the majority of their silk on the most illuminated face of the tent. Indeed, if under experimental conditions the dominant light source is directed at the tent from below, the caterpillars will build their tent upside down...

Eastern tent caterpillars are among the earliest of caterpillars to appear in the spring. Because the early spring weather is often cold, the caterpillars rely on the heat of the sun to elevate their body temperatures to levels that allow them to digest their food... The tents act as miniature glass houses, trapping the heat of the morning sun and allowing the caterpillars to warm more quickly than they would if they remained outside the tent. Studies have shown that basking, aggregated caterpillars can achieve temperature excesses of as much as 44°C.

For a less sanguine view of tent caterpillars, see this rant at the Seattle Times.


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The whole design of the tent is all about temperature regulation. I got a before/after shot of tent caterpillars; one on a cold day, one the day after on a much warmer day (gotta love that Mid West variability).
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