Buddy power warms tent caterpillars.

A new analysis of life in a tent full of caterpillars reveals more heat and more insulation than scientists had expected.

The dark, fuzzy caterpillars of the eggar moth, Eriogaster lanestris, spin silk tents where 200 or so siblings cluster between their three daily, mass forays for food. Caterpillars can bask in sunlight to soak up warmth, but most earlier studies suggested that once the sun goes down, tent caterpillars were out of luck, says Claudia Ruf of the University of Bayreuth in Germany.

Measurements that she and her Bayreuth colleague Konrad Fiedler made, however, indicate that metabolic heat of caterpillars snuggling in a tent can slowly raise the temperature some 2.5 [degrees] to 3 [degrees] C. In the April NATURWISSENSCHAFTEN, the researchers also describe their comparison of temperatures in a box containing 30 caterpillars with those in a box lacking caterpillars.

Earlier work had dismissed silk tents as insulation. However, Ruf and Fiedler noticed that when the outside temperature dropped, the inside of an empty tent cooled more slowly.

A slight boost in temperature can save days in development time, so Ruf and Fiedler propose that the warmth might have helped drive evolution of the gregarious tenting life.