Thanks to Aydin Örstan for teaching me a new word. He explains it in this post. I also found a detailed explanation, along with more information than the average person will ever need to know about woodlice, ("roly-polies"), on this web page:
"Thigmokinesis is a characteristic response of the cryptozoa (animals living in soil and litter) and has been carefully investigated in woodlice by Friedlander (1963). The response is such that the animal is most active when the contact with the substrate is minimal—that is, when only the feet are on the ground. As soon as other parts of the body touch a surface the animal slows down and may stop if enough of the body makes contact. Thigmokinesis causes woodlice to congregate in crevices between stems of grass or leaves in the litter where they are protected against desiccation and predators. Even other woodlice qualify as solid objects, so that thigmokinesis contributes greatly to the build up of aggregations.
Aggregation is one of the most characteristic forms of woodlouse behaviour and is probably, to some extent, a purely accidental result of individuals acting in the same way to the same stimuli, with thigmokinesis as a prime cause. What biological significance aggregation may have is uncertain and needs investigation. It is known, however, that bunching reduces individual water-loss...."
*This does not mean I will be posting a new word every day.