Social caterpillars
In this scheme of classification, other non-eusocial, gregarious species of insects are referred to as presocial, subsocial, quasisocial, or in some other manner that has the unfortunate consequence of suggesting that are not quite social.
Eastern tent caterpillars (M. americanum), for example, utilize a trail-based system of elective recruitment communication that enables the colonies to exploit the most profitable feeding sites.
Passive modes of collective defense involve dilution effects since the mathematical probability that any one individual will be randomly singled out by a predator decreases with group size.
The tough silk shell of the nest formed by a colony of E. socialis caterpillars is virtually impregnable to both birds and invertebrate predators.
Indeed, the most common mode of active defense among social caterpillars is aposematic display, often combined with synchronous body rearing, flicking, and “en masse” regurgitation of toxic or unpalatable chemicals.
Studies indicate that [citation needed] the spread of alarm through colonies of social caterpillars is mediated largely by tactile and, possibly, visual cues.
Vibrational signals set up by the agitated caterpillars and propagated by the communal web would appear the most likely means of alerting the colony to danger.
Moreover, they are the only insects outside of the Hymenoptera and Isoptera to exhibit true collective building behavior involving colony-wide synchronization of activity and periodic shelter expansion.
Some social caterpillars such as Brassolis isthmia and Archips cervasivoranus employ silk to draw the leaves of their host plants into tightly bound shelters in which they rest between foraging bouts.
Unlike the complex, free-form structures of the eusocial insects, the ultimate shape that the nests of caterpillars take is determined to no small extent by exogenous factors.
The spring feeding larvae of the nymphalid butterfly Euphydryas aurinia, a non-shelter building species, bask “en masse” in the open, packing their bodies tightly together to minimize convective heat loss.
Under high levels of solar radiation on cold days, gregariousness and the darkness of their cuticle enables the larvae to gain temperature excesses (Tbody − Tambient) as great as 30 °C.
These thermal gains reported for these species appear attributable to the trapping of the metabolic heat generated by the caterpillars as they process food.
