In Missouri alone, over forty species of caterpillars make their homes on oaks. The insects create a shelter by rolling, folding, or tying leaves together with silk or creating a silk tent that provides protection. The caterpillar Pseudotelphusa is often one of the first species to build leaf shelters on white oaks in the early summer, building its shelter by tying two leaves together. Once mature, the larvae drop onto the leaf litter below to pupate, the final stage of growth before emerging as a mature winged flying adult. Other caterpillars, including later emerging larvae of the same species, will utilize these preexisting homes and keep up maintenance of the structures.
By removing these early leaf shelters on some trees and adding them to others, with and without caterpillars, Lill and Marquis measured how the presence of shelters affected the community of insects inhabiting each tree. Comparing these test subjects with natural populations of white oaks, the researchers discovered that the removal of shelters led to a reduction of insect diversity for the entire season. The insects appeared just as attracted to oaks with artificial habitats as they were to shelters built by Pseudotelphusa.
“These shelter-building caterpillars, as the first of the season, appear to have a great influence on the diversity of similar species and could affect regional patterns of insect herbivore diversity throughout much of the broad-leaved forests of Europe and North America,” said Lill.
For caterpillars that live in shelters, the drop in available leaf-ties led to an overall reduction in their numbers. The numbers of other insect species, including beetles and non-shelter abiding caterpillars, appeared unaffected by the removal or alteration of shelters.
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