Leaftying caterpillars that attack white oak, Quercus alba, use silk to tie together two leaves to form a “leaf sandwich” or leaftie within which they feed. Because leaftying caterpillars are small when they first eclose (<1 mm in length), they apparently require touching leaves in order to construct their leafties. We first show that saplings of Q. alba vary greatly in the degree to which leaves are spatially distributed throughout their canopies, i.e. percent leaves touching varies from 4% to 36% per plant. We then tested the hypothesis that this difference in plant architecture, in the form of the number of touching leaves, influences the abundance of leaftying caterpillars and the amount of damage they cause. First, surveys of all leaves on a set of non-experimental saplings showed that trees that naturally had more touching leaves had a greater number of leafties. Second, we increased the number of touching leaves by tying together bases of leaves around branches, and compared subsequent colonization by leaftying caterpillars on these experimental branches with colonization on similar but unmanipulated control branches. Experimental manipulation increased the number of touching leaves, leaftying caterpillars, and leafties, and increased damage by this guild of insect herbivores. Together, these results suggest that architectural traits that minimize leaf-to-leaf contact in Q. alba may be defensive traits against leaftying caterpillars.