Last spring hundreds of silk threads blocked many of the sidewalks on campus. I
watched as students became tangled in the threads. They would either freak out – thinking they had just been captured by a giant spider – or curse into their phones as they struggled to wipe silk and caterpillars from their clothes. Maybe you were one of them. Of course this was scientific observation not just for my amusement; but it was very funny. Everyday as I watched, my phone would ring with reporters and arborists wondering why there were so many caterpillars. “Are these cankerworms?” they would ask. “Spring or fall cankerworms? Will my trees die? What can I do?” The goal of The Cankerworm Project is to better understand these critters and protect trees from their feeding.
Spring cankerworm (Paleacrita vernata) and fall cankerworm (Alsophila pometaria) feed in the spring on the leaves of many different deciduous trees. In North Carolina landscapes they seem to prefer willow oak, which was the primary host on campus. Willow oak was also the tree species most heavily infested in Charlotte, Durham, and other cities. In some cases trees were 10-50% defoliated by cankerworms. Tree health could decline if cankerworms outbreak for several years in a row.
The cankerworm lifecycle has a particular weak spot we can exploit to prevent defoliation; female moths of both species climb trees because they do not have wings! Spring and fall cankerworm eggs hatch in early spring and caterpillars feed for 5-6 weeks. In October or November fall cankerworm adults emerge from pupae and climb up the trunk of nearby trees. They lay clusters of eggs in twigs then die. Spring cankerworm adults climb up trees in spring to lay eggs. They spend the rest of the summer pupating in mulch and leaf litter beneath trees.
Since the females have to climb tree trunks, we can use sticky bands to capture them on
the way up and prevent them from laying eggs. No eggs, no caterpillars, no defoliation.
Sticky bands are made by wrapping duct tape or similar product around trees and covering it with sticky Tangle Foot. Unfortunately, the efficacy of this technique is not well known. Thus, we are testing it on campus to determine if this easy, non-toxic method can help reduce cankerworm damage. We also hope to learn other things about cankerworm biology such as when adults become active and when eggs hatch. We are also interested in the predators and parasitoids of these caterpillars and their eggs.
Cankerworms and other caterpillars are an important part of urban and natural ecosystems. For example, 90% of birds feed their babies insects and insect abundance and diversity are positively related to bird abundance, diversity, and survival. Our urban ecology and pest management program tries to reduce the abundance and damage of pests while protecting the environment and people. Thanks for your interest in The Cankerworm Project. Check back for updates and don’t touch the Tangle Foot!