Caterpillars of the oak processionary moth can cause potentially severe and even deadly allergic reactions.
Long white hairs released by caterpillars can cause allergic reactions in people who are allergic. Reactions can range from skin and eye irritation, to difficulty breathing and even anaphylactic shock “At best, you can get contact dermatitis. At worst, you can die,” says Jason Dombroskie, manager of the Cornell University Insect Collection and coordinator of the Insect Diagnostic Lab in Ithaca, N.Y. “You can go into anaphylactic shock and have your airways close up. The airborne hairs set up a whole different ballgame,” he said.
According to Kobus Erasmus on the website of the Hoedspruit Endangered Species Centre (HESC) in Mpumalanga, these caterpillars are found crossing roads and pathways in a single line where they follow each other in a head-to-tail procession. Some of these processions have been known to consist of up to an astonishing 600 caterpillars.
The larvae are more conspicuous than the adults due to their gregarious behaviour. They are quite hairy and form these congregations to ward off predators and find food and it appears that they feed on a wide variety of plant species. As they usually get together in very large numbers, they easily strip the host tree of all its leaves. However this is a natural phenomenon and trees perfectly capable to recover without any long-term damage having been done.