The caterpillars of concern to horse owners and especially breeders are the Processionary Caterpillar PC specifically Ochrogaster lunifer which has been identified as the cause of Equine Amnionitis & Foetal Loss EAFL. First observed in Australia in 2004 as an outbreak of abortions in eastern Australia the syndrome bore similarities to abortions caused in Kentucky in 2001 by the Eastern Tent Caterpillar. These PC were identified in large numbers on affected farms.
A remarkable research project by workers at the University of Queensland demonstrated that the abortions and some pre-term birth of sickly foals was related to placentitis caused by the hairs or setae of these hairy caterpillars. As the caterpillars shed their skin several times during development the dried shed skins with hairs attached build up in large numbers in the environment. Following ingestion by a mare these hairs, which carry barbs, may penetrate the gut wall, and migrate around the abdomen, piercing the uterus and placenta. The setae carry gut and environmental bacteria with them, infecting the placenta and causing a bacterial placentitis and abortion. Post- mortem sections of aborted placentae have actually shown setae embedded in them. An individual caterpillar can carry over 2 million setae and a tree containing 100 caterpillars can, via wind dispersal, contaminate an area of 4,000 square meters with 25 setae per square meter. Control is by removing caterpillar nests from stud farms, insecticidal spraying, and habitat tree removal.