Other hairy and urticarial caterpillars
Currently the only confirmed cause of EAFL is the processionary caterpillar. However, since we have not performed any experimental studies with other types of caterpillars we really dont know for certain whether other types of caterpillar might be able to cause abortion.
There are a number of other hairy caterpillars present in Australia. Some (but not all) of these are also urticarial (capable of causing itching on contact with skin). It is not clear whether the urticarial characteristics of the processionary caterpillar are associated or involved in why it causes abortion in mares.
There are several other caterpillars in Australia that have similar characteristics to the processionary caterpillar – barbed setae that can cause irritation. These include the Arctiidae (tiger moths), Anthelidae (white stemmed gum moths), Eupterotidae (Lewin’s bag shelter moths), Lymantriidae, the tussock moths (mistletoe brown-tail moths and white cedar moths).
There are also a couple of families of caterpillars that have envenomating hairs – described as tubular or porous spines that can hold a venom or irritant that is produced by a gland at the base of the hair. There are only two families of Lepidoptera within Australia that have caterpillars which possess these stinging hairs; they are the Limacodidae (“cup moths” or “Chinese junk” caterpillars) and the Nolidae (gumleaf skeletonisers).
Our observations sugges that the most common caterpillar found in the areas where EAFL cases are being found is the processionary caterpillar. Many farms do have white cedar trees and occasionally these trees get covered in the white cedar moth caterpillar. Many farms also have mistletoe in trees on the property.
It seems reasonable to be cautious and to assume that all hairy caterpillars may represent some risk to pregnant mares. Again more research is needed to determine whether other caterpillars may represent a risk to mares or not.