Ground nesting procesionary caterpillars are active and on the move. This period from March to June is known to be the high risk period of EAFL. It is time when caterpillars leave the nest and travel (up to 200 metres) to find a suitable place to rest underground (to pupate: developmental process to become a moth). Therefore, during this time the mares may accidentally ingest caterpillar setae (microscopic hairs) that are known to cause EAFL.
Caterpillars are usually well hidden in their nest. However, when they are at their last caterpillar stage (8th instar) they become more visible (see photo below). When you see ground nests where caterpillars are sitting on top of their frass (like the photo below), it is an indication that they will soon leave the nest.
For details on how to prevent EAFL please click here.
In the field, we have been dusting the caterpillars and inside the nest with fluorescent dust. This dust is non-toxic and it helps us track the movement of caterpillars.
Tree-hugger processionary caterpillars will remain in their nest longer than ground nesting forms. Therefore, the risk period of EAFL is approximately until end of June. Exuviae (shed exoskeleton), dead caterpillars and other nest material are often bursting out from the nest (see photo below) that is usually high up in the tree. These caterpillar remains may become airborne and dispersed further into the environment.
Please be cautious and do not stand underneath the nests.