Only one species of caterpillar has been proven to cause EAFL so far. This is the caterpillar of the Bag-shelter moth called Ochrogaster lunifer. The common name for the caterpillar is the Processionary caterpillar.
Read more about processionary caterpillars here.
Other species or types of caterpillar are suspected of causing EAFL and two of these are currently undergoing testing. Many caterpillars in Australia are hairy and urticating (irritating) or venomous, so more research is needed to find out if those occurring on horse farms could cause problems.
Read more about other types of urticating and venomous caterpillars here.