Here in my yard in Lew, One of there favorite species of trees is crab apple and my neighbor had a fairly big nest in his tree this spring, When the larvae hatch and they leave the nest, It releases all the toxic hairs into the air as well as when the caterpillar moults into a moth, It leaves behind the carcass, I had several on my foundation but thought nothing of it not having to deal with them before but quite aware now.