#46 Browntail Moth Caterpillars
Browntail moth caterpillars have fuzzy hairs all over them, which is not at all unusual for a caterpillar. These hairs have poisonous qualities that cause bad reactions when touched, akin to touching poison ivy.
This is made worse by the fact that these hairs can detach from the caterpillar sometimes and float, unnoticed, into the air. The hairs can then land on you, triggering the reaction even if you haven’t touched the caterpillar itself!