Speaking from recent experience, beware these caterpillars which have infested Maine and other parts this summer. Browntail caterpillar hairs are toxic with toxicity lasting 3 years. Hairs are easily airborne from shedding, raking, mowing and cause a poison ivy rash (only worse) and respiratory distress if breathed. Found in hardwoods - red oak (did a number on oaks here), apple, birch.
A browntail moth caterpillar Maine Department of Agriculture, Conservation and Forestry. Note two dots on tail end.
Hairs on adults are supposedly not toxic but may have residual cat