The bristly hairs on the White-marked Tussock caterpillar sting when touched, causing pain, redness, irritation, and hives. Contact with these urticating hairs should be avoided. The caterpillar changes colors, but the features are consistent throughout the species, and the coloration is always bright and alarming. Four tufts, or tussocks, of dense hairs look like bumps on the 'back' of the caterpillar. These may be white, gray, or yellow. A bright red collar sits below the red or brown head. Long, black lashes, about 2.5 cm (1 inch) long, extend from either side of it. Another set of long, lash-like hairs extend out from the rear end and may be black, or brown and black. Fine, wispy black hairs are hard to see, but they cover the whole length of the body. White spikes of hair stick out in clumps on the sides of the body. A solid black line runs down the 'back' with a bright yellow line on either side of it. Two small, bright red dots appear near the rear end.
Groups of these caterpillars are often found crawling on trees. Wads of stinging woolly hair may also be nearby, which are cocoons of caterpillars that are already pupating. Larvae chew up leaves to the point of leaving only the veins behind. Collectively, a group can defoliate a young tree, putting it under severe stress, but mature trees can generally withstand the leaf loss. Caterpillars are most often seen in the middle of summer on all sorts of deciduous trees. They are active, and can cover quite a distance from where they hatched to where they eventually pupate.
Adult male moths are gray with a white mark on the lower, inner edge of each wing. Females are also gray, but have stunted wings that are barely visible, and are unable to fly. Foamy bubbles accompany the eggs as they are laid in a large mass on tree bark. Two broods can be produced each year.
The map above showcases (in blue) the states and territories of North America where the White-marked Tussock Moth Caterpillar may be found (but is not limited to). This sort of data can be useful in seeing concentrations of a particular species over the continent as well as revealing possible migratory patterns over a species' given lifespan. Some species are naturally confined by environment, weather, mating habits, food resources and the like while others see widespread expansion across most, or all, of North America.*NOTE: States/Territories shown above are a general indicator of areas inhabited by the White-marked Tussock Moth Caterpillar. Insects generally go where they please, typically driven by diet, environmental changes, and / or mating habits.