Stinging nettle is a plant with which it is useful to become familiar as soon as it emerges in spring because, as its common name implies, it bites back. The stiff hollow hairs along the stem and along the veins on the backs of the leaves connect to glands that contain formic acid, which is released into the skin as the tip of the hair is broken by contact. The formic acid causes a temporary, but rather uncomfortable, skin irritation. Stinging nettle is very common on moist rich soil at low elevations all across western Washington.