The species Phereoeca uterella, also known as the plaster bagworm or household casebearer, is a moth found in warm, humid areas across the U.S. Its bite can leave behind tiny hairs, about the size of a needle, that cause bruising and itching.
According to Wikipedia, Phereoeca uterella larvae live inside flattened sheaths made of silk mixed with sand, dust, or soil. Their cocoons have openings at one or both ends to allow the larvae to move partially out when searching for food.
The bruises from their stings can last for weeks, with swelling, pain, and itching. Applying anti-itch creams can help ease symptoms. These larvae, about 13 millimeters long, can lay up to 200 eggs per cycle. The eggs hatch into cocoons hidden in warm parts of the house.
They also feed on fabrics and sometimes cling to spider webs, as they prey on small spiders. Since they thrive in warm indoor spots, it’s important to regularly inspect hidden corners of your home, especially the warmer areas, to keep them in check.