Cobweb spiders (family Theridiidae) are a large and diverse family that includes the black widows, false widows, and many small, harmless species responsible for the tangled, irregular webs ('cobwebs') found in corners of rooms, garages, and outdoor structures. Arizona is home to dozens of Theridiidae species beyond the medically significant black widows. Most cobweb spiders are small (1/8–1/4 inch), round-bodied, and build irregular three-dimensional webs in sheltered locations. They are completely harmless and are among the most common indoor spiders in Arizona. The family name comes from the characteristic tangled, irregular web structure — unlike the organized orb webs of garden spiders or the sheet webs of funnel weavers.