Many spider species are known for appearing within homes, and while they are not generally dangerous to humans, pest control professionals frequently address indoor spider issues. More than 35,000 spider species have been documented worldwide, and experts agree that the number of spider species that have yet to be discovered is likely double this amount. Only 3,000 spider species have been documented in North America, and the black widow and recluse species are the only spider groups considered medically significant by most medical experts. Of the three black widow species inhabiting the US, only one, the northern black widow, can be found in Massachusetts. Black widow sightings in Massachusetts are quite rare, especially within homes, but harmful black widow bites have been known to occur on residential properties in the state. It is not uncommon for homeowners to confuse common house spiders with black widows due to similarities in appearance and web design.

Black widows are recognizable for their jet black color and the red hourglass design found on their bulbous abdomen. While this description is accurate when it comes to the inch and a half long females, male black widows are half this size, lighter in color, and they often have red or pink spots on their back. This variance in appearance makes black widows easy to confuse with many other common house spider species that can be found in the same family as black widows. This family, Theridiidae, includes American house spiders and several species of cobweb-spinning spiders that, like black widows, possess bulbous abdomens, build tattered webs in the corners of homes, and occasionally inflict painful, but usually harmless, bites to humans. According to a recent nationwide survey of pest management professionals, American house spiders and other cobweb spinners are the most commonly managed spiders within homes. This same survey had black widows as the third most commonly managed spiders, so they are far more common within homes than many people realize. The tattered webs built by most spider species in the Theridiidae family are not generally sticky enough to adhere to human skin, but they are sticky enough to catch small insect prey, such as ants and crickets.

Have you ever walked through an indoor spider web?