Theridiidae (cobweb spiders) in the order Araneae (spiders)
The common house spider is so common it almost doesn’t need a description. The overall color is drab: yellowish, tan, brown, or gray, with darker mottling or streaks. The abdomen is round, higher than long, usually with streaks on the side and V-shapes behind. There is usually a whitish patch just behind the highest point of the abdomen. The legs are usually ringed with a dark color.
Similar species: In North of America north of Mexico, there are more than 230 species in the same family. The common house spider is in the same family as the black widow: Theridiidae, the cobweb or tangle-web spiders, named for the messy, disorganized webs they build. This very large family is also sometimes called “the comb-footed spiders” because most species have a row of stiff, comblike bristles on the tarsal (foot) portion of their hindmost pair of legs. The spider uses these foot-combs to pull silk from her spinnerets and throw it over her prey.
Length (not including legs): 1/8 to 3/8 inch (females); 1/8 inch (males)
Most commonly seen in webs attached to garage doors, in basements and barns, between window panes and walls, and behind open doors. This is a synanthropic species: it primarily lives near humans, in our human-built habitats, and it benefits from the association. Unlike many other spiders, common house spiders do not typically flee when a person approaches; this may be due in part to their poor vision. In natural habitats, these spiders usually live in nooks on cliffs, cave entrances, hollow logs, and other solid, sheltered places.
In their webs, common house spiders capture many types of insects, including several common household pests: mosquitoes, flies, wasps, multicolored Asian lady beetles, cockroaches, and more. Once entangled in sticky silk, the prey is bitten and trussed with silk; thus immobilized, its body fluids can be sucked away by the spider. When her meal is finished, the spider cuts loose the dry, drained insect shell and lets it fall to the ground below the web, without rebuilding the web.
For many years the American common house spider was known as Theridion tepidariorum, and in the 1950s it was moved to genus Achaeranea. In 2006 it was reassigned to genus Parasteatoda. If you look in old (or older) references, you might find it listed in any of these genera. The common name of “house spider” has persisted throughout these changes, but then several other species are called “house spider,” too.
While most spiders in our temperate climate only survive for a year, dying with the first hard freeze, the common house spider, living in the climate-controlled habitat of our buildings, may survive for more than a year. As with nearly all other spiders, the ones you usually see, hanging in their webs, are females. The males are small and are usually only seen when courting or mating in the female’s web. The egg sacs of this species are familiar tan or gray dry-looking spheres, usually with a pointed or slightly elongated tip making it look rather pear shaped. Each sac can include 100–400 eggs, and a female can create more than 15 sacs during her lifetime. The hatchlings often stay in their mother’s web for several days before dispersing.
You probably have at least a few house spiders in your garage — these humble cobweb builders are very common. Take heart: they are harmless and they eat many pest insects.
Can they bite? Yes, they can, just as nearly any spider can bite, if grabbed or squeezed. Like other spiders, this species prefers to run, hide, or play dead when it feels threatened; it does not go out of its way to attack people. The bite of this species is not considered medically significant; at worst, it could be similar to a bee sting. A few people may have an allergic reaction, but in most cases the bite produces at most a painful little lump that goes away in a day or two.
In natural settings, the camouflage coloration of this spider helps it avoid many kinds of predators, including salamanders, lizards, small snakes, birds, and small mammals. In the ecosystem of a home or garage, the camouflage coloration may also help it remain undetected long enough for it to survive and reproduce the next generation of its kind.
Hummingbirds, vireos, and warblers flutter against cliff faces and the corners of buildings, collecting spider webs with which to build their nests. They also often eat the spider and egg sacs while they’re at it.
Invertebrates are animals without backbones, including earthworms, slugs, snails, and arthropods. Arthropods—invertebrates with “jointed legs” — are a group of invertebrates that includes crayfish, shrimp, millipedes, centipedes, mites, spiders, and insects. There may be as many as 10 million species of insects alive on earth today, and they probably constitute more than 90 percent all animal species.