The common house spider (Parasteatoda tepidariorum) is probably the most common spider in the world, and due to its love of hiding in human dwellings, is the most encountered by people as well. Although many millions of people are scared of house spiders, they are usually very timid, and wont expose themselves to humans intentionally.
Although house spiders might have a fearsome appearance, they are in fact harmless. They tend to always run rather than bite when faced with a larger adversary, and are more scared of humans than we are of them. Only the larger of the species could even pierce the human skin with their fangs, and their bite, although perhaps painful would not do any lasting damage.
House spiders webs are non sticky, usually sheet like and old webs are what forms cobwebs in the home. The reason that they can trap other invertebrates in their webs is that they are tightly woven, so that anything walking over the surface loses its footing and falls through. This also alerts the waiting spider who can feel the vibrations of the struggling prey. The spider itself is usually to be found inside a silken tube attached to the main web but out of sight.
Because they are one of the larger spiders in most of their habitats, they tend to rely on their webs and fangs to do the work of catching their prey rather than venom. Web spinning spiders that are large usually target smaller prey, and so unlike hunting spiders, don't need to have a powerful venom to finish the job. Also they are usually stationary in their webs, and only tend to roam around for mating purposes in the late summer.
The house spiders that tend to get themselves stuck either in the bath tub, or can be seen scuttling across the floor when you turn the lights on suddenly are male spiders. They are usually looking for a mate, which is why this encounter is most common in late summer. the reason that they also tend to run across the center of rooms rather than sneaking around the edges is simply because they are looking to find a mate as quickly as they can.
Although spiders tend to be towards the top of their food chains, there are still a few species that will feed on hosue spiders. Smaller animals such as rats and birds will sometimes catch and eat spiders, although for the most part the spiders tend to stay hidden.
Also if their web is too easily accessible to close to the ground, ants will readily raid a spiders funnel and eat anything that they find. Lastly when on the rare occasions a house spider strays onto the ground, there are many species that will make a meal out of it. these include everything from centipedes and beetles, to household pets such as dogs and cats.
A little known fact about house spiders that most people don't know is that there are actually two distinct species, the other being the giant house spider (Tegenaria duellica). The giant house spider is found only in the United kingdom, the north of France and a select few parts of the united States, which it was accidentally introduced to. It is basically the same as the regular house spider except that it has acquired the trait of gigantism over time, being the largest spider species in its native country.
Both species of house spider are known to actually have benefits beyond the fact that they will eat garden pests. The giant house spider in particular is known to kill and sometimes eat hobo and brown recluse spiders, both of which are dangerous and potentially fatal to humans. In fact because these spiders all inhabit the same niche in the food chain, wherever giant house spiders are found, recluse and hobo spider populations fall sharply, as do humans being bitten.
In different parts of the world there are many different species that are sometimes referred to as a house spider. However the most commonly referred to spiders are the barn funnel weaver spider (Tegenaria domestica), giant house spider (Tegenaria duellica) and the common house spider (Parasteatoda tepidariorum). All three species are harmless, and the differences between them are mainly concerned with their size and web structures.
The barn funnel weaver is roughly the same size as the common house spider (7-12mm), and its web is usually a tangled mess, which is usually roughly spherical in shape. The giant house spider is much larger then the other two species (18-30mm), and its web is a flat tightly woven sheet connected to a funnel. this is similar to the common house spiders web also, although the funnel is not always connected to the main web directly in the case of the common house spider.