There are more than 37,000 species of spiders worldwide, and all possess the same features that unite them with other members of arachnid family, including having eight legs arranged as two sets of four as well as lacking the antennae possessed by insects. Most spiders also possess venom.
Despite these common characteristics, spiders vary widely in terms of size, habitat and lifestyle. Borneo's tiny mygalomorph spider is the smallest spider known to scientists, and is scarcely distinguishable from a pin dot. On the other end of the scale is South America's Goliath birdeater tarantula which, as its name suggests, is large enough take on birds.
Although almost all spiders have venom, very few species possess it in concentrations that can affect humans, and even those rarely administer lethal doses. Spiders use venom to kill prey which, depending on size and species, may include flies, other spiders (even mates), fish, birds and frogs. Spiders either hunt their prey or catch them in a web.
Spiders produce various kinds of silk, and the strongest of these is comparable to the strength of steel of equal size. Different species of spiders produce different types of webs with their silk, from orb-shaped webs gracing bushes to tunnel webs blocking entrances to dark holes.