The black widow spider got its name because the females sometimes eat the males that mate with them. This may also happen in other species. Each species of spider has its own way of communicating with other spiders they meet. Because of the danger of being eaten, in some species the males have special hooks on their front legs with which they hold the female while they mate. Others bring the female something to eat. There are a few species in which the male spiders construct their own little webs that are connected to the webs of the females. In these species, the male is so much smaller than the female that it would be difficult for her to actually capture the male.
Most spiders have such poor vision that they will not even notice a dead insect. Jumping spiders are one exception to this rule. They have such good vision that they can find recently dead flies or other insects to eat.
Most spiders are predators, but the jumping spider "Bagheera kiplingi" gets over 90% of its food from fairly solid plant material produced by acacias as part of a beneficial relationship with a species of ant.
Young spiders of several families feed on plant nectar. Studies have shown that they do this for long periods. They also clean themselves regularly while feeding. These spiders also prefer sugar solutions to plain water, which shows that they are looking for nutrients. Many spiders are nocturnal, they are most active during the night. The extent of nectar consumption by spiders may therefore have been under-estimated. Nectar contains amino acids, lipids, vitamins and minerals in addition to sugars. Studies have shown that other spider species live longer when nectar is available. Feeding on nectar also avoids the risks of struggles with prey, and the costs of producing venom and digestive enzymes.
Various species are known to feed on dead arthropods (scavenging), web silk, and their own shed exoskeletons. Pollen caught in webs may also be eaten, and studies have shown that young spiders have a better chance of survival if they have the opportunity to eat pollen. In captivity, several spider species are also known to feed on bananas, marmalade, milk, egg yolk and sausages.
The best-known method spiders use to capture prey is a sticky web. The placing of the web allows different spiders to trap different insects in the same area. Flat, horizontal webs allow them to trap insects that fly up from vegetation underneath, for example. Flat vertical nets allow them to trap insects in flight. The spiders that build webs usually do not see very well, but they are very sensitive to vibrations.
Females of the water spider "Argyroneta aquatica" build underwater "diving bell" webs which they fill with air and use eating their prey, molting, mating, and raising offspring. They live almost entirely within the bells, darting out to catch prey animals that touch the bell or the threads that anchor it. A few spiders use the surfaces of lakes and ponds as "webs", detecting trapped insects by the vibrations that these cause while struggling.
Net-casting spiders weave only small webs but then manipulate them to trap prey. They stretch their webs and then release them when prey strike them. Those of the family Deinopidae weave even smaller webs, hold them outstretched between their first two pairs of legs, and lunge and push the webs as much as twice their own body length to trap prey, and this move may increase the webs' area by a factor of up to ten. Experiments have shown that "Deinopis spinosus" has two different techniques for trapping prey: backwards strikes to catch flying insects, whose vibrations it detects; and forward strikes to catch ground-walking prey that it sees. These two techniques have also been observed in other deinopids. Walking insects form most of the prey of most deinopids, but one population of "Deinopis subrufus" appears to live mainly on tipulid flies that they catch with the backwards strike.
Mature female bolas spiders of the genus "Mastophora" build "webs" that consist of only a single "trapeze line", which they patrol. They also construct a bolas made of a single thread, tipped with a large ball of very wet sticky silk. They emit chemicals that resemble the pheromones of moths, and then swing the bolas at the moths. They catch about the same weight of insects per night as web-weaving spiders of similar size. The spiders eat the bolas if they have not made a kill in about 30 minutes, rest for a while, and then make new bolas. Juveniles and adult males are much smaller and do not make bolas. Instead they release different pheromones that attract moth flies, and catch them with their front pairs of legs.
The primitive Liphistiidae, the "trapdoor spiders" (family Ctenizidae) and many tarantulas are ambush predators. They lurk in burrows, often closed by trapdoors and surrounded by networks of silk threads that alert these spiders to the presence of prey. Other ambush predators do without such aids, including many crab spiders. A few species that prey on bees, which see ultraviolet, can adjust their ultraviolet reflectance to match the flowers in which they are lurking. Wolf spiders, jumping spiders, fishing spiders and some crab spiders capture prey by chasing it, and rely mainly on vision to get their prey.
Not all spiders use silk to net their prey. Instead, these spiders may capture insects by grabbing them and then biting them. Among these kinds of spiders the two best known are the wolf spiders and the jumping spiders.
A wolf spider will usually wait until an insect comes near to it, and then rush at the insect, grab it using its front legs, and then bite the insect so that its venom can do its work.
Female wolf spiders lay their eggs on a pad of silk and then draw the edges together to create a round ball that they carry along with them wherever they go. They hold their egg balls to their tail ends by using their silk. When the eggs hatch, the little spiders will crawl onto the mother's back, and she will carry them along with her for days or weeks.
Wolf spiders are very good mothers and will strongly protect both their egg balls and their infants. When the time comes, the little spiders will leave the mother and each will go its own way.
Jumping spiders have very good eyes and can see well. They sneak as close to an insect as they can, and then they jump onto the insect and immediately bite it. Since they often hunt in trees, bushes, and on the sides of walls, if the jumping spider misses it may fall off. But they have a way to save themselves from harm. Before they jump they fasten their silk to the place where they have been standing, and as they jump they let out a silk safety line. So if they fall they will catch themselves when they reach the end of their silk safety line. Sometimes a jumping spider will catch an insect and then fall while still holding onto the insect. But the spider is still safe.
Jumping spiders make little silken "tents" for themselves to sleep in. When they lay eggs they keep them inside such a shelter. They do not take their eggs with them when they go out to hunt.
For all male spiders it is dangerous to seek a mate. The female spider may not realize that the male is a spider of her kind, so she may try to eat it. The jumping spiders not only have visual patterns that identify them to each other, but the male jumping spider will do a special dance when it approaches a female of the same species. That way, the female can recognize that it is a male of her species. She will generally forget about eating for long enough to mate with the visiting male spider.