Spiders are not insects because they have eight legs instead of six and two body segments instead of three. There are some other interesting differences too; one such example is that because spiders lack extensor muscles in their limbs, which most insects have, they use hydraulic pressure to extend their legs.
All known species of spiders except for one are predators, mostly preying on other small insects, although a few species are known to take on small birds, lizards, and fish. Most species use various forms of webs to trap their prey, but many species use other methods to capture their prey; some actively run after their prey, such as the jumping spiders and wolf spiders; some species of tarantula wait underground and spring upon their prey; there are also some that can actually lasso their prey with webs. Once they catch their preys, spiders use enzymes to liquefy the preys and drink them, since spider guts are too narrow to process solids.
All spiders have venom, but only a few are venomous enough to be dangerous to humans. In fact, many researches are being done on ways to utilize spider venom in medicine and pesticides. Spider silk is also being looked at, as it is light and strong. A strand of spider silk the thickness of a paper clip can support the weight of a grand piano. With that kind of strength, researchers are positive that spider silk could be used to build strong bullet-proof vests and other strength-requiring materials.
Unlike some other arthropods, it can often be difficult to differentiate between male and female spiders. The easiest method is to look for the genitalia on the mature spiders. In immature specimens, it is usually too difficult for evenexperts to differentiate the sexes. Male spiders usually have their genitalia attached to the end of their pedipalps. Although you may not recognize it at first, after some practice, you will be able to see the genitalia. Females, on the other hand, have their genitalia on the bottom of their abdomen, in close proximity of their head. The female genitalia looks a bit different amongst different species, but the best way to recognize the genitalia is to look at different specimens of the same species and see the differences between their abdomen.
Araneidae - Araneus - Araneus marmoreus (Orange Orb Spider):
Pisauridae - Pisaurina - Pisaurina mira (Nursery Web Spider):
