There are over 35,000 spider species, the largest of them being the tarantula. Spiders can be found everywhere and they have been roaming the earth for over 300 million years. There are two main groups of spiders. The first being the trappers, or web builders that wait in webs to snare other insects. The hunters and ambushers seek out their prey on plants or on the ground, capturing insects with their powerful legs and chelicerae. Spiders are invertebrates with jointed legs and a protective external exoskeleton. They differ from insects in that they have two major body segments, four pairs of legs and a pair of chelicerae instead of mandibles. They are also capable of producing silk from glands located in the abdomen. They use the silk for building webs to capture their prey, lining burrows, aerial ballooning activities and wrapping eggs. Spiders do not harm plants, but rid them of harmful arthropods. Their venom is used to paralyse their pray and begin the digestion process. With the exception of a few they are virtually harmless to man.