SPIDER ANATOMY

The cephalothorax is the first of 2 body parts on a spider.  It is a combination of the head and thorax, and on it are found the legs, eyes, pedipalps, chelicerae, and other mouthparts. The cephalothorax and abdomen are connected by a thin stalk called the "pedicel."  Among arachnids that live in Kentucky (including scorpions, daddy-long-legs, and mites) only spiders have this thin stalk between the abdomen and cephalothorax.  Some arachnids that do not live in Kentucky, such as Tailless Whipscorpions, also have a thin connection between the 2 body parts, and these creatures can be difficult to distinguish from spiders.

The chelicerae are a spider's jaws.  They are located on the very front of a spider's cephalothorax.  Every Kentucky spider has a pair of chelicerae, and they are tipped with fangs.  Chelicerae are filled with muscles, and are used to hold prey while the spider injects venom.  Note that a few rare spiders, such as those in the scientific family Uloboridae, do not have venom glands, although they possess fangs and chelicerae.

Spiders do not actually drink fluid through their fangs.  Located behind the chelicerae are other small mouthparts, including the labium and labrum. Along with the chelicerae, these mouthparts work together to direct food into the spider's mouth, which is hidden behind the chelicerae and other mouthparts.

Some spiders, like cobweb spiders, are only able to consume fluids, but most spiders are able to eat solid food after it has been shredded and mashed by the chelicerae.

In most spiders, the chelicerae are like scissors: they move from side to side.  But in some primitive spiders, such as bird spiders (a.k.a. tarantulas), trapdoor spiders, and purseweb spiders, the chelicerae move up and down, like 2 fingers side-by-side.  The Iziko Online Museum has an excellent diagram that illustrates these two types of chelicerae.

All of the other arachnid groups, including Scorpions, Mites, and Harvestmen, have chelicerae as well, but spiders are the only arachnids with venomous chelicerae.

Like the chelicerae, a spider's pedipalps are part of its mouth, and are located just between the chelicerae and first pair of legs on the cephalothorax. Pedipalps are jointed, and look somewhat like small legs. They are not used like legs, though.  Instead, they are more like antennae: pedipalps help the spider sense objects that it encounters.  Some spiders also use their pedipalps to shape their webs and to aid in prey capture and feeding.

All arachnids have pedipalps, but they often look quite different than spider pedipalps.  In Scorpions, for instance, the large pincers are actually modified pedipalps.

A spider's eyes are located on the cephalothorax.  Most spiders have 6 or 8 eyes.  Spider eyes are considered "simple": they do not have multiple lenses and facets as do the compound eyes found on some insects.  Although some spiders can only see the difference between light and shadow, others, especially Jumping Spiders, are believed to have excellent eyesight.

The spider's abdomen contains many important internal organs, such as the digestive tract, reproductive organs, and lungs.  Tipping the abdomen are the spinnerets.

A spider produces silk through tiny pores in its spinnerets.  Most spiders have 6 spinnerets.