Some spiders lie in ambush and snatch any insect that comes too close.
Other spiders hunt for the insects and other arthropods that they eat, then pounce on them as a cat pounces on a mouse.
But most spiders, which happen to be those that are most familiar to people, trap their prey in silken webs.
All spiders are venomous and use the venom to subdue their prey.
The venom is injected by a pair of fangs that grasp and pierce the prey animal.
Each fang is traversed by a duct, a narrow tunnel, that carries the venom from a poison gland near its base to an opening at the tip of the fang.
Many spiders first inject the intact body of the prey with digestive enzymes that liquefy its tissues.
This liquid is then sucked up, and the spider discards the more or less intact outer shell of the prey.
Other spiders crunch up the prey to expose its soft inner tissues and then flood them with digestive enzymes.
After sucking up their meal, they discard a shapeless mass of chewed-up outer shell.
All spiders are predators that eat other animals, usually insects but also other arthropods.
A few of the larger spiders eat small vertebrates, including birds.
About 2,500 out of a total of about 30,000 known species in the world can be found in North America.
But many spiders, probably including quite a few North American species, have yet to be discovered and named.
Most people know what spiders look like and most spiders are easily recognized, among the exceptions are some small spiders that are very deceptive mimics of ants.
Speaking more technically, spiders are arachnids that have an unsegmented abdomen that is attached to the cephalothorax by a slender stem.
You may have to look closely to see this stem.
Arachna, a Greek word that means spider, also appears in the context of Greek mythology.
As the myth tells us, Arachne of Lydia was a Greek woman who became such a skilled weaver that she ventured to challenge the goddess Athena, who was also a great weaver, to a contest.
The goddess wove a tapestry that portrayed the gods as majestic beings.
Arachne wove an even more beautiful tapestry that showed the gods enjoying their amorous adventures.
Enraged at the perfection her rival’s creation, Athena tore it to pieces.
Arachne hanged herself in despair.
But the goddess took pity on her and turned the rope into a cobweb and Arachne into a spider.
An arachnid is, not surprisingly, a member of the class Arachnida, which consists of many sorts of creatures that are quite different from each other, including, among others, spiders, scorpions, harvestmen (daddy long legs), mites, and ticks.
The segments of an arachnid’s body are grouped as two regions, the cephalothorax, a combination of head (cephalon) and thorax, and an abdomen that bears no appendages.
The cephalothorax has four pairs of walking legs plus one more pair of legs, called the pedipalps, that are near the mouth and have been greatly modified to serve as antennae, or feelers.
Millipedes don’t attack people and are not dangerous.
But if a millipede is handled, the defensive fluid that oozes from its body may irritate the skin.
Some species curl themselves up into tight balls, thus exposing only their armored upper sides to the predator.
Many millipedes, but not all of them, have a series of stink glands that open along the sides of the body and that, if the millipede is attacked, emit a fluid or a vapor with an offensive smell.
In at least some species, this fluid contains hydrogen cyanide and is sometimes strong enough to kill insects that are confined in a closed jar with an individual of one of these species.
