Male spiders are unique among all animals in having a secondary copulatory organ. While most animals spread their sperm in water or insert them into the female, mature male spiders weave a small "sperm" web. They place a drop of semen on the web, suck it up with their pedipalps (special structures on their first "arm"), and then use the pedipalp to insert the sperm into a female.
Some spiders live underwater all of their lives. They surface to collect a bubble of air, which acts as an underwater lung. An underwater spider fills its bell-shape web with air bubbles and derives oxygen from them.
The fisher or raft spider is able to walk across the surface of a pond or other body of water by skating like a water strider. When it detects prey (insects or tiny fish) under the surface, it can quickly dive to capture its dinner.
Hummingbirds use the silk from spider webs to weave together the sticks that form their nests.
A few species of trapdoor spiders use their abdomens to "plug" their burrows to protect themselves from wasps. The abdomen is flat on the back end and tough enough that a wasp's stinger can't penetrate it.
Spiders eat more insects than birds and bats (combined) eat, so they should be considered another of human's best friends. They play a big role in controlling insect populations.
The decoration in the web of some orb-weaving spiders serves a variety of purposes: It can be a warning so birds don't fly into the web, an attractant so insect-prey fly in on purpose, or an "um-brella" to shade the spider from the hot sun.
Some orb weavers make very unusual webs. One variety greatly increases the area above the center, creating what is sometimes called a ladder web that extends eight feet above the spider.
Bolas spiders make webs of a single line with a sticky "ball," or bola, on the end. These spiders can twirl the bolas in the air. Moths are attracted to the smell and fly toward the web until they hit it and stick. The spider then reels in its catch.
This article was adapted from "The Book of Incredible Information," published by West Side Publishing, a division of Publications International, Ltd.