What are Spiders
There are approximately 38,000 known species of spiders. There are probably as many more to be discovered. Spiders are vital to a healthy ecosystem. They eat harmful insects and pollinate plants. They are also a valuable food source for many small mammals and birds. Spiders eat more insects than birds and bats combined. All spiders spin silk, but not all spiders spin webs. When a spider travels, it always has four legs touching the ground and four legs off the ground at any given moment.
Spiders have blue blood. In humans, oxygen is bound to hemoglobin, a molecule that contains iron and gives blood its red color. In spiders, oxygen is bound to hemocyanin, a molecule that contains copper rather than iron. A spider’s muscles pull its legs inward, but cannot extend its legs out again. Instead, it must pump a watery liquid into its legs to push them out. A dead spider’s legs are curled up because there is no fluid to extend the legs again. Spiders have between two and six spinnerets at the back of their abdomen. Each one is like a tiny showerhead that has hundreds of holes, all producing liquid silk.