This is a urticating bristle from my pet tarantula. These bristles are the hair-like structures found on the spider's body. When the spider is disturbed, it uses its back legs to pull out some of the bristles and throw them into the air. If you look at the photo, you can see that the bristle is covered with tiny spines. The spines embed themselves into the eyes, nose, mouth, and skin of a predator, causing an intense itching, burning sensation. Luckily, the bristles of my spider, a Brazilian Salmon Pink Bird-Eating Tarantula (Lasiodora parahybana) are not extremely irritating. Some of the other tarantulas I have worked with are MUCH worse. Some have been known to kill mice by kicking up a cloud of bristles, which the mouse inhales. This causes irritation and swelling, which can suffocate the mouse.

Way back when I was a kid, you could buy itching powder from ads in the back of comic books. You would put it down someone's back to cause intense itching. That itching powder was actually urticating bristles from tarantulas.