Urticating hair. Scanning electron micrographs (SEM) of the urticating hair of the Mexican Red Knee Tarantula (Brachypelma smithi). Some of the “new world” tarantulas have two major defence systems, the obvious being venom but also they have special hairs on their opisthosoma or abdomen known as urticating hairs. When in fear of attack, they will rub their hind legs against their abdomen flicking the hairs at the enemy. The tiny hairs or bristles get into the skin and mucous membranes of the attacker and can cause much irritation and even edema which is sometimes fatal. Studies on these special bristles indicate that they cause both mechanical and chemical harm to the membranes and skin. After kicking off the hairs, the tarantula will have a bald patch on its abdomen. The hairs will not grow back but will be replaced when the spider next moults. Magnification x2910 (x720 at 10cm wide).
