their hind legs against the opisthosoma throwing the urticating hairs in the direction of the enemy. The cloud of small bristles will get into the mucous membrane of small mammals and cause edema, which can be fatal. The bristles cause both mechanical and chemical harm to the skin and membranes. Reaction and the degree of irritation to a defensive urticating hair barrage can vary tremendously, based on the species in question. Some, such as those of the Chilean rose tarantula (Grammastola rosea) and the pinktoe tarantula (Avicularia avicularia), are fairly mild and innocuous to humans. Others, such as those of the Brazilian giant white knee tarantula (Acanthoscurria geniculata), are moderately irritating. Still others, such as the Goliath birdeater (Theraphosa blondi), are far more severe. These bristles can result in painful rashes, and have been likened to sharp shards of fiberglass. After kicking urticating hairs, the tarantula will have a bald spot on its abdominal region. As territorial markings Urticating hairs are not just thrown at an enemy as a first line defense, but are also used as an indication of territory. They can be found on and around the burrow entrance and in webbing for protection (for example, some subfamily Theraphosinae species include these bristles in cocoon silk). Urticating hairs protect tarantula egg sacs (Avicularia spp. and Theraphosa blondi respectively). This is thought to discourage fly larvae from consuming their eggs and young. Human reactions In humans, urticating hairs can cause allergic skin reactions which can manifest as inflammation, rash and itching. The reactions can last from several hours to weeks. Ophthalmia nodosa, an irritation reaction, can result when the barbed bristles lodge in the cornea. Handlers are advised to wear eye protection. Notes References External links Urticating Caterpillars chapter in United States Environmental Protection Agency and University of Florida/Institute of Food and Agricultural Sciences National Public Health Pesticide Applicator Training Manual Summary of Lancet article at Physorg. Animal hair Antipredator adaptations Plant physiology Spider anatomy