Қышқылдандыратын түктер мен қылшықтар

Bristles on plants and animals that cause physical irritation when embedded

Urticating hairs or urticating bristles are one of the primary defense mechanisms used by numerous plants, almost all New World tarantulas, and various lepidopteran caterpillars. Urtica is Latin for "nettle" (stinging nettles are in the genus Urtica), and bristles that urticate are characteristic of this type of plant, and many other plants in several families. This term also refers to certain types of barbed bristles that cover the dorsal and posterior surface of a tarantula's or caterpillar's abdomen. Many tarantula species eject bristles from their abdomens, directing them toward potential attackers. These bristles can embed themselves in the other animal's skin or eyes, causing physical irritation, usually to great discomfort. The term "hairs" is technically a misnomer, as only mammals possess true hairs. The scientific term for plant hairs is trichomes.

The most common form of urticating hairs in plants are typified by nettles, which possess sharp pointed hollow bristles seated on a gland that secretes an acrid fluid. The points of these bristles usually break off in the wound, and the acrid fluid is pressed into it. Various plants unrelated to true nettles (Urtica species) possess similar defensive bristles, and the common names often reflect this (e. g. "bull nettle"). Many cacti of the sub family Opuntioideae feature fine, loosely attached short spines called glochids. When the plant is disturbed many of these spines fall off and penetrate the skin, causing irritation. Many glochidia are barbed, complicating their removal and enhancing their persistence in the skin. Exposure to glochidia is an occupational hazard to fruit pickers and other outside workers in areas where Opuntioideae thrive, as the spines can persist in clothing and gloves and can become airborne under the right conditions.

Not all urticating hair types are exhibited by each species of tarantula. Type II urticating hairs can be found in the genera Avicularia, Iridopelma and Pachistopelma (subfamily Aviculariinae). Type I and III urticating hairs are representative on a wide diversity of large bodied genera in the subfamily Theraphosinae Lasiodora and Acanthoscurria Nhandu spp., Megaphobema spp., Sericopelma spp., Eupalaestrus spp., Proshapalopus spp., Brachypelma spp., Cyrtopholis spp., and others, although some only have Type I in mature males. Unusually, Type III urticating hair is found alone on the species of Theraphosa spp., but these otherwise are similar to many species that also have Type I hairs. Type III alone is found in many 'dwarf' new world genera Hapalopus spp Type IV is found in several South American genera Grammostola, Euathlus etc. (exhibits types III and IV). Type V urticating hair is typical of the species of genus Ephebopus. They are located on the pedipalps. They are much shorter and lighter in contrast with other types of urticating hair. These are easily thrown by the spider into the air. Type VI urticating hair is found in the genus Hemirrhagus. Genera with the most urticating hairs are Lasiodora, Grammostola and Acanthoscurria.

New World tarantulas will, at the moment of danger, turn toward the attacker and briskly rub their hind legs against the opisthosoma throwing the urticating hairs in the direction of the enemy. The cloud of small bristles can 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.

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.

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.