The effect of psychological stress on masticatory muscle electromyography-a scoping review.

Several species of tarantulas are among the largest and longest-lived terrestrial invertebrates and are included in the family Theraphosidae. They are ubiquitous inhabitants of tropical and subtropical regions on most continents, with the exception of Antarctica. Species from the Americas and the Caribbean have developed an interesting defensive behavior of using urticating setae against potential predators and parasites, which has been recorded by naturalists since the 19th century. When a tarantula is disturbed, it usually flicks the abdomen dorsum with its hind legs, dislodging the setae, which are carried by the air and can contact the skin and eyes of the aggressor. They produce skin rashes and intense itching and may eventually cause damage to the human eyes. The morphology of some of these setae was first documented by Bertkau, but only studied in any detail almost a century later. Cooke et al. classified urticating setae into four types (I, II, III, IV) according to their morphology (Fig. A-D). Types I, III and IV are found on the abdomen dorsum of species now included in Theraphosinae, the largest Theraphosidae subfamily with 628 species and endemic to the Americas and the Caribbean. Urticating setae of types I and/or III are long, slender and have well-developed barbs (Figs. A, C). They are attached to the spider’s abdomen via a short stalk, and the penetrating tip lies at its distal portion. Type III setae (Fig. C) are typically the longest and most slender urticating setae, ranging from 0.3 to 1.8 mm in length. Type IV setae are very short (0.06 to 0.2 mm in length) (Fig. D), and their use is not well understood (but see Russi & Pérez-Miles. Type I ranges from 0.2 to 0.6 mm in size and is unique because of its morphology. There is an area of barbs directed toward its base, or the “main barbs”, followed by a region lacking well-developed barbs and then a region of “reversed barbs” close to its base(Fig. A). Type II setae (Fig. B) were considered to be exclusive to the genus ; however, more recently, this seta was found to be present in almost all 7 genera and 32 species of Aviculariinae, a subfamily composed of arboreal species distributed exclusively in the Americas and the Caribbean. Type II intrigued Cooke et al. due to its shape, which is thicker than those of the other types, almost entirelly covered with weakly developed barbs, and the position of the penetrating tip is in a basal position (Fig. B). A few decades later, these setae were shown to be used in direct contact with potential predators when the spider rubs the abdomen dorsum against the aggressor. Type V was described by Marshall & Uetz and is exclusive to the genus , with five species distributed in northern South America and belonging to the small subfamily Psalmopoeinae. Interestingly, the urticating setae are located in the distal prolateral area of the femur palp and are released by movements of the palps against the chelicerae (see 1 and 2 in Marshall & Uetz. Two other morphological types have been described as types VI and VII for the theraphosine genera (see 4 in Pérez-Miles and (see fig. 2 in Perafán et al.) from Mexico and Colombia, respectively. Type VI is inserted directly into the stalks with penetrating tips and type VII morphologically resembles type II, but the penetrating tip is distal. Table  summarizes information about the types of urticating setae.