Thysanura is an order of insects, encompassing silverfish and firebrats, best known for their three long caudal filaments. The name Thysanura is derived from the Greek θυσάνος, thysanos for fringe, tassel, bristle and ουρα, oura for tail, a reference to the three fanned out caudal filaments.
The families Machilidae and Meinertellidae of the jumping bristletails were once included with Thysanura. Occasionally, the correspondingly restricted order Thysanura is referred to as Zygentoma.
Silverfish are so called due to the silvery glitter of the scales covering their bodies. Their movement is "fish-like" and makes it look as if they are swimming. They are less than 1 centimetre (0.39 in) long, and found in damp corners or amongst books and paper in houses.
Order Zygentoma is also known as Order Thysanura. They are distributed worldwide. About 320 species have been described. The common names for the species are silverfish and firebrats. They get their name from the silver scales on some of the species. Their distinguishing characteristic is their three caudal filaments. They do not have wings. Silverfish are about two to twenty millimeters in length. They can either be found indoors amongst books or outdoors under stones, bark, or fungi. Outdoor silverfish feed on plant materials and indoor silverfish feed on wallpaper glue or book binding paste. Young silverfish will usually molt between twenty to seventy times. The molts only make them larger in size. They live for about one to four years. They can be found in the fossil record as far back as the Late Carboniferous.
Silverfish have flattened bodies and may be elongated or oval in shape. They have flexible antennae and small or absent compound eyes. They have short mandibles and relatively unspecialised mouthparts. Many species also have a number of short appendages on their abdominal segments, but the most distinctive feature of the group is the presence of three long, tail-like filaments extending from their last segment. The two lateral filaments are formed from the abdominal cerci (Hoell et al. 1998).
Silverfish may be found in moist, humid environments or dry conditions, both as free-living organisms or nest-associates. They feed on cereals, paste, paper, starch in clothes, rayon fabrics and dried meats. Silverfish can sometimes be found in bathtubs or sinks at night, as they have difficulty moving on smooth surfaces and so become trapped. Wild species often are found in habitats such as caves, and some are commensals living in association with ant colonies, e.g., Trichatelura manni (Torgerson & Akre 1969). There are no current species formally considered to be at conservation risk, though several are troglobites limited to one or a few caves or cave systems, and these species run an exceptionally high risk of extinction.
Life History and Behavior
Silverfish continue to moult throughout their life, with several sexually mature instars, unlike the pterygote insects. They are relatively slow growing, and lifespans of up to four years have been recorded (Hoell et al. 1998).
Silverfish have an elaborate courtship ritual to ensure exchange of sperm. The male spins a silken thread between the substrate and a vertical object. He deposits a sperm packet (spermatophore) beneath this thread and then coaxes a female to walk under the thread. When her cerci contact the silk thread, she picks up the spermatophore with her genital opening. Sperm are released into her reproductive system, and then she ejects the empty spermatophore and eats it.
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