The old Thysanura or three pronged bristle-tails, are an obsolete order linking the Apterygota (primarily wingless insects) and the Pterygota (primarily winged insects), and contain some of the most primitive of insects known to man i.e., the Thysanura are most like what we think the first insects looked like. The Protura, Diplura and Collembola representing other branches from a shared arthropodal ancestor, which along with the Archeognatha ( here part of the Thysanura) are considered part of the 'Hexapoda' but not part of the 'Insecta' the Hexapoda is a separate class of arthropods including the smaller group the 'Insecta' which contains the rest of what we think of as 'The Insects' in classification schemes (see The Tree of Life).
Flightless insects with ectognathous mouth parts (externally visible as compared to entognathous mouth parts of the Diplura, Protura and Collembola which are sunk into the head and thus not immediately visible). They have long filiform antennae with as many as, or more than 30 segments. The abdomen has eleven segments generally ending in three 'tails' consisting of two cerci and a telson. They are commonly represented by the Silverfish and the Firebrats often found in houses and bakeries respectively.
They spend most of their life concealed beneath or within stones, wood, houses, the soil etc., and they mostly feed on dead plant material and fungal hyphae. There are more than 820 species in the world some of which now have a global distribution. Nine species have been found in the British Isles and 30 in Europe as a whole.
Fertilization is indirect, meaning the males leave packets of sperm, called spermatophores, attached to the substrate for the females to find, therefore there is no contact between the sexes for mating and no courtship.
They lay their eggs (normally between 5 and 20) in small crevices or loose in the substrate, although some members of the family Nicoletiidae lay their eggs singly, one here, one there. Their eggs are colored orange, brown or grey when laid but quickly darken. The young possess an egg tooth in their first instar, this helps them escape the egg. They look like miniature (but pale adults). They do not gain the scales that give them their color until the 2nd instar in the Microcoryphia and the 3rd instar in the Zygentoma.
The time taken to reach maturity varies considerably, in some species they become sexually active after the 9th instar, but in others not until the 14th or 15th. They live relatively long lives, up to 4 years, and continue to moult regularly as adults.
Their most common natural enemies are spiders, although centipedes and carabid beetles are also know to eat them. Internally they may be parasitized by Sporozoans and externally they can have a problem with erythraeid mites. Some species of Zygentoma are also parasitized by Strepsipterans.
Some members of the Zygentoma, such as the SilverFishes (Lepisma saccharina & Ctenolepisma longicauda) and the Firebrat (Lepismodes inquilinus) can be a nuisance in homes and offices where they will eat both paper and cotton. They possess their own cellulase enzymes and are not dependant on bacteria to digest such products, in the way Termites are for instance.
There are a three lovely paintings of some thysanura done by A.T.Hollick in the 1860's in John Lubbock's 1871 monograph on the Collembola and Thysanura,
Machilis maritima36k jpg
Lepisma saccharina 37k jpg
Machilis polypoda 30k jpg
The Thysanura are now divided into two separate Orders.
1) The Microcoryphia (equivalent to the old Machiloidea) with only one mandibular articulation (sometimes known as the Archeognatha) which contains two families. The Microcoryphia can be recognised by the fact that their Maxillary palps are long and they generally hold them out in front of their body in between their antennae. The Microcoryphia can also be recognised by the fact that they have large compound eyes that meet together on the top of the head and 3 ocelli. Also they can jump (using their abdomen). Their lateral cerci are shorter than the central telson. About 460 species worldwide.
2) The Zygentoma (equivalent to the old Lepismatoidea) with two mandibular articulations (note that the Pterypgote insects all possess two mandibular articulations) which contains three families. The Zygentoma can be distinguished from the Microcoryphia by their small, or absent eyes and the fact that they often hold their two lateral cerci out at right-angles to the body, their lateral cerci are often as long as the central telson. They can have from 1 to 3 ocelli. Also they generally hold their Maxillary palps to the outside of their antennae. They cannot jump. About 380 species worldwide.