Embioptera

The order Embioptera, commonly known as webspinners, are a small group of mostly tropical and subtropical insects, classified under the subclass Pterygota. The order has also been referred to as Embiodea or Embiidina. The name Embioptera ('lively wings') comes from Greek, εμβιος, embios meaning 'lively' and πτερον, pteron meaning 'wing', a name that has not been considered to be particularly descriptive for this group of fliers, perhaps instead referring to their remarkable speed of movement both forward and backward. The group probably first appeared during the Jurassic and is well represented in Cretaceous amber. The common name webspinner comes from the insects' unique ability to spin silk from structures on their front legs. They use the silk to make a web-like pouch or gallery in which they live. Over 360 embiopteran species have been described, along with estimates of around 2000 species being in existence today. There is some debate as to the exact phylogenetic classification of Embioptera, with the order having been classed as a sister group to both orders Zoraptera, and Phasmatodea, and there is continuing dispute today concerning the accuracy of these classifications. The order is distributed all over the world, being found on every continent except Antarctica, with the highest density and diversity of species being located in tropical regions. All webspinners have a remarkably similar body form, although they do vary in colouration and size. The majority are brown or black in colour, ranging through to a pink or reddish shades in some species, and range in size from 15 to 20 mm (0.6 to 0.8 in). The body form of these insects is completely specialised for the silk tunnels and chambers in which they reside, being long, narrow and highly flexible. All the females and nymphs are wingless, whereas adult males can be either winged or wingless depending on species. The head has projecting mouthparts with chewing mandibles. The compound eyes are kidney-shaped, there are no ocelli, and the antennae are long, with up to 32 segments. The body is cylindrical in form, adapted for the tubular galleries within which the insects live. The first segment of the thorax is small and narrow, while the second and third are larger and broader, especially in the males, where they include the flight muscles. The wings, where present, occur as 2 pairs that are similar in size and shape: long and narrow, with relatively simple venation. These wings operate using basic hydraulics; pre-flight, chambers within the wings fill with hemolymph, making them rigid enough for use. On landing these chambers empty and wings become flexible, folding back against the body. Wings can also fold forwards over the body, and this, along with the flexibility allows easy movement through the narrow silk galleries without resulting in damage. In both males and females the legs are short and sturdy, with an enlarged tarsomere on the first pair, containing the silk-producing glands. The abdomen has ten segments, with a pair of cerci on the final segment. These cerci are highly sensitive to touch, and allow the animal to navigate while moving backwards through the gallery tunnels, which are too narrow to allow the insect to turn round. Because morphology is so similar between species, it makes species identification extremely difficult. For this reason, the main form of taxonomic identification used in the past has been close observation of distinctive copulatory structures of males, (although this method is now thought by some entomologists and taxonomists as giving insufficient classification detail). Although males never eat during their adult stage, they do have mouthparts similar to the females. These mouthparts are used to hold onto the female during copulation. After molting and mating, the female lays a single batch of eggs either within the existing gallery, or will find new territory to start a new colony. Here, the eggs hatch into nymphs that resemble small, wingless adults (images right and below). After a short period of parental care, the nymphs undergo hemimetabolosis (moulting into several instars before emerging as a fully grown adult after the last moult), molting a total of four times before reaching adult form. Adult males never eat, and leave the home colony almost immediately to find a female and mate. Those males that can not fly will often mate with females in nearby colonies, meaning their chosen mates are often siblings or closely related. In some species, the female will eat the male after mating, but in any event, the male will not survive for long after mating. A few species are known to be parthenogenetic, meaning they are able to produce viable offspring without fertilisation of eggs. This phenomenon occurs when a female is, for whatever reason, unable to find a male to mate with, thus giving her and her species reproductive security at all times.