This is an order of insects nobody notices. Even scientifically little is known about these creatures. They are all small insects, fully adapted to living the life of a parasite inside another insect. After hatching the larvae have legs and are quite mobile. Immediately they search for a host. Once they find one they use an oral secretion to soften the chitine of the host and crawl inside. Once in the larva moults at once and turns into a maggot like creature without eyes or legs and with a very rudimentary mouth. It lives by filtering particals out of the blood of the host. Even oxygen is taken from the host's blood. Their skin is adapted for both these tasks, so the mouth is not used anymore. The females keep on looking like a maggot, even when adult. They develop no wings, antennae, eyes, legs or even external sexual organs. After having moulded for the last time, they just stick their heads out of the host's body between two segments. They are now waiting for a male to mate. The males however moult into real insect-looking creatures: they have a mouth, legs, antennae, strawberry like eyes and one pair of wings. The other pair is reduced to halter like organs, just as in flies. The difference is that in flies it is the second pair of wings that is reduced, in twisted-wing parasites it is the first pair. The males live for a couple of hours only and die right after mating. The females produce a great number of offspring, wich probably indicates most larvae won't find a host in time.
At this moment there are some 600 species known to man, of which only 17 live in Britain. Because they are extremely hard to find, it is possible there are many more species, probably even in Britain. In Europe most species are parasites to wasps and bees. A few species are known to attack bugs. Most species are so inconspicuous you'll never see them at all. Only one species, Stylops melittae, is sometimes seen, when the adult females stick their head out of the host, unvariably a bee. A bee infected with a parasite is called a stylopised bee. Such a bee sometimes behaves oddly and it is claimed he or she is infertile. The picture in the middle proves that a stylopised bee is still capable of mating. You can see the head of the parasite sticking out between two segments of the female bee just in front of the males front leg. In this case the victim is the Buffish Mining-bee (Andrena nigroaenea). Mining bees are regularly found to be stylopised.