[1] The forewings are modified into small club-shaped structures called halteres, which sense gyroscopic information.

[1][9][7] Adult female mengenillids are wingless but are free living and somewhat mobile with legs and small eyes.

[10][9][7] Newly hatched primary (first instar) larvae are on average 230 micrometres (1⁄128 in) in length, smaller than many single-celled organisms.

The underside of the body is covered in minute hair-like structures (microtrichia), which allow the larvae to stick to wet surfaces via capillary action.

In all strepsipterans the male mates by rupturing the female's cuticle (in the case of Stylopidia, this is in a deep narrow fissure of the cephalothorax near the birth canal).

Sperm passes through the opening directly into the body in a process called traumatic insemination, which has independently evolved in some other insects like bed bugs.

[citation needed] Larvae of Stichotrema dallatorreanum Hofeneder from Papua New Guinea were found to enter their orthopteran host's tarsus (foot).

[1] Strepsiptera of various species have been documented to attack hosts in many orders, including members of the orders Zygentoma (silverfish and allies), Orthoptera (grasshoppers, crickets), Blattodea (cockroaches), Mantodea (praying mantis), Heteroptera (bugs), Hymenoptera (wasps, ants and bees), and Diptera (flies).

Strepsiptera were once believed to be the sister group to the beetle families Meloidae and Ripiphoridae, which have similar parasitic development and forewing reduction.

Early molecular research suggested their inclusion as a sister group to the flies,[1] in a clade called Halteria,[22] which have one pair of the wings modified into halteres,[23] and failed to support their relationship to the beetles.

[23] Further molecular studies, however, suggested they are outside the clade Mecopterida (containing the Diptera and Lepidoptera), but found no strong evidence for affinity with any other extant group.

[24] Study of their evolutionary position has been problematic due to difficulties in phylogenetic analysis arising from long branch attraction.

[28] The earliest known strepsipteran fossils are those of Cretostylops engeli (Cretostylopdiae) and Kinzelbachilla ellenbergeri, Phthanoxenos nervosus and Heterobathmilla kakopoios (Phthanoxenidae), discovered in middle Cretaceous Burmese amber from Myanmar, around 99 million years old, which all lie outside the crown group, but are all more closely related to modern strepsiperans than Protoxenos is.

[18]The vast majority of living strepispterans are placed within the grouping Stylopidia, which includes the families Corioxenidae, Halictophagidae, Callipharixenidae, Bohartillidae, Elenchidae, Myrmecolacidae, Stylopidae, Protelencholacidae (extinct) and Xenidae.

[13] Strepsipteran insects in the genus Xenos parasitize Polistes carnifex, a species of social wasps.

Here they remain until they thrust through the cuticle and pupate (males) or release infective first-instar larvae onto flowers (females).

[30] After:[2] †Protoxenidae †Cretostylopidae †Phthanoxenidae †Mengeidae Bahiaxenidae Mengenillidae Corioxenidae Bohartillidae Halictophagidae Elenchidae †Protelencholacidae Myrmecolacidae Callipharixenidae Xenidae Stylopidae Some insects which have been considered pests may have strepsipteran endoparasites.