Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about 3 millimetres long, are usually brown, and have bodies that are "flattened" sideways or narrow, enabling them to move through their hosts' fur or feathers. They lack wings; their hind legs are extremely well adapted for jumping. Their claws keep them from being dislodged, and their mouthparts are adapted for piercing skin and sucking blood. They can leap 50 times their body length, a feat second only to jumps made by another group of insects, the superfamily of froghoppers. Flea larvae are worm-like, with no limbs; they have chewing mouthparts and feed on organic debris left on their hosts' skin.
The Pterygota are a subclass of insects that includes all winged insects and the orders that are secondarily wingless.
Holometabola, also known as Endopterygota, is a superorder of insects within the infraclass Neoptera that go through distinctive larval, pupal, and adult stages. They undergo a radical metamorphosis, with the larval and adult stages differing considerably in their structure and behaviour. This is called holometabolism, or complete metamorphism.
The caddisflies, or order Trichoptera, are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the basis of the adult mouthparts. Integripalpian larvae construct a portable casing to protect themselves as they move around looking for food, while annulipalpian larvae make themselves a fixed retreat in which they remain, waiting for food to come to them. The affinities of the small third suborder Spicipalpia are unclear, and molecular analysis suggests it may not be monophyletic. Also called sedge-flies or rail-flies, the adults are small moth-like insects with two pairs of hairy membranous wings. They are closely related to the Lepidoptera which have scales on their wings; the two orders together form the superorder Amphiesmenoptera.
Mecoptera is an order of insects in the superorder Holometabola with about six hundred species in nine families worldwide. Mecopterans are sometimes called scorpionflies after their largest family, Panorpidae, in which the males have enlarged genitals raised over the body that look similar to the stingers of scorpions, and long beaklike rostra. The Bittacidae, or hangingflies, are another prominent family and are known for their elaborate mating rituals, in which females choose mates based on the quality of gift prey offered to them by the males. A smaller group is the snow scorpionflies, family Boreidae, adults of which are sometimes seen walking on snowfields. In contrast, the majority of species in the order inhabit moist environments in tropical locations.
The name Apterygota is sometimes applied to a former subclass of small, agile insects, distinguished from other insects by their lack of wings in the present and in their evolutionary history; notable examples are the silverfish, the firebrat, and the jumping bristletails. Their first known occurrence in the fossil record is during the Devonian period, 417–354 million years ago. The group Apterygota is not a clade; it is paraphyletic, and not recognized in modern classification schemes. As defined, the group contains two separate clades of wingless insects: Archaeognatha comprises jumping bristletails, while Zygentoma comprises silverfish and firebrats. The Zygentoma are in the clade Dicondylia with winged insects, a clade that includes all other insects, while Archaeognatha is sister to this lineage.
Apteropanorpidae is a family of wingless scorpionflies containing a single genus, Apteropanorpa, with four named species. These species, also called Tasmanian snow scorpionflies, are found in moss in Tasmania and southern Australia. The adults are generalised predators. The larvae live in moss and are locally common.
Nannochoristidae is a family of scorpionflies with many unusual traits. It is a tiny, relict family with a single extant genus, Nannochorista, with eight species occurring in New Zealand, southeastern Australia, Tasmania, Argentina and Chile. Due to the group's distinctiveness from other scorpionflies, it is sometimes placed in its own order, the Nannomecoptera. Some studies have placed them as the closest living relatives of fleas. Most mecopteran larvae are eruciform, or shaped like caterpillars. Nannochoristid larvae, however, are elateriform, and have elongated and slender bodies. The larvae are aquatic, which is unique among mecopterans. The larvae are predatory, hunting on the beds of shallow streams, primarily on the larvae of aquatic Diptera like chironomids.
The Empidoidea are a large monophyletic superfamily of true flies, the sister taxon to the Muscomorpha (Cyclorrhapha). These two groups are sometimes united in the unranked taxon Eremoneura. There are some 10,000 known species within Empidoidea, which are represented on all continents except Antarctica. They are known to have existed since the Jurassic period.
Amphiesmenoptera is an insect superorder, established by S. G. Kiriakoff, but often credited to Willi Hennig in his revision of insect taxonomy for two sister orders: Lepidoptera and Trichoptera (caddisflies). In 2017, a third fossil order was added to the group, the Tarachoptera.
Hypogastrura nivicola is a species of dark blue springtail. Its English name in the United States is snow flea, but there are also additional insects called by that name. They are often seen jumping about on the surface of snow on a warm winter's day in North America.
There are various disparate groups of wingless insects. Apterygota are a subclass of small, agile insects, distinguished from other insects by their lack of wings in the present and in their evolutionary history. They include Thysanura . Some species lacking wings are members of insect orders that generally do have wings. Some do not grow wings at all, having "lost" the possibility in the remote past. Some have reduced wings that are not useful for flying. Some develop wings but shed them after they are no longer useful. Other groups of insects may have castes with wings and castes without, such as ants. Ants have alate queens and males during the mating season and wingless workers, which allows for smaller workers and more populous colonies than comparable winged wasp species.
In the 10th edition of Systema Naturae of 1758–1759, Carl Linnaeus classified the arthropods, including insects, arachnids and crustaceans, among his class "Insecta". He described the Insecta as:
A very numerous and various class consisting of small animals, breathing through lateral spiracles, armed on all sides with a bony skin, or covered with hair; furnished with many feet, and moveable antennae, which project from the head, and are the probable instruments of sensation.
Panorpida or Mecopterida is a proposed superorder of Holometabola. The conjectured monophyly of the Panorpida is historically based on morphological evidence, namely the reduction or loss of the ovipositor and several internal characteristics, including a muscle connecting a pleuron and the first axillary sclerite at the base of the wing, various features of the larval maxilla and labium, and basal fusion of CuP and A1 veins in the hind wings. The monophyly of the Panorpida is supported by recent molecular data.
Boreus is the most diverse of three genera of insects in the family Boreidae. They are commonly known as winter scorpionflies due to their close relation to the true scorpionflies and preference for cold habitats.
Boreus brumalis, the mid-winter boreu, is a species of snow scorpionfly in the family Boreidae. It is found in North America.
Caurinus is a genus of snow scorpionflies in the family Boreidae. There are at least two described species in Caurinus.
Aneuretopsychidae is an extinct family of scorpionflies known from the Mesozoic. Fossils are known from the Jurassic (Callovian-Oxfordian) to the early Late Cretaceous (Cenomanian). It is part of Mesopsychoidea, a group of scorpionflies with siphonate proboscis. They are suggested to have been nectarivores, feeding off the liquid pollination drops of and acting as pollinators for now extinct insect pollinated gymnosperms such as Bennettitales.
Hymenopterida is a superorder of holometabolous (metamorphosing) insects. As originally circumscribed, it included Hymenoptera and the orders in Panorpida. However, more recent studies find Hympenoptera as sister to the other members of Holometabola and the superorder is restricted to Hymenoptera.
