Beetles are insects that form the order Coleoptera, in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 described species, is the largest of all orders, constituting almost 40% of described insects and 25% of all known animal species; new species are discovered frequently, with estimates suggesting that there are between 0.9 and 2.1 million total species. However, the number of beetle species is challenged by the number of species in dipterans (flies) and hymenopterans (wasps).
Spercheus is a genus of aquatic beetles which are placed in a family of their own, Spercheidae within the Hydrophiloidea. About 20 species are known from around the world except the Nearctic with the majority being from the Oriental and Afrotropical Realms.
The whirligig beetles are water beetles, comprising the family Gyrinidae that usually swim on the surface of the water if undisturbed, though they swim underwater when threatened. They get their common name from their habit of swimming rapidly in circles when alarmed, and are also notable for their divided eyes which are believed to enable them to see both above and below water. The family includes some 700 extant species worldwide, in 15 genera, plus a few fossil species. Most species are very similar in general appearance, though they vary in size from perhaps 3 mm to 18 mm in length. They tend to be flattened and rounded in cross section, in plain view as seen from above, and in longitudinal section. In fact their shape is a good first approximation to an ellipsoid, with legs and other appendages fitting closely into a streamlined surface. Whirligig beetles belong to the beetle suborder Adephaga, which also includes ground beetles and diving beetles.
The Hydroscaphidae are a small family of water beetles known commonly as skiff beetles. As of 2010, there are 23 species in the family. Several are recently described.
The Haliplidae are a family of water beetles that swim using an alternating motion of the legs. They are therefore clumsy in water, and prefer to get around by crawling. The family consists of about 200 species in 5 genera, distributed wherever there is freshwater habitat; it is the only extant member of superfamily Haliploidea. They are also known as crawling water beetles or haliplids.
The Adephaga are a suborder of beetles, and with more than 40,000 recorded species in 10 families, the second-largest of the four beetle suborders. Members of this suborder are collectively known as adephagans. The largest family is Carabidae which comprises most of the suborder with over 40,000 species. Adephaga also includes a variety of aquatic beetles, such as predaceous diving beetles and whirligig beetles.
The Dytiscidae – based on the Greek dytikos (δυτικός), "able to dive" – are the predaceous diving beetles, a family of water beetles. They occur in virtually any freshwater habitat around the world, but a few species live among leaf litter. The adults of most are between 1 and 2.5 cm (0.4–1.0 in) long, though much variation is seen between species. The European Dytiscus latissimus and Brazilian Megadytes ducalis are the largest, reaching up to 4.5 and 4.75 cm respectively. In contrast, the smallest is likely the Australian Limbodessus atypicali of subterranean waters, which only is about 0.9 mm (0.035 in) long. Most are dark brown, blackish, or dark olive in color with golden highlights in some subfamilies. The larvae are commonly known as water tigers due to their voracious appetite. They have short, but sharp mandibles and immediately upon biting, they deliver digestive enzymes into prey to suck their liquefied remains. The family includes more than 4,000 described species in numerous genera.
Helophorus is the only genus in the beetle family Helophoridae within the Hydrophiloidea. They are small insects, found mainly in the Holarctic region, but two or three species also live in the Afrotropical region, Central America and one in the Indomalayan region.
Hygrobia is a genus of aquatic beetles native to Europe, North Africa, China and Australia. It is the only genus in the family Hygrobiidae, also known as the Paelobiidae. These are known commonly as squeak beetles or screech-beetles.
Acilius sulcatus is a species of water beetle in the family Dytiscidae. It is fairly large, with color variation shown throughout its range. Typically it is yellow and black.
Amphizoa lecontei is a species of aquatic beetle. Adults have a body length of between 11.5 and 16 millimeters. Its elytron has a distinct carina on fifth interval. The species is found in western North America, especially in the Rocky Mountains. Its common name is "Trout-stream beetle". Its synonym is Amphizoa carinata.
Amphizoa insolens is a species of aquatic beetles. It is found in North America from Alaska to southern California.
Aspidytes is a genus of aquatic beetles in the family Aspidytidae, first recorded in 2002 from specimens in South Africa. The genus contains the single species Aspidytes niobe. Originally a second species from China was placed in the same genus but has later been transferred to Sinaspidytes. The aquatic beetle is 6.5 - 7.2 mm long and lives in hygropetric habitats.
Hydroporini is a tribe of predaceous diving beetles in the family Dytiscidae. There are at least 730 described species in Hydroporini.
Bidessini is a tribe of predaceous diving beetles in the family Dytiscidae. There are at least 40 genera and at least 630 described species in Bidessini.
Oreodytes scitulus is a species of predaceous diving beetle in the family Dytiscidae. It is found in North America.
Dytiscinae is a subfamily of predaceous diving beetles in the family Dytiscidae. There are at least 20 genera and 380 described species in Dytiscinae.
Eretes sticticus, the western erete, is a species of predaceous diving beetle in the family Dytiscidae. It is found in Africa, the Middle East, and the Americas from the southern United States to Peru. This species preys specifically on mosquito larvae in ponds and pools. They can kill up to all the instar larvae of the mosquito depending on size and density of the prey.
Aspidytidae is a family of aquatic beetles of the suborder Adephaga, described in 2002 from specimens in South Africa and China. There are only two known species in the family and these were originally described in the genus Aspidytes, but later the new genus Sinaspidytes was erected for the species found in China. The family can also be referred to by its trivial name cliff water beetles.
Sinaspidytes is a genus of aquatic beetles in Aspidytidae, first recorded in 2003 from specimens in the Shaanxi province, China. It is monotypic, with the only species being Sinaspidytes wrasei. Originally this species was placed in the genus Aspidytes with a second species from South Africa, but was later transferred to Sinaspidytes. The genus contains the single species S. wrasei. The aquatic beetle is 4.8 - 5.2 mm long and lives in hygropetric habitats.
