Aquatic insects

Plecoptera is an order of insects, commonly known as stoneflies. Some 3,500 species are described worldwide, with new species still being discovered. Stoneflies are found worldwide, except Antarctica. Stoneflies are believed to be one of the most primitive groups of Neoptera, with close relatives identified from the Carboniferous and Lower Permian geological periods, while true stoneflies are known from fossils only a bit younger. Their modern diversity, however, apparently is of Mesozoic origin.

The caddisflies (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 (moths and butterflies) which have scales on their wings; the two orders together form the superorder Amphiesmenoptera.

Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the order Ephemeroptera. This order is part of an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies. Over 3,000 species of mayfly are known worldwide, grouped into over 400 genera in 42 families.

Mosquitoes, the Culicidae, are a family of small flies consisting of 3,600 species. The word mosquito (formed by mosca and diminutive -ito) is Spanish and Portuguese for little fly. Mosquitoes have a slender segmented body, one pair of wings, three pairs of long hair-like legs, and specialized, highly elongated, piercing-sucking mouthparts. All mosquitoes drink nectar from flowers; females of some species have in addition adapted to drink blood. The group diversified during the Cretaceous period. Evolutionary biologists view mosquitoes as micropredators, small animals that parasitise larger ones by drinking their blood without immediately killing them. Medical parasitologists view mosquitoes instead as vectors of disease, carrying protozoan parasites or bacterial or viral pathogens from one host to another.

Aquatica lateralis, known as "heike-botaru" (ヘイケボタル) in Japanese, is a species of firefly found in Russia, Japan and Korea. It was formerly placed in the genus Luciola. The larvae are aquatic and live in rice paddies.

Eusthenia spectabilis is a very large species of stonefly in the family of giant stoneflies, Eustheniidae. At 4 cm (1.6 in) Eusthenia spectabilis is the largest member of the genus and emerges later than other similar species.

Nipponoluciola cruciata, known as "genji-botaru" (ゲンジボタル) in Japanese, is a species of firefly found in Japan. Its habitat is small ditches and streams, and its larvae are aquatic. It was formerly known as Luciola cruciata but was revised taxonomically in 2022.

Thaumatoperla flaveola is a species of stonefly in the genus Thaumatoperla. They are endemic to the Mount Buller–Mount Stirling area of the Victoria alps, Australia.

The Dytiscidae, from the Ancient Greek word δυτικός (dystikos), meaning "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 in terrestrial habitats such as among leaf litter. The “diving” in their common name comes from their cycling between underwater and the surface to replenish oxygen like a diver. 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 Bifurcitus ducalis are the largest, reaching up to 4.5 and 4.75 cm (1.8 and 1.9 in) respectively, although the latter is listed as extinct by the IUCN. 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. The oldest of the species is †Palaeodytes gutta, from the Late Jurassic according to Karabastau Formation fossils.

Sialis mohri is a species of alderfly in the family Sialidae. It is found in North America.