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(fragment of the Key to
freshwater invertebrates of
Russia and adjacent lands
Larvae and adult beetles of the majority of aquatic species of the suborder Adephaga inhabit in water and leave water bodies only for migrations and wintering. Representatives of the suborder Polyphaga having aquatic larvae are quite common also in land stations; adults of all marsh beetles (Scirtidae) live out of water, whereas adults of leaf beetles (Chrysomelidae) and weevils, even though they can live in water, most frequently occur above water surface. Larval development normally falls on spring and summer, with monovoltine cycle, although the development of some predacious diving beetles continues for 2 years (e.g. species of the genera Agabus and Ilybius). Wintering larvae occur mostly among several predacious diving beetles, crawling water beetles and riffle beetles (Elmidae). Nearly all aquatic forms pupate out of water bodies inhabited by larvae or above water surface (Noteridae, Elmidae, Chrysomelidae and Curculionidae can pupate in water). The majority of larvae make pupal cell or even weave a cocoon near water surface on floating plants.
There are two types of breathing in adult beetles. The majority of imaginal representatives of the suborder Adephaga retain air beneath elytra and breath atmospheric oxygen or bubbles released by algae in water. Other adults keep air film on the lower surface of the abdomen, which functions as gills. Air film in these beetles is renewed out of water and is retained because the abdominal surface is not moistened. Larvae never have air reservoirs on body surface. Owing to gills larvae of whirligig beetles and water scavenger beetles the genus Berosus are totally independent of the atmospheric air; larvae of leaf beetles, weevils and noterids extract air from airways of plants, others obtain air near water surface. Larvae of some speices living near water never immerse into water for a short time, do not have any adaptations to breathing in water (Ptilodactylidae).
Larvae inhabit both large water bodies and small water bodies retaining water during a certain period. On the whole beetles are more abundant in shallow stagnant or slowly running water bodies with lush vegetation, although different groups differ essentially in their preferences. Beetles are a characteristic component of fauna of temporary water bodies where there larvae may develop. The majority of species inhabit fresh waters, but some occur also in brackish waters (e.g. Hygrotus spp.). As a rule they inhabit pure water bodies and are quite frequently associated with a particular type of ground or particular type of vegetation in a water body and some to high mountatin waterbodies. A number of predaceous diving beetles (Dytiscidae) and other beetles are typical acidophiles and prefer pit bogs. Some, for instance Agabus lineatus, are adapted to inhabiting steppe temporary water bodies and occur exceptionally in spring after drying of a water body burrow into mud until the next inundation of the water body. A large number of species of different families (most frequently on larval stage) inhabit ground and litter at water's edge (species of the genera Georissus, Cercyon) and many other water scavanger beetles, Elmidae, Dryopidae, Limnichidae, which are associated with stones of running waters (some Psephenidae and representatives of the suborder Myxophaga). Eventually some beetles are sufficiently stenobiont to be indicators of certain types of water bodies.
The majority of aquatic beetles are predators on other invertebrates, mostly insects, crustaceans, molluscs and oligochaetes, although some may attack tadpoles and alevins of fishes or consume eggs of fishes and amphibians. Larvae mostly actively attack their prey and seldom feed on fungi and plants only, adults are quite frequently scavengers or are mostly phytophagous. Larvae of fireflies inhabiting near water's edge (species of the genus Luciola) are normally specialized predators for molluscs; their adult individuals do not feed. Water leaf beetles and weevils feed exclusively on plant food; crawling water beetles, representatives of the suborder Myxophaga, Hydraenidae are mostly algivorous; Scirtidae, Elmidae, Dryopidae and Limnichidae select and filter algae and other small organisms from water, surfaces of plants and other objects immersed in water and also detritus. Large species (Dytiscus, Cybister) can cause serious damage to fishery. Many species (Rhantus spp., Eretes sticticus) have been noted to exterminate larvae of mosquitos, malaria mosquitos included. Larvae of predacious diving beetles of the genera Acilius and Graptoderes feed mainly on plankton. Moveable larvae of beetles are frequently consumed by other invertebrates. For protection against predators many beetles have developed glands secreting repellent substances.