[3] They have short, but sharp mandibles and immediately upon biting, they deliver digestive enzymes into prey to suck their liquefied remains.

[4] Like most other water beetles, adult Dytiscidae have an oval habitus, often tapering toward the head with the pronotum widest at the base.

The head, thorax, and abdomen are all streamlined; that is, they are integrated into a single, overall cohesive oval, as opposed to the three visibly articulate sections of some Carabidae like Brachinus.

All known diving beetles except ones in the genus Celina have the scutellum concealed, with only a minuscule part seen from the surface.

Diving beetles’ shape is optimized to ease navigation through water by reducing drag and improving stability while swimming.

[14] Like other water beetles, adult Dytiscidae get their oxygen while swimming by storing air in a space between their elytra and abdomen.

[15] Deronectes aubei and other smaller Hydroporinae have specialized setae on the elytra, pronotum, and ventral side that act as tracheal gills.

Another feature acting as a gill in diving beetles is a small air bubble pressed out from the subelytral cavity and held by the hydrofuge hairs at the tip of the abdomen.

The bubble shrinks over time, requiring the beetles to surface periodically due to gas exchange decreasing.

The power stroke’s function is to increase propulsion by means of maximizing the beetle’s cross-sectional area, which involves stretching the tibiae and tarsi and spreading out the setae.

Their taste receptors are concentrated on the maxillary and labial palpi, and they can detect sweet, sour, salty, and bitter chemicals.

[18] From their pygidial gland, medium and large-sized species can secrete two types of substances: one a fluid and the other a paste-like solid.

Underwater, diving beetles apply them to sensitive body parts like spiraculi and subelytral tergal respiratory surfaces to protect them from water.

Chemically, the secretion-grooming paste consists of benzoic acid, a glycoprotein, and some phenols, particularly methyl p-hydroxybenzoate and p-hydroxybenzaldehyde.

[22] Small species do not have chemical defenses, so instead opt to avoid danger by reducing their activity underwater or dispersing themselves when in groups.

Select Hydroporinae species live in terrestrial habitats, such as dry forest floor depressions, at least in the adult stage.

Some species in Africophilus, Agabus, Fontidessus, Hydroporus, Hydrotrupes, and Platynectes are specialized for living in hygropetic habitats.

[34] On land, the gait of many adult diving beetles appears awkward or clumsy due to their enlarged hind legs.

[35] When they need to colonize a new habitat for mating or better conditions, they fly and look for light reflections from the water surface.

Instead they liquefy their food through their pincers and digestive protease enzymes and use a cibarial-pharyngeal sucking pump to ingest it.

The ability of adults to cut into plants with their ovipositor is unique to the genera Agabus, Coptotomus, Cybister, Dytiscus, Hydaticus, Ilybius, Laccophilus, and Thermonectus.

Remnants of C. explanatus were found in prehistoric human coprolites in a Nevada cave, likely sourced from the Humboldt Sink.

In the Guangdong Province of China, the latter species, as well as C. bengalensis, C. guerini, C. limbatus, C. sugillatus, C. tripunctatus, and probably also the well-known great diving beetle (D. marginalis) are bred for human consumption, though as they are cumbersome to raise due to their carnivorous habit and have a fairly bland (though apparently not offensive) taste and little meat, this is decreasing.

For example, species such as Rhantus bistriatus and Graphoderus bilineatus went extinct in Britain likely because of the drainage of the Whittlesea Mere.

Their flourishing started after rice producers switched from the conventional method of draining the land midseason while it is flooded, to no-till.

[49] Dytiscid adults are eaten by many birds, mammals, reptiles, and other vertebrate predators, despite their arsenal of chemical defenses.

In the European Union, two species of diving beetles are protected by the Berne Convention on the Conservation of European Wildlife and Natural Habitats, and thus serve as umbrella species for the protection of natural aquatic habitats: Dytiscus latissimus and Graphoderus bilineatus.

According to the narrative, upon finding nowhere to rest in the "liquid chaos" the beetle brought up soft mud from the bottom.

[43] The effect of that habit has not been tested, but it is notable that the pygidial and prothoracic defense glands of diving beetles contain many types of bioactive steroids.

[51] Beetles in these two families are known as “yewha inat” (mother of water; Amharic የውሃ እናት[52]) in Tanzania and rural regions of Ethiopia.