Screech Beetle

The screech beetle is a small, distinctively shaped aquatic beetle found in muddy ponds across parts of Europe. It forms its own small family, Hygrobiidae, and is easily told apart from other water beetles by its rounded, highly convex, boat-like body and its habit of producing an audible squeaking or screeching sound when disturbed or handled, produced by stridulation between internal body segments rather than through the mouth.

Both adults and larvae of the screech beetle are predatory, feeding chiefly on bloodworms (midge larvae) and other small invertebrates found in soft pond mud. The species favors still, nutrient-rich, often slightly murky water with a silty bottom, and while it can fly, it is most often encountered swimming or resting near the muddy substrate of shallow ponds and ditches.

• Small, strongly convex, oval body, dark reddish-brown to blackish with faint yellowish mottling
• Distinctly domed, almost beetle-shell-like profile compared to the flatter shape of diving beetles
• Produces an audible squeak when handled, caused by rubbing internal structures together (stridulation)
• Short legs adapted for swimming in soft mud rather than open water
• Larvae are elongated and pale with prominent mandibles, quite different in shape from the rounded adult

Screech beetles inhabit still, often muddy or silt-bottomed ponds, ditches, and slow ditches with organic debris, typically in lowland areas of Europe. They are most active from spring through autumn and shelter in bottom mud during colder months.

Both larvae and adults are predators, with midge (chironomid) larvae, commonly called bloodworms, forming a major part of their diet, along with other small invertebrates found in soft sediment. The beetle's signature squeak is thought to serve as a startle response when a predator or curious hand picks it up. As predators of midge larvae, screech beetles contribute to natural population control of these abundant pond insects.

Females lay eggs in or near soft pond mud, and the hatched larvae are active predators that burrow through sediment hunting midge larvae and other small prey. After several larval instars, the mature larva leaves the water to pupate in damp soil at the water's edge. Adults emerge to resume an aquatic, predatory life, and the species typically overwinters as an adult buried in bottom mud.