HYGROBIIDAE  Régimbart, 1878

Screech Beetle

This small family of water beetles is represented in the UK by a single widespread and locally common species - Hygrobia hermanni.

Suborder:     ADEPHAGA Clairville, 1806

Genus:          Hygrobia

Species:        H. hermanni (Fabricius, 1775)

Size:              8-10mm

Around the World

A small family comprising six species of very distinctive water beetles included in the genus Hygrobia Latreille, 1804. One species, H. davidi Bedel, 1838, may be extinct; it is known from a male specimen collected in Jiangxi Provence, Southeast China, which is now stored in the Museum d’Histoire naturelle in Paris. Four endemics occur in Australia; H. nigra (Clark, 1862), H. wattsi Hendrich (2001), H. maculata Britton, 1981 and H. australasiae (Clark, 1862) and all are rare. The final species, H. hermanni (Fabricius, 1775), is very local but widespread throughout Europe and North Africa. They are commonly known as screech beetles due to their habit of stridulating loudly when alarmed; the sound is produced when the sharp edge of the seventh tergite is rubbed against a median subapical file on the elytral undersurface. Adults and larvae of all species inhabit stagnant water where the substrate is layered with fine mud and decayed plant debris. Both stages are predatory. The adults are characterized by the following features: Size up to 10mm. Body very convex above and below. Glabrous or nearly so and densely punctured.  Tarsi always 5-5-5. Eyes protuberant and remote from the front margin of the pronotum.  The presence of an antecoxal sclerite; a small transverse sclerotized plate lying between the posterior edge of the metasternum and the post coxal processes. The adults are strong swimmers, using alternate strokes of the hind legs as they move. The larvae are compact with a conspicuously broad forebody and large head onto which the labrum is completely fused. There is a series of setose gills between the prothorax and the third abdominal segment. They are readily separated from other water beetle larvae by the elongate terminal abdominal segment with its three long and hairy appendages.

Description

From the size and general appearance H. hermani should be unmistakable. 8.5-10mm Brown with the head laterally, the anterior and posterior margins of the pronotum and most of the elytra dark grey or black. Appendages pale. Head shiny and finely punctured, with large and prominent  eyes.  Underside  dark  yellow  or brown.  Pronotum  and  elytra

coarsely punctured. Elytra with four rows of setiferous punctures although these may be obliterated in places. All tibiae in both sexes with a pair of very long terminal spurs. Outer edges of the front and middle tibiae with long swimming hairs. Male with the second and third segments of the front and middle tarsi widely bilobed, and the claws on the front tarsi more curved when compared to the female.

Ecology

The Screech Beetle is generally common and widespread though local across Southern England and the midlands becoming much more rare further north. Typical habitat is still and stagnant water with plenty of vegetation, cattle ponds etc. and occasionally on the margins of reservoirs. Adults occur from March to October and are often found in numbers, sweeping among the accumulated bottom vegetation is a good way of finding them. They surface periodically to replenish an air bubble stored beneath the elytra and when disturbed swim rapidly down and hide among the bottom detritus and soil. Oviposition occurs from late March to July and the eggs are laid in small rows on the surface of aquatic vegetation, during the warmest part of the season they take about nine days to hatch. The crustacean-like larvae are entirely aquatic, breathing through gills and living among the bottom ooze and accumulated detritus. The main larval food is Tubifex worms. The duration of the three larval stages varies widely but the adults generally eclose between nine and fifteen weeks after egg laying. Pupation occurs out of water in an earthen cell, the pupal stage takes between two and three weeks to complete and the adult remains in the cell for a week or so after eclosion. Adults disappear during the autumn and are thought to overwinter buried in submerged soil.

Further Reading

Water Beetles of Britain and Ireland

-RES Handbook

G. N. Foster & L. Friday

Keys to family and species level. 

British Water Beetles

Frank Balfour-Browne

Classic account of all British water beetles. 

Icones insectorum Europae centralis 9

J. Hajek

Good introduction to a number of water beetle families.

The aquatic Adephaga of Fennoscandia and Denmark

Mogans Holmen

Detailed accounts of Hygrobiidae and other families.

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