Ecology

Adults and larvae live among fine substrates in marginal wetland situations, lakes, ponds and streams as well as coastal mudflats, dunes, shores and salt marshes although they do not inhabit sandy areas without mud or a high organic content and the ideal substrate contains between 30 and 60% water. They occur from sea-level to about 3000m; the adults are good fliers and quick to colonize suitable environments, are generally nocturnal and during the spring and summer may be attracted to light when dispersing from their usual habitat. Adults form galleries as they push through sediments consuming algae, zooplankton and organic debris, they generally work through fresh substrate but will also follow cracks in drying substrate or the burrows of other beetles etc. they usually move with the head held down against the close-fitting anterior margin of the pronotum so that the forebody is rigid and the mouthparts are protected from wear as they go, the femora are broad and flattened and act to scrape away sediment which is then pushed behind them by the tibiae which are lined externally with long rake-like setae and spurs for the purpose, and while tunnelling the tarsi are held reflexed against the upper surface to protect them. The mandibles are curved upwards with broad basal plates and robust multi-pointed teeth adapted to scraping away substrate in front of the beetle and in old specimens these will be worn down, along with the tibiae, from constant erosion. All species have dense hydrophobic hairs which prevent them from getting wet and also act as a plastron, the legs are similarly clothed in very fine and dense pubescence to prevent them from becoming clogged with sediment during tunnelling. The burrows are usually obvious from the rings of sediment piled around the entrance and often by raised lines as the beetles work their way just below the surface. During heavy rain or wave action the substrate may become flooded and then the beetles quickly leave the burrows and take flight, under such circumstances they may fly several kilometres to escape the flooding and find a suitable habitat; a good way to sample them is to flood small areas and tube them as they emerge, many will fly immediately they emerge but some will float on the surface, protected by the hydrofuge pubescence, and are easily taken. In temperate regions most species are thought to be univoltine. Eggs are laid in the spring and early summer and may continue over a long period. Females ready to oviposit may spend some time seeking out suitably boggy, almost waterlogged areas, before they lay small, spherical and pale eggs  in small groups inside specially constructed incubation chambers among the sediment, in the few species studied these are located about 25mm below the surface, and in one Nearctic species the female displays egg-guarding behaviour. Eggs hatch after a week or two and the small larvae remain in the adult burrows for a while, sometimes emerging onto the surface on warm days, before they begin to start their own horizontal burrows just below the surface, like the adults they are densely pubescent and are thought to respire, at least partly, by a plastron. They develop rapidly and pupate from mid-summer in a cell within the substrate, adults eclose after a few days and emerge from the substrate from mid-summer but later eclosing adults will remain in the cell through the winter, those early-emerging new- generation adults will return to the substrate in the autumn and construct a cell in which they will pass the winter. So far as is known neither larvae nor pupae overwinter. Adults become active early in the year, late January or February if conditions permit, and mating occurs through the spring after a period of feeding. In some areas heterocerids are a significant prey items for waders and amphibians and also play a role in seed burial and dispersal in riparian habitats. Adults often occur in very large numbers along localized marginal areas and these aggregations may contain more than one species, they leave their burrows in the evening and often disperse en masse, and at this time they may be attracted to light in numbers. The open and moist habitats frequented by Heterocerids will often host many other kinds of beetles e.g. Dryopidae, Carabidae, Staphylinidae, Chrysomelidae and Curculionidae, and so when found colonies should be observed carefully before being disturbed. Our U.K. species inhabit a wide variety of habitats; H. fossor Kiesenwetter, 1843, H. flexuosus Stephens, 1828 and Augyles maritimus (Guérin-Méneville, 1844) in salt-marshes and coastal mud-flats, H. obsoletus Curtis, 1828 and H. fusculus Kiesenwetter, 1843 in marginal mixohaline situations, and the others in various fresh water habitats.