As the common name suggests, this family are similar in appearance (and closely related) to the Elateridae: elongate parallel-sided beetles with pointed pronotal hind angles and unclubbed antennae, though Eucnemids have a noticeably weaker clicking mechanism.  Like the Elateridae, larvae of the Eucnemidae feed in dead wood.

There are seven species in Britain, but as small, secretive woodland beetles it is entirely possible that more remain to be discovered (three of the seven current British species were only discovered post-1950).

One species in Britain, Ptilodactyla exotica Chapin which has been found breeding in moist soil in glasshouses at Kew and the Cambridge University Botanic Gardens.  Flattened, brown beetles with long feathered antennae, they are thought to feed on the spores and hyphae of microfungi on vegetation.

Only one species in Britain, Eubria palustris Germar, which is 2-3mm long and looks rather like a black, flattened ladybird with long threadlike antennae.  Found most commonly in the splash zone of fast-flowing water, adults are short-lived and the aquatic larvae are more commonly found.  These are known as ‘water-pennies’, due to their bronze colouration and flattened, rounded chiton-like appearance as they cling on to rocks and logs, where they eat algae.  

There are 8 species of Heteroceridae in Britain, all 2-5mm long with fossorial legs and pubescent elytra.  Most species are restricted to saltmarshes, although others live in the banks of rivers and ponds.  Adults live in shallow tunnels that they dig through bankside mud, but also fly well and come to light. 

The beetles are elongate, with an obvious waist between the pronotum and elytra, which usually have a variegated pattern of light yellow-brown interspersed with dark brown.  All members of the family are virtually impossible to reliably determine on outwards appearance, and almost always require dissection of the males.

Only one species in Britain, Limnichus pygmaeus (Sturm), a 1.75mm oval beetle found on wet rocks in the splash zone of running water.  Morphologically very similar to the pill beetles (Byrrhidae), the species is dark brown to black, oval, hairy and strongly convex, and can withdraw all appendages tightly against the underside of the body to play dead.

Represented in Britain by 9 species, all 3-6mm long.  Most occur in semi-aquatic habitats, particularly wet mud, and only one species is fully aquatic: Pomatinus substriatus (Müller), which is found in deep streams.  Dark in colour, oval to elongate and with prominent tarsal claws, they can appear similar to Elmidae but have short antennae with a pectinate club, rather than that family’s long threadlike appendages.

Generally found amongst stones and gravel in the riffles of fast-flowing rivers and streams, there are 12 British species.  All are 1-5mm long and walk on the substrate rather than swimming: indeed, that have to hold on to the substrate due to their positive buoyancy, and if disturbed will float to the surface.  Adults are dark brown to black and oval to elongate, with striate elytra, large tarsal claws and long threadlike antennae.  Away from riffles, Elmidae may be found amongst stones on lake shorelines, slow-flowing sections of rivers and drains, and on submerged logs.  

There are 13 short, stout, 1-10mm Byrrhidae in Britain.  They get their common name from their habit, when disturbed, of folding all their appendages into grooves on the underside of the body and playing dead, giving the appearance of a seed or pill.  Generally found in litter and moss or under stones, they are largely a heathland/moorland group.  Both adults and larvae are thought to feed on mosses.

One of the more famous beetle families due to the bright metallic colours of some of the tropical species, there are just 17 species in Britain and most are restricted to the south of England.  They are elongate, parallel-sided beetles, 2-12mm long and tapering to a point at the posterior end: many are metallic green.  Larval exit holes in wood have a characteristic D-shape and are often the first clue to the existence of a colony. 

Eleven species are saproxylic: in particular Melanophila acuminata (De Geer) is the only resident beetle species to be associated strongly with fire-damaged wood, and can be found on lowland heathland.  Six species (Trachys and Aphanisticus spp.) have larvae which mine leaves or stems. 

One species in Britain which is quickly recognised in the field.  Dascillus cervinus L. is 8-12mm long with a broad, slightly flattened elongate form and strongly-bilobed tarsi.  Widely distributed but local, the beetles climb vegetation before flying and can be found relatively easily by eye during the summer months.  Larvae are soil-dwelling root eaters.