Crawling Water Beetles

Includes several very common species likely to occur in most freshwater situations throughout the year.

ADEPHAGA Clairville, 1806








Around the World

These small water beetles are so very distinctive as to have been formerly classed as the only family within the superfamily Haliploidea Aube, 1836 although they are now more generally included within the Caraboidea. They are an almost cosmopolitan group of about 220 species included in 5 genera and there is a further genus, Cretihaliplus Ren, Zhu & Lu, 1995 known from 2 cretaceous fossil species discovered in Mongolia.

  • Algophilus Zimmerman, 1924 contains only a single species, A. lathridioides Zimmerman, 1924 from Africa, which is superficially similar to Brychius Thomson, 1859 species; small, 2.2mm and drab with large eyes which make the head as wide as the pronotum, at least near its base. The dorsal surface is rather finely punctured and the anterior margins of the clypeus and labrum are rounded, the terminal segment of the palps is about half the length of the penultimate. The pronotum is strongly sinuate laterally and constricted in the basal half, with transverse series of punctures behind the anterior margin and 2 transverse series of very strong punctures near the base, the elytral punctation is fine and random.

  • Apteraliplus Chandler, 1943 also contains a single species, A. parvulus (Roberts, 1913), from the western United States and known from only a few sites. Originally placed in Brychius but quite distinct from that genus; small, 2mm, dull brown and elongate with the head narrower than the pronotum and large, convex eyes. The pronotum is broadest at the base and strongly punctured over the disc; the elytra are elongate with strongly punctured striae but lack a scutellary stria. Distinct among the Haliplids in lacking raised lines or carinae on the lateral margins of the Prosternal process.

  • Brychius Thomson, 1859 includes 5 species of which 3 are Nearctic although one, B. hungerfordi Spangler, 1954 is critically endangered with almost all individuals living in a single locality in Michigan, it is thought to be flightless and surveys from 2004 and 2010 suggest that only about 1000 remain in the wild. Two species occur in Europe; the widespread central and northern species, B. elevatus Panzer, 1794, which is the type and also occurs in the U.K., and B. glabratus (Villa & Villa, 1835) which is more southern, occurring in northern Italy.

  • Peltodytes Regimbart, 1879. With the exception of Australia and South America this genus is represented worldwide. There are about 35 species included in 2 subgenera; Peltodytes S.Str. with 13 and Neopeltodytes Sato, 1963 with 22. Although widely distributed in the tropics this genus is most diverse in temperate regions; 18 occur in Canada and the USA. Most of the species are very similar and they can be difficult to identify, but of the two European species only the type, P. caesus Duftschmidt, 1805 occurs in the U.K. and so identification is straightforward.

  • Haliplus Latreille, 1802 includes most of the species; more than 170 are included in 6 subgenera:

    • Haliplidius Guignot, 1928 includes 5 species, 3 from the U.K.

    • Haliplus s.str. includes about 30 species, 8 from the U.K.

    • Liaphlus Guignot, 1928 includes about 105 species, 5 from the U.K.

    • Neohaliplus Netolitsky, 1911 includes 6 species, 1 from the U.K.

    • Paraliaphlus Guignot, 1930 includes 18 species, none from the U.K.

    • Phalilus Giugnot, 1935 includes 2 species, none from the U.K.


The widest diversity occurs across the Holarctic region, and particularly in Asia; about 70 species occur in the Nearctic region.


Morphologically the family is not very diverse; they are distinctive and the 3 widespread genera, which are represented in the U.K., represent the group as a whole. There are no other families even remotely similar and so specimens can be placed with confidence. Identifying the species is another matter, even within the limited U.K. fauna this is not always possible; many can be identified on external morphology as there are good ventral and dorsal characters, however members of the ruficollis group , which unfortunately contains some of our commonest species, e.g. H. ruficollis (DeGeer, 1774), H. sibiricus Motschulsky, 1860 and H. immaculatus Gerhardt, 1877 will need to be dissected and then only males are straightforward, the females being identified, if at all, by association. Finding members of all 3 genera should be possible; at least 8 species of Haliplus are common and widespread, and more should be expected with a little work, Peltodytes is widespread in the south, and Brychius is widely distributed though local.

These are small and characteristic water beetles; 2-5mm and elongate-oval or sometimes rather parallel-sided, and continuous in outline, glabrous or with scattered very fine hairs and the underside convex and lacking hydrofuge hairs. They are drab, some shade of brown to almost yellow, and with various darker markings which are distinct and symmetrical on the elytra. The head is densely and often coarsely punctured with large, convex eyes and 11-segmented and filiform antennae. The palps are useful in identifying the genera; in Haliplus the terminal segment is shorter than the penultimate while in Peltodytes it is longer. The temples are long but generally hidden under the pronotum. With the exception of Brychius the pronotum is broadest at the base and strongly tapering towards the anterior margin, the lateral margin is finely bordered and the base is strongly sinuate. In most cases it is, at least to some extent, strongly punctured, and there is often a ridged furrow at the base opposite the fourth or fifth elytral stria, it is generally short except in H. lineatocollis where it extends almost to the centre. Brychius is very different; here the pronotum is broadest in front of the middle and so strongly sinuate laterally. Scutellum hidden. Elytra broadest anteriorly or about the middle, to almost parallel-sided, usually with 10 punctured striae and variously punctured interstices; in Brychius with raised longitudinal ridges. Characteristic of the family are the greatly expanded metacoxal plates which are immobile although not fused and cover the base of the abdomen, the meta-trochanters and the femoral bases; they are used to trap air when the insect is submerged. These plates restrict the leg movement to the horizontal plane and when swimming they move the hind legs alternately which earns them their common name. Unique among the Adephaga the hind wings are not folded under the elytra but rolled together. The prosternal process is broad and long, extending to the base of the metacoxal process, truncate and often characteristically sculptured and margined. The metasternum has a complete transverse ridge. Legs long and slender, the front tibiae without an antenna-cleaning notch, tibiae and tarsi not flattened, meso- and meta-tibiae and tarsi with long swimming hairs. Tarsi 5-5-5, the form of the segments and the claws are sometimes diagnostic. Males can be distinguished by the dilated front tarsal segments which are furnished beneath with pale ‘sucker hairs’ which are obvious at X40.


The larvae are long and slender with terminal cerci and external gills which are either long and filamentous or, in Peltodytes, only short microtrichial extensions, they are present on all but the terminal 2 abdominal segments. The third (final) instar larva has functional spiracles on the mesothorax and the first seven abdominal segments. The mouthparts are unique; the maxillae and labium are adapted to manipulate algae while the mandibles have a narrow channel through which the contents of algal cells are sucked. They are not free swimming but move slowly through the water or among aquatic vegetation.


Adults occur year round and several species are generally abundant so they should soon become obvious. They occur in all types of still and slow-moving water; ponds, canals and lake margins etc. and even brackish environments, they generally inhabit well-vegetated areas and will often be found to be common. Through the winter they may be found on floating debris or under partly submerged logs etc. and they turn up regularly in flood refuse and extraction samples from marginal habitats. Placing small branches in the water for later examination is a good way of recording them, especially in the winter and spring. Adults can remain submerged for long periods utilizing air trapped under the elytra and the coxal plates as a plastron, if kept in a beaker they will often be seen to surface, penetrating the water with the abdomen in order to replenish this air. They fly well and often turn up in light traps placed in suitable situations. Some species are more specific regarding habitat; H. apicalis Thomson, 1868 is a brackish water species while H. confinis Stephens, 1828 and H. obliquus (Fabricius, 1787) feed on stoneworts in hard water streams. Adults are omnivorous, feeding on algae e.g.  Chara & Spirogyra and aquatic plants e.g. Ceratophyllum, small crustaceans and insect eggs etc., H. lineatocollis is a specialist feeder on hydrozoans polyps. The larvae feed exclusively on algae. Haliplus species usually bite into aquatic stems to form oviposition cavities while Peltodytes lays eggs directly onto stems and leaves. The larvae pass through 3 instars before leaving the water to construct a chamber among soil or roots in which to pupate.

UK Species

Haliplus confinis

H. obliquus

H. varius

H. apicalis

H. fluviatilis

H. furcatus

H. heydeni

H. immaculatus

H. lineolatus

H. sibiricus

H. flavicollis

H. mucronatus

H. variegatus

All text on this site is licensed under a Creative Commons Attribution 4.0 International License.

For information on image rights, click HERE.