Helophorus grandis Illiger, 1798

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POLYPHAGA Emery, 1886

HYDROPHILOIDEA Latreille, 1802

HELOPHORIDAE Leach, 1815

Helophorus Fabricius, 1775

Helophorus Fabricius, 1775

This is a mostly central and northern European species, in older literature it is often quoted as being more widespread, occurring as far south as North Africa, but these records have subsequently been found to refer to other species; the distribution extends from Spain to the Ural Mountains although it is absent from much of southern Europe, and north to the UK and some central provinces of Fennoscandia. It is also widely established in the eastern United States and Maritime Provinces of Canada where it has been known since the early twentieth Century, presumably from specimens accidentally imported from Europe. Here it is generally common throughout Britain and Ireland north to Orkney though more local across the Highlands of Scotland and absent from some of the outer Western Isles. Adults occur year-round, they overwinter among moss etc. out of water and are active over a long season from early spring, peaking in abundance from May until July and often again in the autumn, they occur in all types of still and slow-moving water, often in temporary habitats such as flooded ruts and hollows but also in stagnant and densely-vegetated margins of ponds, reservoirs and rivers,  and during warmer periods they fly in numbers and will alight on ponds, troughs and even parked vehicles, attracted by the polarized light which they mistake for water. Mating occurs on or under the water surface or among damp marginal substrate during spring and early summer and the biology is typical of many wetland members of the genus, females deposit small numbers of eggs in a silken cocoon among damp substrate and the predaceous larvae develop among damp soil and moss etc. Larval development takes two or three weeks, pupation occurs out of water and new-generation adults appear from late spring. Further egg cocoons may appear in late summer or autumn but these will overwinter and the larvae will not appear until the spring. Sweeping in marginal habitats will often produce adults, in warmer weather they are likely to appear anywhere in the vicinity of water, especially among vegetation on damp soil when they are frequently found caked in dried soil, and because they may be very active and fly frequently they will often be seen on the surface of still water in any situation.

Helophorus grandis 1

Helophorus grandis 1

Helophorus grandis 2

Helophorus grandis 2

Helophorus grandis 3

Helophorus grandis 3

Helophorus grandis 4

Helophorus grandis 4

Helophorus grandis 5

Helophorus grandis 5

5.5-8.0 mm. Easily identified by the combination of large size, a distinct scutellary stria, smoothly-striate elytra and a square-dentate (sometimes referred to as ‘castellated’) margin to the apical sternite (which is often visible but sometimes hidden just beneath the elytra). H. aequalis C.G. Thomson, 1868 has the same combination of characters, it is generally smaller but there is plenty of overlap in the sizes and it has a more finely denticulate apical sternite, in general the forebody is less strongly granulate and the granules often merge, this character is comparative but can become obvious when considering a series of each species. In doubtful cases males can be dissected; in the present species it is >1.0 mm whereas in aequalis it is <1.0 mm. Most specimens of grandis have a rather typical appearance; the head and pronotum are dull metallic green or golden green with well-defined and discrete granules, and the elytra are extensively dark and have a distinct oblique impression in the anterior third.

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