Athous haemorrhoidalis (Fabricius, 1801)
Occurs throughout England and Wales including the Isles of Wight, Scilly, Lundy, Anglesey and Man; with the exception of the Severn estuary and Worcester area modern records are more sparse in the west. There are modern records scattered throughout Scotland to the far north including the Western Isles and Hebrides but it appears to be absent from Orkney and Shetland. The species is generally common and often abundant; in the past the larvae have been serious pests of a wide range of crops eg cereals, potatoes, beets and mangels although never so damaging as species of Agriotes (Gratwick, 1992). They occur throughout our Watford area and, while numbers vary from year to year, are usually abundant in a wide range of habitats. Adults are active between April and July depending on season eg we swept them from low vegetation at Radlett road during the first week of March 2009, and in most years a few adults persist into August. Their natural habitat is grassland on rather open soils; eggs are laid in small groups just below the soil surface and usually in vegetated areas that are less likely to dry out. The tiny larvae, just over a millimetre in length, emerge after a month or so and grow very slowly, taking between four and five years to reach maturity. Young larvae feed on vegetable detritis in the soil as well as living plant material but as they grow tend to feed exclusively on underground parts of living plants. Feeding is most intense during March to May and September and October, larvae reaching maturity during August when they burrow deep into the soil to pupate in an earthen cell. Adults emerge within a few weeks but usually remain in the cell to hibernate, if disturbed they will move up through the soil and hibernate elsewhere.

Although adults may be swept in numbers from grass and herbaceous vegetation in a wide range of situations, they are easy to observe in the wild as they have the habit of basking in bright sunshine on large leaves eg Docks and, more especially, nettles, usually lying along the midribs. They may also be observed basking on the flowering tips of long grass stems.

The bicoloured, elongate form and large size are distinctive and only A.vittatus Fab. is likely to be mistaken for the present species (See below).
10-15mm. Head and pronotum black, elytra mostly or entirely chestnut brown, entire upper surface somewhat shiny. Head densely punctured although this is sometimes sparse on the vertex, with pale, forwardly directed and recumbent pubescence. Eyes convex and round or with a weak sinuation behind antennal insertions. Antennae 11 segmented and dark, inserted on front of head under raised margins of clypeus. Joy separates this species from (A.vittatus) on the colour of the first antennal segment; entirely black in A.haemorrhoidalis and entirely yellow in A.vittatus, in most of our A.haemorrhoidalis this segment is dark with the base and apex reddish. First segment broad with strongly curved inner edge, second distinctly shorter than third, third slightly shorter than fourth, 4-10 weakly dentate. In A.vittatus the 2nd and third are almost equal and the third is distinctly shorter than the fourth.
Pronotum elongate and convex, width at middle about the same as that across the produced hind angles. Moderately densely punctured, at least as strong as on head but in most specimens it is stronger, punctures separated by their diameter or a little less. Pubescence directed forward, obliquely so inside hind angles. Median longitudinal depression weak (best viewed from side with strong light), extending anteriorly towards, or touching, front edge. In A.vittatus this depression is present only towards the base or may be absent. Lateral and hind edges bordered, this extends to the tips of the produced hind angles. May be entirely black but in most of our specimens the front and hind angles are dark red. Scutellum large and convex at base, coloured and punctured as pronotum. Elytra mostly chestnut brown with suture, base and lateral areas darket but this varies widely; Laibner quotes specimens entirely black with greenish lustre or entirely rusty. Parallel or nearly so in basal half, evenly narrowed posteriorly to rounded apex. Each with nine complete and punctured striae, basal margin - which continues from the sixth stria - sharply raised, the strength of this varies between specimens. Pubescence light grey to golden, shorter than that on pronotum, backwardly directed; obliquely so on the inner interstices, parallel towards the edges. Interstices flat and very finely punctate; generally four rows of fine punctures on inner interstices. Legs brown, tibiae often darker. Tarsi 5-5-5, second and third segments bilobed below, lobes of third segment covering most of the fourth segment. Last segment as long as the basal segment.

Description from 20 Watford specimens at X20

Gratwick, M. 1992. Crop pests in the UK pp 216-221 Chapman and Hall