Agabus nebulosus (Forster, 1771)
Widely distributed and locally common throughout Europe north to the UK and southern provinces of Fennoscandia, this species also present across North Africa and extends east through Iran, Asia Minor and Russia into Central Asia. It is common throughout England, and Wales and across the south of Scotland and less so further north where it has a mostly eastern distribution although it also occurs on the Western Isles, Orkney and Shetland, it is also widespread and locally common throughout Ireland. Typical habitats are small stagnant water bodies, often ponds, ditches or reservoir margins on heavy soils with little vegetation although they also, if rarely, occur in brackish water pools. Adults are present year-round and are good fliers, they will often be found in new habitats or in ponds on disturbed ground or those that dry up during the summer, and at this time they will enter deep cracks in the soil or rest under logs or debris where it is permanently damp, They become active very early in the year and may be found at light or in flight interception traps through the spring and summer, they mate in the spring and the predaceous larvae develop through the summer; the fully-grown third instar leaving the water to pupate among marginal substrate from June until the autumn. Fresh adults appear over a long season from (at least) August, e.g. we have recorded them during November in our local park in south Herts, and these will go on to overwinter. Adults are easily sampled by sweeping the margins of ponds etc. but they might also occur under debris on dried up pond beds in the summer, thus we found them locally in numbers under logs and stones along with several Agabus bipustulatus and Ilybius fuliginosus during July and August, and freshly emerged specimens may be found on the soil near the water margin as they usually remain in place for some time before entering the water.
8.2-8.6mm. Adults are very distinctive due to the dorsal colour pattern. Head black or dark grey with the clypeus, labrum and two variable spots on the vertex pale brown, pronotum pale yellowish-brown with the anterior margin lighter and two dark discal spots, elytra translucent pale brown with random darker markings that are variously confluent and often form irregular dark longitudinal networks, the basal margin and the basal third to half of the lateral margins are usually pale and free of darker markings. Dorsal microsculpture consists of small irregular meshes, most enclosing a very fine puncture, these are usually more strongly developed in the female, and several longitudinal series of large punctures on each elytron. Antennae pale, usually with only the last segment darkened apically, palps pale with the terminal segment darkened. Ventral surface substantially black, the hypomeron and epipleura pale brown or yellowish and the metacoxal process and posterior and lateral abdominal margins brown, sometimes only narrowly so, in some continental specimens the abdomen is completely dark. Legs entirely pale brown. Meta-tarsal claws equal in length, basal pro- and meso-tarsal segments broader in the male.
Agabus nebulosus 1
Agabus nebulosus 2
Agabus nebulosus 3
Agabus nebulosus 4
The only UK species likely to cause confusion is A. conspersus (Marsham, 1802), but this species lacks the dark spots on the pronotum- the pronotum may be extensively and diffusely darker but there are no discrete dark spots- and has the legs darkened towards the base, especially the hind femora.