Biology. - According to Plant (pers. comm.), a typical species of narrow ditches with slow flowing water in southern and eastern England; swarms have been observed several times in a ditch by a tall hedge in an otherwise open situation, in a pool behind a marine shingle bar in Dorset, or over stagnant pools on a track in the sunshine; many males were skimming the surface of the pool, scavenging insects trapped on the surface, and if injured insects were dropped on to the surface they were immediately pounced upon by males. However, males have never been observed by Plant flying with prey, even in compact nearby swarms of several hundred individuals that are only a few cm away from the skimming males; motion in the swarms was rather slow, and entire swarms retreated to nearby bushes when a slight wind occurred. Mating takes place in the swarm and copulating pairs remain in the swarm, definitely without any prey or any silk object transfer. On brackish coastal grazing marshes in Somerset, males commonly swarm in deep ditches according to Plant, for instance in the open over Lemna covered ditches and under the deep shade of bankside vegetation.