Rhopalum gracile Wesmael,1852

Synonyms

Rhopalum nigrinum KIESENWETTER, 1849; Crabro kiesenwetteri MORAWITZ, 1866

Description and notes

A small, stem nesting solitary wasp. Identification keys are given in Lomholdt (1984) (as R. nigrinum), Richards (1980) and Yeo & Corbet (1995).

Distribution

Infrequently recorded from a few wetland localities in East Anglia, with very few modern records. Overseas this species is found throughout Europe and eastwards to Japan.

Status (in Britain only)

Listed as Vulnerable (RDB 2) in Shirt (1987) and by Falk (1991). Possibly under-recorded due to its habitat preferences.

Habitat

Associated with lush marshes and reed beds, both in fresh and (in Scandinavia) brackish water sites.

Flight period

Univoltine; on the wing from June to August.

Prey collected

From studies of the species in Japan, R. gracile stocks its nest cells with a mixture of small flies (Chironomidae, Psychodidae, Dolichopodidae and Tephritidae) and Psocoptera (Lomholdt 1984).

Nesting biology

No nest sites have been recorded from Britain. In Scandinavia, the species nests in the stems of reeds; in Japan nests have also been found in lyme-grass (Leymus arenarius) and goldenrod (Solidago occidentalis) (Lomholdt 1984).

Flowers visited

Angelica species.

Parasites

None recorded, though Lomholdt (1984) suggests the generalist chrysid wasp Trichrysis cyanea may be a parasite.

Author of profile

M N Smith.