2002 update on Odynerus simillimus in north-east Essex
even if the foodplant were known, as they have been paralysed by the wasp's sting. Identification,
therefore, has to be from the larva alone. Odynerus simillimus appears to confine itself to weevil
larvae of the genus Hypera, and these have been identified as either H. pollux or H. rumicis. In the
Essex localities H. rumicis, a Rumex feeder seems more likely. However, although the wasps seem
to have no difficulty in finding Hypera larvae, the best rate so far being one every eight minutes, it
has so far been vastly more difficult for the entomologists! A great deal of sweeping, beating and
hand searching in 2002 produced no Hypera larvae at all. Yet at Rickling Broad when one nest
containing four chambers was excavated, one apparently complete chamber contained 19 weevil
larvae (Harvey 2002). 4x19x57 is an awful lot of larvae from an area, and although no Essex
nesting aggregation yet found has been so large, there must be plenty of Hypera larvae somewhere.
Moreover the nesting period is not long, about eight weeks from late June, so there has to be a
reasonable abundance of prey during this period. H rumicis larvae are apparently ectophagous,
mostly on the flower heads, although these can be looking a bit dead and uninviting by mid-August,
particularly in a dry summer. Therefore, seeing a wasp actually catching a larva and preferably
leaving one behind for us as well, would be a great help.
Single specimens of O. simillimus were found in Suffolk at Snape Maltings in 1999 and near
Minsmere in 2001. A small nesting aggregation was confirmed in 2002 at Shoebury in south Essex
after a single male had been found in 2001 (Harvey 2002), and it seems quite likely that the wasp
could be found elsewhere in Essex, East Anglia and the south-east, most probably near the coast.
The small aggregations of mud chimneys are distinctive and most likely to be found on flat or
sloped exposures. The only two similar species are the Nationally Scarce O. melanocephalus, a
rare wasp present in Essex and the commoner O. spinipes, whose mud chimneys, usually on vertical
banks, are much longer as well as being curved downwards. I am sure Peter Harvey would be
pleased to hear from anyone finding what could be an O. simillimus or the similar O. melanocephalus
nest aggregation.
Although there is great appeal in the idea that O. simillimus might have been occupying the same
few square yards of Alresford since Harwood found it a century ago, it is beginning to look as
though the wasp is just as liable to move readily within an area. It still seems though that the wasp
has probably been present in the general area in the Colne Estuary the whole time.
References
HARVEY, P.R. (2002) A.C.G Cerceris quinquefasciata. Cerceris quadricincta & Odynerus simillimus
Project 2002. Report for the Aculeate Working Group.
HARVEY, P. & SCOTT, D. (2001) Odynerus simillimus Morawitz, R, 1867, rediscovered in Essex. Essex
Naturalist (New Series) 18: 60-62.
SHIRT, D.B. (Ed.) (1987) British Red Data Books 2. Insects. NCC, Peterborough.
Essex Naturalist (New Series) 20 (2003)
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