Andricus aries (Mayr) (Hymenoptera: Cynipidae) - a gall wasp new to Essex
JERRY BOWDREY
Colchester Museums, 14 Ryegate Road, Colchester COl 1YG
Ram's-horn galls on Pedunculate Oak Quercus robur, believed to be induced by the Cynipid wasp
Andricus aries (Mayr), were first reported in Britain from Parliament H ill and otherparts of Hampstead
Heath in London (Leach & Shirley 1999). They are characterised by a single chamber up to 8mm
long and 6mm wide, which bears a horn-like outgrowth up to 50mm long.
On 6th May 2000 at Little Clacton (TM1618) the author found four such galls on a young, two metre
high Q. robur sapling, growing on the edge of a mixed deciduous hedge. Only four galls were
located, one singleton and three grouped together, agreeing with Carpenter's observation that never
more than two or three galls were found per tree (Leach & Shirley loc. cit.). All the Essex galls
showed emergence holes: the literature suggests that the adults emerge in August and September.
Fig. 1. Gall of Andricus aries © Colchester Museums
A return visit to the site on 25th October failed to locate any galls of a subsequent generation, but on
17th December a single gall of A. aries was found on an older Q. robur at Tiptree Heath (TL8814).
The gall was rendered conspicuous by the retention of a bright green colour, contrasting with the
buds and twigs of the otherwise brown tree. The gall showed no emergence hole, perhaps indicating
that it was dead, parasitised, or possibly lying dormant for more than one season.
Shortly after the Tiptree discovery, three further Essex records were received from Brian Ecott:
TQ478936 Hainault Forest 22.vii.2000; TQ431947 Roding Valley Meadows 29.viii.2000 and
TQ547976 Strawberry Wood, Navestock 30.vii.2000.
Galls of this species have in addition been found in Kent and Surrey (Leach 2000).
I would like to thank Brian Ecott for allowing me to publish his records of A. aries.
References
LEACH, C.K. (2000) Andricus aries becoming established. Cecidology 15(1): 74.
LEACH, C.K. & SHIRLEY, P. (1999) The ram's horn gall of Andricus aries on Quercus robur - a Cynipid
gall to be added to the British list? Cecidology 14(1): 18-21.
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Essex Naturalist (New Series) 18 (2001)