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Melinda cognata Meigen 
II. LIFE-HISTORY OF MELINDA COGNATA MEIGEN 1 
PARASITIC IN HELICELLA ( IIELIOMANES ) 
VIRGATA DA COSTA. 
Last year I found in and around Cambridge the larvae of M. cognata living 
in a small snail, H. virgata. I was able to determine the relation between the 
parasite and the host, to follow the complete life-cycle of the fly, and to study 
r 
the anatomy of its larva. 
(a) The host. 
Helicella ( Heliomanes ) virgata da Costa is a small snail varying greatly in 
size, shape and colour. It is very common in England, Wales and Ireland, and 
it occurs in France, Corsica, etc. It is gregarious and often appears in thou¬ 
sands covering the pastures and the hedges. In this connection the following 
statement of E. Steep (1901) is of interest. 
The Banded Snail is widely distributed in England, Ireland, and Wales, but in Scotland 
appears to be found only in Ayrshire. It is most abundant along the south coast, especially 
in Cornwall, on Dartmoor, and along the South Downs. To get an accurate idea of its 
profusion in these parts it is advisable to walk out on the pastures after heavy summer 
rain; then one can excuse the local idea that these snails come not from among the herbage 
but from the heavens, as though they were hailstones. Fences, gates, stones, thistles, and 
grass stems are so thickly coated with them that one marvels how it is possible for them to 
find cover or food at other times. These molluscs have long been regarded as the source of 
the flavour peculiar to the Down mutton, but I think it is usually considered that they are 
eaten inadvertently by the sheep in cropping the short grass. I am assured by intelligent 
Cornish farmers, however, that this is not so: when sheep are turned out to feed on the cliff- 
pastures they make by preference for those parts near the edge w T here the “ sheepsnails' 1 '’ 
(H. virgata and H. acuta) are most plentiful, and they thrive exceedingly upon them. They 
do not appear to hibernate. Full-grown specimens measure a little more than half an inch 
across. 
According to Macquin-Tandon (1855) H. virgata lays in autumn 30-60 
eggs from which the young hatch in 15-20 days. They become adult in the 
middle of the second year. 
The specimens used for this study were collected in or near Cambridge in 
the following places: hedgerows in Grange Road, Barton Road, Grantchester 
Road, along the footpath from Grantchester to Barton, Madingley Road and 
1 As previously mentioned, the flies of Melinda which I bred from snails were identified by 
Mr C. J. Wainwright to be the common species M. cognata Meig. Since, on the other hand, the 
type of M. cognata Meig. has not been recently examined, Mr Wainwright thinks it is important 
to specify that this common British species is what Kramer and Villeneuve regard as cognata and 
which Strobl and Schinei called gentilis Rob.-Desv., but that it is not the species which the latter 
describe as cognata. 
M. cognata of Schiner and Strobl corresponds to gentilis Rob.-Desv. as described by Verrall 
(Ent. Monthly Magaz. 1912, p. 192). Until Meigen’s type is examined, to place the identity of my 
specimens bejmnd doubt, Mr Wainwright advises me to call them M. cognata (Meigen?) Kramer 
= gentilis Schiner and Strobl). 
