BRITISH HARVEST-SPIDERS 187
Group (c): species which live above the field layer on bushes,
trees, walls, fences and other man-made structures. Their
young fall within groups (a) and (b).—Oligolophus agrestis
(Meade), O. hansenii (Kraep.), Odiellus spinosus, Opilio parietinus
(Degeer).
There is some overlap between these groups :
(1) L. rotundum and occasionally L. blackwallii may sometimes be
found on walls, bushes, trees, etc.
(2) M. morio is occasionally found on walls and bushes and trees,
more especially I believe in the North.
(3) P. opilio sometimes goes on to walls, bushes and trees.
(4) O. agrestis, though more frequently inhabiting bushes and trees,
also lives in the field layer, in fact it is forced to do so in some places
as for example, on Skokholm Island, where there are no bushes or
trees.
MIGRATION
It can be seen from the foregoing that certain species migrate
upwards as they mature. This appears to be associated with the
need for bigger prey, more space to move in, mating and probably
a different temperature and moisture requirement. Dr. Todd
(unpublished) has shown that in certain species an upward migra-
tion on to trees during the night is associated with the damper
upper air.
There must be a downward migration of the group (c) species
for egg laying though I have not observed this. I do not know
when or how often it occurs. The same is true of the group
(b) species but here the distance is so short I hesitate to call it
migration.
LATERAL DISTRIBUTION
Of our twenty-one species, eighteen have been recorded in
Essex. It is likely that Trogulus (Plate 13 (c)) and Anelasmocephalus
(Plate 13 (d)) occur in this county. The former is commonest on
chalky soils, the latter apparently confined to them.
The following county records are in addition to those recently
published by Dr. Bristowe (ibid.):
A. cambridgei : Wilts.
N. lugubre : Wigtown, Peebles, Selkirk, Roxburgh, Shetlands.
N. chrysomelas : Monmouth, Glamorgan, Carmarthen, Denbigh, Flint,
Wigtown, Kirkcudbright, Dumfries, Peebles, Selkirk, Roxburgh,
Fife, Aberdeen, Banff, Elgin, Ross, Sutherland.
L. blackwallii : Glamorgan, Northumbs., Haddington.
M. morio : Hants., Monmouth, Hereford, Pembs., Wigtown, Peebles,
Selkirk, Roxburgh.
L. ephippiatus : Bucks., Glos., Monmouth, Glamorgan, Carmarthen,
Pembs., Shetlands.
O. spinosus : Bucks.
O. meadii : Essex, Flint.
O. tridens : Hants., Wilts., Carmarthen, Durham, Wigtown, Dumfries,
Peebles, Selkirk, Roxburgh, Fife, Aberdeen, Banff, Inverness, Ross.