THE SOIL FAUNA: ANTHROPODS - The Soil - page 73

F IG. 25
Distribution map of the woodlouse Platyarthrus hoffmannseggi which is often associated with nests of the
yellow ant Lasius flavus. (Data compiled by Isopoda Study Group; drawing by S.V.Green.)
This compilation resulted in a topic which gave a distribution map of each spe-
cies in the British Isles and quantitative data on the habitats in which it had been
found. Maps showing the distribution of three soil species are shown here. There is
inevitably a good deal of bias in the records as some places are searched more easily,
such as litter, dead wood and stones, as compared with places like rock crevices, soil
or shingle. Nevertheless, one can now pick out about 18 species that are often found
at some depth in the soil.
Seven of these species are entirely or predominantly coastal. Together with the
intertidal sea-slater Ligia oceanica , which is widespread on rocky coasts, they suggest
a way in which the group as a whole may have colonized the land from fully marine
habitats to the supra-littoral zone. These coastal species are found on sandy shores,
shingle, boulder beaches, salt marshes or sand dunes. Sand dunes form a bridge to in-
land habitats, for 20 species are found here, nearly 60 per cent of the British fauna.
Buddelundiella cataractae was first discovered in Britain in 1983 in a garden in
Cardiff, but has since been found in shingle, down to 80 cm deep, on the north west
coast of Norfolk. This suggests that it may occur elsewhere around the coast. Being
white, however, like many soil species, and rarely above 3 mm in length, it is diffi-
cult to see among sand grains, especially when it rolls into a ball. Moreover, shingle
is a particularly difficult material to search, so without some clues to likely microsites
the prospect of finding such a rare species is daunting. Trichoniscoides saeroeensis
has been found more widely around the coast of Britain and Ireland ( Fig. 24 ). It is
essentially a soil or deep litter woodlouse of the supralittoral zone at and a litle above
extreme high water mark. This species is often quite abundant once you find the exact
microsite.
What appeared to be an obvious case of recorder bias was seen in the early re-
cords of Trichoniscoides albidus ( Fig. 24 ). This species was widely recorded in Bed-
fordshire but rarely elsewhere. The distribution pattern reflected the activity of one in-
dividual, A.J. Rundle, and his particular ability to recognize and search suitable sites
such as wet soil on the sides of ditches and culverts and on stream and river banks.
Similar collecting methods applied in other counties by other competent recorders
produced only a thin scatter of records. More recent records in the London area and
in Kent are still largely due to his efforts but there are now other records from East
Anglia and up the east coast.
The last map ( Fig. 25 ) shows a southern or lowland bias which is seen to a great-
er or lesser extent in several species. Platyarthrus hoffmannseggi is an interesting case