THE SOIL FAUNA: ANTHROPODS - The Soil - page 75

F IG. 26
Glasshouse symphilid Scutigerella immaculata. (Photograph Broom's Barn Experimental Station.)
The vernacular name millipede implies a thousand feet but the maximum for
species in this country is a little over a hundred pairs, and the short and broad pill mil-
lipede Glomeris marginata only has 19 pairs. The technical name Diplopoda refers to
the fact that most segments appear to have two pairs of legs. This arises from the fu-
sion of pairs of segments as an adaptation to a burrowing way of life. These diplo-seg-
ments are linked by elaborate ball-and-socket joints which allow for flexibility of the
body as a whole while preventing the telescoping of segments during the low-geared
thrusting power of the numerous legs. The legs spend more time on the ground pro-
pelling than off the ground, and the ability to push is characteristic of the Diplopoda.
The most familiar millipedes are the cylindrical black species up to five centi-
metres long with 30-60 rings. When moving freely on the surface, their short legs
move in a series of six or seven waves down the length of the body. At rest, they
commonly roll into a plane or helical spiral, depending on the species, and display a
fringe of projecting legs. Many species also curl up when disturbed but some freeze
like players in musical statues while the snake millipede Ophiulus pilosus thrashes
violently from side to side. These millipedes of the families Julidae and Blaniulidae
comprise about half the British species, and a much higher proportion of individuals
found actually in the soil.
Four species, including the common pill millipede Glomeris marginata ( Fig.
27 ) , are able to roll up into a perfect ball with all their limbs concealed. In this state
G. marginata may easily be mistaken for the pill woodlouse Armadillidium vulgare
mentioned earlier. It is common in calcareous districts both in grassland and wood-
land. Feeding studies with this species indicate that only 6-7 per cent of the ingested
material is assimilated; its main contribution to the soil economy is, therefore, in the
physical comminution of leaf litter and dead grass which is thus rendered more sus-
ceptible to microbial attack.