THE SOIL FAUNA: ANTHROPODS - The Soil - page 78

of imported plants. They are said to be synanthropic since they are associated with
human habitation and do not seem to colonize rural habitats. Perhaps they can simply
cope better than the native fauna with the exotic diet produced by imported trees and
shrubs.
CENTIPEDES
Centipedes may be thought of as the predatory counterparts of millipedes. They feed
mainly on small insects, mites, spiders, nematodes and other centipedes. Some ve-
getable matter is consumed and one species Haplophilus subterraneus is known to
turn vegetarian at times, and cause damage to root crops. The most characteristic and
unique feature of the group is the pair of large, inward curving poison claws borne
on the modified first pair of limbs under the head. These can clearly be seen with the
naked eye when looked at from below. Lithobius pilicornis can inflict a painful bite to
humans, while the large, tropical Scolopendra centipedes, which frequently measure
15 cm in length and more than a centimetre across the body, can partly immobilize
small mammals with their poison.
Apart from a few small relatives of this tropical genus, there are two main groups
of centipedes in Britain: those living mainly on the soil surface and those living un-
derground. The somewhat forbidding names Lithiobio-morpha and Geophilomorpha
merely mean stone-living forms and soil-loving forms. The lithobiid centipedes are
relatively broad animals with 15 pairs of long, powerful legs adapted for fast moving.
Large specimens may reach 30-35mm in length and span 15mm across the extended
legs. Although all centipedes lack the calcareous and waxy exoskeleton of millipedes,
and are therefore liable to desiccation, they undoubtedly roam widely at night in
search of prey while seeking refuge under stones and in litter during the day.
The Geophilomorpha are less often noticed but are the largest group with 23
species (plus two or three more currently being described). They are recognized by
their very elongated serpentine body and curious flickering movement of the antennae
when in motion ( Plate 7 ) . Most species are between 20 and 60mm long when adult,
and bear 37 to 101 pairs of short legs - much as in millipedes. They are red, brown or
pale yellow in colour, and some species are phosphorescent particularly in the autumn
and when disturbed. They have no eyes but are able to perceive light through their
thin leathery skin.
Their most striking feature is their enormous flexibility which is achieved by
subdivision of each segment into two - the opposite anatomical condition to that seen
in millipedes. With the extra joints, an animal can turn back on itself by the flexing
of three adjacent segments, a facility which allows it to explore narrow crevices and
interstices in the soil. For reversing out of blind alleys that are too narrow even for
this, the rearmost pair of legs are adapted to feel the way like a pair of posterior an-