THE SOIL FAUNA: ANTHROPODS - The Soil - page 84

siderable damage to cereal crops, root vegetables, strawberries and hops, but they are
readily controlled with insecticides these days.
The other main pest species are the night-feeding noctuid larvae, known as cut-
worms from their habit of biting through the stems of plants at or just below soil level.
They include the turnip moth Agrotis segetum , garden dart Euoxa nigricans and large
yellow underwing Noctua pronuba , all of them voracious and impartial feeders on
young plants. They can do a lot of damage to seedlings of lettuce, beet, carrots and
onions and even young trees in nurseries.
About a quarter of the British insect fauna belongs to the order Diptera which
includes flies and midges - as many as the beetles and moths put together. There are
at least thirty families whose larvae commonly occur in the soil, and they are often
quite abundant. In general, however, they have tended to be the Cinderellas of the soil
fauna in terms of the attention paid them because of the difficulty of extracting them
efficiently and identifying them. Several fungus-gnats and moth-flies live in loose soil
and litter throughout their adult stages as well. Some scuttle-flies have gone still fur-
ther in their commitment to an earth-bound way of life through the atrophy of wings
so that they can only hop and scuttle among dead leaves and decaying vegetation.
There are three main groups of Diptera which can be distinguished in the larval
as well as the adult stages. The most primitive suborder contains the midges, gnats,
March flies and crane flies. The larvae of these are usually long cylindrical creatures
with a complete head capsule and mandibles that move in a horizontal plane. The
second group includes soldier flies, robber flies, horse flies, long-headed flies and a
few other families. The larvae are also elongate with distinct, if incomplete, head cap-
sules and sickle-shaped mandibles. They, like the adults, are largely predaceous. A
great diversity of larvae are represented in the third, most advanced, group of flies, but
they all have a vestigial head-capsule and hook-like mandibles which can sometimes
be seen through the skin. Many of these are soft, plump maggots, essentially like the
'gentles' used by anglers as bait. Others, occurring in various kinds of decaying ve-
getable matter, have conspicuous spines or are strongly flattened and tough-skinned.
The most bizarre form is the rat-tailed maggot of the drone fly Eristalis tenax whose
telescopic siphon enables it to breathe air while remaining submerged in semi-liquid,
anaerobic mud or dung.
As usual, most attention has been paid to pest species. The large bulb fly Mero-
don equestris and lesser bulb flies Eumerus species belong to the same hoverfly fam-
ily as the drone fly. Their larvae attack Narcissus and other similar bulbs making them
go rotten. As with so many pests, they become a problem only where the food plant is
grown consistently in an area in monoculture, as enormous populations of the insects
are then able to develop in a few generations.