Geoscience Reference
In-Depth Information
rest of the year is spent underground. Weevil larvae are soft, plump grubs with curved
and legless bodies befiting their sedentary way of life.
Species of
Trachyphloeus
are perhaps the best examples of ground weevils for
both adults and larvae live at the roots of low-growing plants. They are often cryptic-
ally coloured in greys and duns, and covered with encrustations which render them
very inconspicuous. Another weevil,
Barypeithes pellucidus
, was the most common
species of beetle caught in pitfall traps in a wide-ranging survey of London gardens.
This was unexpected for, usually, it is the active, predatory species that stumble into
such traps. It is not known to be harmful but is thought to be associated with shrubs
and young trees and must, therefore, be viewed with some suspicion.
The larvae of chafer and scarab beetles are rather like overgrown weevil grubs
with small legs and a swollen abdomen. The cockchafer and its close relatives are
known as May or June bugs and are familiar for their habit of flying to lights at night.
The larvae used to be serious pests of grassland in this country but have declined in
significance as the amount of permanent pasture has decreased so markedly since the
1950s; short-term ley grassland is no use as the larvae need four years to mature. The
adults constituted a very important food item for horse-shoe bats whose numbers have
declined seriously in recent years.
Wireworms became a serious pest during and after the war because of the
ploughing up of old pasture. Species of
Agriotes, Limonius
and
Athous
, in particular,
could occur at high densities of the order of 2-3 million an acre, around 600 a square
metre, especially on heavy loam and clay soils. They too have a four or five year lar-
val life and when the pasture was ploughed up they turned their attentions,
faut de
mieux
perhaps, to the potatoes, cereals, onions and other crops that were planted sub-
sequently, causing damage for several successive years.
The adults of these slim, elongated larvae are known as click-beetles or skipjacks
on account of the way they fall to the ground when disturbed and then leap into the
air with a loud click to right themselves - and startle would-be predators. A.D Imms
gives a detailed account of this behaviour and its significance in his topic on Insect
Natural History in this series.
B
EETLES AS PREDATORS
The largest family of soil and ground-living beetles are the rove beetles or Staphyl-
inidae, instantly recognizable by their waistcoat-like elytra which leave the last six
segments of the abdomen exposed. They are mostly small, black and insignificant -
definitely a group for specialists - feeding mainly on fungi, spores, soil algae, carri-
on and decaying vegetable matter. Many species, however, are carnivorous, and the
best known of these is the devil's coach horse
Staphylinus olens.
It reaches a length
