Geoscience Reference
In-Depth Information
of 20-28mm and often attracts attention through its habit of wandering about garden
paths and even into houses. When disturbed, it adopts a characteristic threatening pos-
ture by opening its mandibles wide and erecting the end of its body. This suggests
both an ability to give a powerful bite, which it can, and an ability to sting, which it
cannot. It is, in fact, preparing to discharge a strong unpleasant odour, from vesicles
at its rear end, which has a repellent effect on natural enemies. Its English name is
thought to derive from a medieval legend, but its origin seems to be lost in the mists
of time.
Two other related families, the Pselaphidae and Scydmaenidae, must rank among
the smallest beetle predators. Between one and two millimetres in length, many of
them are known to feed on mites, especially the oribatid or beetle mites described
earlier. The Scydmaenidae have scimitar-like mandibles with which they grasp and
hold their prey while piercing their tough shells. External digestion appears to take
place through the action of digestive enzymes secreted into their prey as in the case
of spiders (Some Pselaphidae are ant commensals as described later).
The dominant beetle predators belong to the family Carabidae known as ground
beetles, though the German name Laufkäfer, which means running beetles, is perhaps
a more apt description. They are placed with water-beetles in a separate sub-order
from other beetles, the Adephaga, a Greek word meaning ravenous feeders. The genus
Carabus
itself includes some of our largest British beetles, weighing up to 600-700
mg. They offer ideal subjects for studying insect anatomy for every segment of legs,
mouthparts and antennae can be clearly seen with the naked eye. Different species
show a wide range of elytral sculpturing and colouring, from the violet-tinted, fine
matt finish of
Carabus violaceus
to the coarsely ridge-and-furrowed metallic green of
Carabus nitens
, and the tuberculate, dark copper or burnished black of
Carabus gran-
ulatus
(
Fig. 29
): the nineteenth century French naturalist Jean Henri Fabre described
this last species as having “a cuirass magnificent with the refulgency of copper pyrites
and ornamented with alternate pins and bosses”.
