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Ground Beetles-Carabidae are agile and long-legged. These
ground beetles are usually seen scurrying along the ground
at remarkable speeds in search of prey. The ground beetles all have lustrous
bodies, and some are brightly colored. This makes them so popular with
collectors that several species are in serious danger of extinction: examples
are Carabus olympiae and C. solieri.
Most of the 25,000 species of Carabidae ground beetles are active at night. Some cannot fly.
They are distinguished by their somewhat flattened bodies and by the rows of
fore-and-aftridges and furrows that mark their stiff wing covers.
Most ground beetles prefer temperate or even cold climate; only a few species
are found in the tropics. The Carabidae are most commonly found living under
stones and logs, in gravel along watercourses, and among fallen leaves and other
dead vegetation at the bases of trees. Some species, however, live deep in the
bowels of the earth, in topsoil, and in caves. Ground beetles of the genus
Calosoma are frequently found in trees, and some species live under snow. In the
Himalayas, ground beetles have been seen at altitudes of more than 15,000 feet.
Most of the Carabidae are formidable predators, hunting their prey in water, on
land, and in trees. Although they feed primarily on arthropods, worms, and
mollusks, ground beetles are not squeamish about how they satisfy their
voracious appetites, and will prey on a wide variety of animals.
Because of their fierce appetites, ground beetles have been a valuable aid to
man in the control of destructive insects. They are sometimes imported into a
region to rid it of pests. The ground beetles themselves are rarely destructive.
The notable exceptions are members of the genus Zabrus that frequently damage
cereal crops.
Carabidae larvae generally live out in the open. A larva can be
recognized by its elongated shape, depressed cranium, sharp mandibles, and in
most cases, by a pair of bristle like appendages at the end of the abdomen. The
diet and habits of the Carabidae larvae usually resemble those of the adults.
The pupae form in tiny underground cells, built by adults with secretions from
their Malpighian tubes.
Corobus. Ground beetles of the genus Cora bus, most
often found in cool, damp mountain valleys, are notable in that many of them are
unable to fly. Their wings may be rudimentary or entirely atrophied. This
distinction has made the Carabus an excellent walker, but has also led to the
isolation of Carabus populations and the establishment of a large number of
species and local races. Today, more than 1,000 species and geographical races
of Carabus are known.
Members of the genus Carabus feed primarily on snails and slugs, but they also
hunt various insects and worms. They are nocturnal and, even in the larval
stage, are completely at home in aquatic environments, where they hunt mollusks.
Cychrus. The genus Cychrus is
another group of efficient and highly specialized mollusk hunters; found in damp
forest environments, they are equipped with a highly flexible head and thorax,
enabling them to dig snails from their shells.
Cofosomo. Carabidae of the genus
Calosoma, found in forest regions, are marked by their ability to climb trees.
One species, C. sycophanta, has proved highly beneficial to man. Preying on such
defoliating insects as Tortrix mridana, the cockchafers, and the larvae of
Lymantria dispar, the processionary caterpillar, this brilliantly-colored,
tree-climbing ground beetle has saved forests of trees, especially the
vulnerable deciduous oak, from devastation.
The adult C. sycophanta spends the winter in a tiny underground cell; in the
spring, when the sun has warmed the ground sufficiently, it emerges among the
mosses and fallen leaves, armed with a tremendous hunger. At this time of the
year the larvae of many defoliating insects are in full activity, and C.
sycophanta has only to climb the nearest tree to discover a veritable feast. One
of the prime victims of this ruthless beetle is the hairy processionary
caterpillar (the Lymantria larva). Processionary caterpillars usually move in a
regimented fashion; the species found in pines move in single file and those
found in oaks form double ranks. C. sycophanta hurls itself upon these
defenseless files like a wolf attacking a flock of sheep.
The adult C. sycophanta hunts for about 50 days; then it retires to an
underground cell where it rests until the following spring, when the feast
begins again. By this time it has eaten the equivalent of 200 to 400 large
Lymantria larvae. The females have already gone down and laid their eggs in a
niche in the ground. The average female lays about 100 eggs, but some lay as
many as 500.
C. sycophanta's war on defoliating insects does not stop when the adults retire
for the winter. Just before the adults go underground, the young are hatched and
quickly take to the trees. Here they feed on caterpillars, chrysalids and even
sluggish Lymantria adults. Day and night they march, surprising their victims
and ripping them open with their sharp mandibles. Some seek out the nests of the
processionary caterpillars and move in as unwanted guests. The young have been
shown to be even more bloodthirsty than their parents, often killing more than
they can eat. After about two weeks of slaughter, the C. sycophanta larvae, each
having killed about 40 large victims, leave the trees and bury themselves in the
ground, where they become pupae. They remain underground during the winter and
emerge as adults in the spring.
Commonly found from western Europe to Siberia, C. sycophanta was first
introduced in the United States, primarily in New England, in the early years of
the 20th century. Many forests in the eastern United States had suffered severe
damage due to the accidental importation of Lymantria dispar and Euproctis
chrysorrhoea (like L. dispar, the larvae of this species, the browntail moth,
feed on foliage). In spite of the massive introduction of C. sycophanta,
however, little progress has been made in keeping the populations of these moths
under control.
C. sycophanta is commonly called the fiery searcher, perhaps because it
sometimes gives off large amounts of a blistering juice. A member of the same
genus that is native to North America is Colosoma scrutator. It is almost as
large as C. sycophanta,
Harpalus. Like C. sycophanta, most
species of Carabidae are carnivorous. Some, however, such as the members of the
genus Harpalus, are predominantly vegetarians. Members of Harpalus attack
flowers, fruit, and the green parts of herbaceous plants, and are therefore a
menace to agriculture.
These are small- to medium-sized beetles. Their colors may be green, blue, or
black. The black color is usually lusterless and is often characteristic of the
females, which are larger than the males. Members of Harpalus are usually found
in gardens; during the daylight hours they hide under stones and bricks
bordering flower beds.
Brachmus. Among the most
interesting of all insects are bombardier beetles belonging to the genus
Brachinus. Not markedly different in appearance from other Carabidae, they are
set apart by a remarkable system of self defense. When attacked, the bombardier
beetle ejects a drop of volatile fluid, from the anal glands at the end of its
abdomen, into a special stiffened sac.
The sac contains other secretions, and when the fluids are mixed there is an
audible explosion like the sound of a tiny balloon bursting. The explosion
results in a tiny puff of caustic gas-a smoke screen behind which the bombardier
beetle makes its retreat. This gas is so caustic that it can even burn human
skin. It is therefore extremely effective in discouraging attackers. And, as the
bombardier beetles are quite social little animals, when one member of a group
is attacked, a reaction is triggered: the air is often filled with a series of
small explosions.
Although they are the most dramatic, bombardier beetles are not the only
Carabidae that defend themselves by emitting secretions. Members of the genus
Aptinus also eject fluids with an explosive force.
Mormolyce phyllodes, a flat, leaf
like ground beetle from Java, is one of the few carabids that live in tropical
climates. It is said to eject a secretion that can paralyze the human hand for
24 hours.
In addition, this tropical ground beetle displays other remarkable
characteristics. The adults, more than two inches in length, have an
extraordinary flattened appearance -hence the name phyllodes, meaning "like a
leaf. This appearance is caused by blade like extensions from the wrinkled wing
covers that enclose the thorax and abdomen.
Members of Mormolyce phyllodes feed on fungi growing on dead trees deep in
equatorial forests. The females lay their eggs in the fungi, where the larvae
tunnel in. For food, the larvae wait for animals to wander by, and then attack
ferociously. If two tunneling larvae should meet, however, they will attack each
other without hesitation. According to many specialists, this strange species is
on its way to extinction.
Trechus. Ground beetles of the
genus Trechus are notable for their ability to survive in an enormous variety of
environments. They have been found inhabiting Pacific islands as well as the
Arctic and Antarctic regions. They also hold the altitude record for Coleoptera.
Some have been found high on the slopes of Mount Kenya and at altitudes above
15,000 feet in the Himalayas. Some species of Trechus dwell in caves and are
blind; they are found primarily in the Alps, the eastern Carpathians, and the
Pyrenees.
Omophron. The members of this genus have curiously
shaped, compact bodies. They live along sandy shores near the water's edge.
Notiophilus. The broad-skulled
beetles of this genus are confined to dry, sunny habitats in spite of the fact
that the term Notiophilus means "fond of dampness."
The Subfamily Scaritinae. These
carabids build complicated burrows along sandy shores. The scarites are unusual
in that they alternate between a daytime existence in underground burrows and a
nocturnal existence prowling above ground.
The Subfamily Bembidiini is
represented in most parts of the world. Most of these tiny ground beetles live
in damp or even aquatic environments, attacking insects that spend the critical
phases of their metamorphoses in water. However, one genus, the blind Anillus,
lives underground, mostly under rocks half buried in the soil of wooded
hillsides.
The Subfamily Pterostichini is an
enormous group, consisting of some 5,000 species. One genus, Molops, is found in
cool, damp environments, usually in forests or mountains.
Laemosthenes. The elongated beetles
of this genus tend to inhabit wooded areas, rock piles, and caves. Their
ancestors lived in the Mediterranean basin; it is thought that they originated
in the southern Aegean area during the Miocene epoch more than 12 million years
ago.
Amara. Carabidae of the genus Amara are distributed
over much of the Northern Hemisphere, and prefer to live in areas exposed to the
sun. They feed on herbaceous plants and often prey on small animals. Many
species of Amara are colored green, turquoise, bronze, or black; they can be
recognized easily by their boat-shaped, flattened bodies. They are often seen
scurrying among rocks and tufts of grass or climbing the stalks of plants.
Chlaenius. The brightly colored
Chlaenius, with their brilliant metallic luster, live in marshes or at the edge
of mountain streams;
some members of this genus inhabit the banks of brackish lagoons. One notable
exception is the small, brilliantly colored Callistus lunatus, which avoids
humidity whenever possible, preferring to live in very dry, sheltered
environments.
Lebia. One member of this genus, a
flat beetle known as Lebia scapularis, is extremely beneficial to man. It preys
on another coleopteran, the elm leaf beetle (Galerucella luteola), which, as its
name suggests, feeds on the foliage of elm trees and can cause serious damage.
L. scapularis gorges itself on the eggs and larvae of the elm leaf beetle,
thereby keeping a dangerous defoliator in check.
Another species that lives throughout the eastern United States and southern
Canada is L. grandis. It can be found under logs and stones.
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