Order: Dictyoptera (‘net-winged’)
Characteristics:
Generally two pairs of wings, although these
may be reduced or even absent; forewings have
well developed veins and tend to be hardened,
they overlap down the mid-dorsal line;
membranous hindwings are folded below
forewings; long whip-like, many-segmented
antennae; omnivorous, with mouth parts
adapted for biting; tarsi, 5-segmented;
incomplete metamorphosis, with egg and
nymph stages.
Family: Blattidae
Species characteristics:
Oriental Cockroach (Blatta orientalis)
Adults, 20-24mm long; colour, dark-brown,
nearly black; wings of male cover two-thirds of
abdomen, wings of female are vestigial; can
climb rough but not smooth vertical surfaces.
German Cockroach (Blattella germanica)
Adult, 10-15mm long; colour, yellowish-brown
with two longitudinal dark marks on pronotum;
wings well developed in both sexes; can readily
climb rough and polished vertical surfaces.
American Cockroach (Periplaneta americana)
Adult, 28-44mm long; colour, red-brown with
yellow border around pronotum; no yellow
submarginal stripes on forewings; last segment
of cerci, twice as long as wide.
Australian Cockroach (Periplaneta australasiae)
Adult, 30-35mm long; colour, light brown with
ivory-yellow circular band enclosing large,
distinct, bilobed black spot; yellow submarginal
stripe at base of forewings.
Nymphs:
The nymphs of all species are similar in
appearance to the adult but smaller.
Immediately after hatching or moulting the
nymphs are white, but the cuticle soon darkens
to the normal colour.
Distribution
Cockroaches are common in commercial
premises associated with the production or
handling of food. Also in public buildings and
domestic premises eg apartment blocks.
Gregarious and nocturnal, they spend the day
hiding in cracks and crevices around such areas
as sinks, drains, cookers, the backs of cupboards
and in refrigerator motor compartments. They
especially favour buildings with service ducts
and complex plumbing installations.
Infestations may be introduced as egg cases or
adults in incoming laundry, on raw materials, in
crates and packaging, or arise as the insects
enter buildings via such routes as drains or
refuse chutes.
B. orientalis and B. germanica are the most
common species in Northern Europe. They are
occasionally found together, but B. germanica
generally prefers warmer, humid environments,
e.g. centrally heated buildings, whilst
B. orientalis is frequently encountered in cooler,
less humid areas such as basements and drains.
P. americana and P. australasiae are tropical and
sub-tropical species but are also found in ports
and shipping areas in temperate climates.
Significance
Cockroaches are potential vectors of diseases
such as dysentery, gastroenteritis, typhoid and
poliomyelitis. Their diet is omnivorous and
includes fermenting substances, soiled septic
dressings, hair, leather, parchment, wallpaper,
faeces and food for human consumption. The
latter may be contaminated either by the
mechanical transfer of causative agents of
disease from the insect’s body, or by
transmission in the faeces. An outbreak of food
poisoning in a Brussels hospital subsided
immediately an infestation of B. germanica was
controlled.
Cockroaches and their faeces may cause allergic
reactions especially amongst sensitive
individuals eg asthmatics. Exposure may result
from ingestion or through the inhalation of
materials derived from cockroaches in airborne
dust. In addition, food may be tainted with the
characteristic smell of the cockroach, which is
produced by faeces and salivary/abdominal
gland secretions, or by the dead insects.
