BLATTIDAE - Cockroaches sketches


Blattidae is an insect family that includes cockroaches. They are found all over the world and are distinguished by their flattened bodies, long antennae, and broad, shield-like pronotum.

There are over 4,600 species of cockroaches known, with approximately 450 of them belonging to the Blattidae family. These species are typically large, ranging in length from 20 to 100 mm, and are brown or black in colour. They have two pairs of wings, with the front pair toughened and leathery and the back pair membranous.

Cockroaches are shield-shaped insects with stout horny plates covering both the dorsal and ventral surfaces of the thorax and abdomen. When viewed from above by the rim of the prothorax, the head is tucked under and hidden, with two large compound eyes placed well in front; in some groups, there are also two ocelli; the antennae springing from below the eyes are very long and slender, composed of a large number of short ringed segments. The jaws are well adapted to their vegetarian habits, though some domestic species are almost omnivorous in their tastes. Their legs are long and stout, covered with spines, and the legs of species that live under stones and logs are usually thickened. Many species have two pairs of stout membranous wings, with the front pair (elytra) thickened, opaque, and coarsely veined, while the hind wings, though frequently small, are fan-shaped, membranous, and well adapted for flight.

The cockroach is one of the oldest insects, and roaches can be found in fossil beds in both Europe and America, many of which are related to our current forms.

Cockroaches are considered pests because they can be found in human dwellings and can cause food contamination, allergic reactions, and the transmission of disease-causing organisms.

The female has an odd habit of carrying her keeled egg capsule protruding from her abdomen for some time before depositing it in a suitable situation.

A number of cosmopolitan species may be classified as domestic insects because they are only found around houses or human haunts; in London, Blatta orientalis is commonly referred to as the “back beetle,” which is swarming in cellars and kitchens.

The large yellow roach that comes flying around the room to the light in Sydney is Periplaneta americana, an introduction from America that has almost driven the smaller indigenous Periplaneta Australasiae out of our houses; whereas in some southern and eastern states of America, our Australian roach has been introduced and has become the common domestic pest. The German Roach, also known as “The Croten Bug of America”, Phyllodromia qermanica, is occasionally found near Sydney wharves. Many of these bush and house roaches have glands at the tip of their abdomen from which they can emit a foetid odour as a form of defence when disturbed. Cockroaches are a large and diverse family. Most of our common native forms are wingless and live under rotten logs or stones; some of the largest species can be found in the dry interior.

Saussure described several of our species (Mem. Soc. Geneve 1863-4-9): Walker many others (Brit. Mus. Catalogue Blattidae 1868): and Tepper has been a consistent worker at this group in South Australia for several years; descriptions of most of his species can be found in the Transactions of the Royal Society of South Australia between 1893-95, and the Zoology of the Horn Expedition 1896.

Panesthia laevicollis is common in forests, where it can be found burrowing in damp rotting logs. It is a wingless black insect measuring nearly 1 1/2 inches in length, with the thorax narrow and flattened above the head, which has comparatively short antennae; the legs short but very spiny; and the dorsal surface of the abdomen covered with irregular punctures.

Periplaneta Australasiae is a wingless, dull yellow species that is broadly marked with black on the thorax segments and finely barred with the same colour on the upper edges of the abdominal segments. It is about 11/4 inch long and can be found from South Australia to the central parts of Western Australia.

Polyzosteria limbata is a large dark brown cockroach with yellow margins on the outer edge of the dorsal plates; it is common in the Sydney area, and can often be seen resting on stumps and fences in the Botany area; it, like several other species, has the habit of discharging a most offensive liquid when disturbed. Polyzosteria pubescens is a related but much larger insect that can grow to be 2 inches long and 1 1/2 inches wide. It has a uniform dull brown tint and is common around Kalgoorlie, Western Australia, and will most likely be found throughout the interior.

Polijzosteria mitchellii is a variegated, dull inetallic green cockroach that ranges across the same country but is no longer than 1 1/2 inches long. The upper surface is yellow-margined around the edges, and the legs and undersurface are mottled.

Our giant cockroach, Geoscapheus giganteus, is 2 1/2 inches long and 1 1/2 inches across the middle of the body. It, like the previous three, lacks wings, with the large prothoracic shield overlapping the head. It is bright reddish brown in colour, crenulated, and very rugose in the centre of the dorsal surface. Saussure described another large roach under the name Macropanesthia rhinoceros in the same year (1895) that Tepper obtained this fine species, forming a new genus for its reception and adding a second species that he named M. muelleri.