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Cockroaches (Order: Blattodea)

A photograph of the Tawny Cockroach (_Ectobius pallidus_)

The Tawny Cockroach (Ectobius pallidus) is one of three cockroach species native to Great Britain.
© http://www.entomart.be/

Introduction

Cockroaches first evolved around 350-300 million years ago and are probably one of the most despised of all insects. For some people the mere mention of cockroaches will send them running for cover. However, there are roughly 4,500 described species of cockroaches and only about 25 are considered to be pests. The rest of the order are extremely beneficial insects in a variety of ecosystems.

However, when you mention the name cockroach, most people will think of the relatively small number of species that infest homes and other dwellings. Cockroaches seek out warm places and often enter homes or business premises. In these sheltered areas they breed and populations can become very large indeed.

Main characteristics of Cockroaches

Most species of cockroach are omnivorous (that is, they'll eat almost anything from plants, dead animals and even glue) and are predominantly found in tropical and sub-tropical regions.

Adult cockroaches are small to large insects (3 - 90mm in length) and usually have a broad flattened body. The pronotum (a shield-like structure on the top of the thorax behind the head) often overhangs the body on either side and covers the head.

Not all species have wings but, when these are present, the fore wings are thick and leathery and the hind wings are thin and fan-like.

Life-history

In most species of cockroach the female produces a hardened egg case called an ootheca. Commonly this is carried by the female and, in some species, the ootheca may be carried inside the abdomen and not visible. The ootheca can contain 10-50 eggs depending on the species. Cockroaches undergo incomplete metamorphosis with nymphs looking like small versions of the adults. In the winged species, the wings appear at the final moult.

Most species of cockroach have little to do with their young once they hatch from the oothecae. However, some species show a significant amount of parental care. In some species, the nymphs are carried on the back (underneath the wings) of the female cockroach and the nymphs feed on liquid secretions from pores on her back and even by piercing the membrane between her abdominal plates and feeding on the haemolymph (insect blood) coming from the wound.

In some species, and warm conditions, adulthood is reached within 40 days but in colder climates this can take over a year. However, many cockroach species are reasonably long lived and commonly kept pet species, like Madagascan Hissing Cockroaches, may live for up to three years.

A photograph of the American Cockroach (_Periplaneta americana_)

The American Cockroach (Periplaneta americana) is a common pest species found in the home. Photograph by Gary Alpert, used under GFDL

Classification

At one time the cockroaches were considered to be part of the Order: Orthoptera (Grasshoppers and Crickets) but have since been classified as a separate Order called Blattodea.

The Blattodea contains seven families but some of the most well known are the pest species (found in the family: Blattidae) such as Periplaneta americana (the American Cockroach) and Periplaneta germanica (the German Cockroach).

Perhaps one of the most interesting aspects of cockroach classification is that of Termites now being thought of as a family of eusocial (living together in a colony with only some individuals being able to reproduce) cockroaches. Termites were previously thought to be a separate order (Isoptera) of their own.

How to find them

Pest cockroaches can be commonly found in poorly kept food storage facilities, restaurants and blocks of flats. Within Great Britain there are only three native species of cockroach and these have a scattered and local distribution in southern England. The three native species are never pests.

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