COCKROACH (Periplaneta americana)

The common species of cockroach in the tropics is Periplaneta americana. This is most active at night, during day it hides in dark places and crevices of walls.



Kingdom : Animalia

Phylum : Arthropoda

Class : Insecta

Order : Dictyoptera

Family : Blattidae

Genus : Periplaneta

Species : americana

Characteristics of order: Dictyoptera

  • The mouth parts are of the biting type
  • presence of broad membranous outer wings
  • long and thread-like antennae
  • possession of the anal cerci
  • presence of long and tough tegmina
  • Metamorphosis is incomplete.


Cockroaches live in dark, dirty and dump warm places e.g. pipes that carry sewage. During day they live in crevices of walls, cupboards, underneath drawers and in boxes.They are active at night thus referred to as nocturnal.

Adaptation of a cockroach to its environment

  • Cockroaches have dorso-ventrally flattened bodies to fit in narrow places.
  • Its body is dark brown to camouflage well against a dark background.
  • They are smooth and greasy to escape easily from predators.
  • It has one pair of long antennae for feeling and smelling the area around their body.
  • The shape and disposition of the legs enables swift running in confined spaces where flight is impossible.
  • Since they are omnivorous, they survive on a wide variety of food materials.
  • Their nocturnal emergence renders them less liable to capture.
  • Sensitivity of anal cerci to air, movements in crevices ensures a considerable measure of safety for the eggs, with this further protection of the tough oothecal coat.
  • They have spines on their legs for defence.

NB:Other insects belonging to the order Dictyoptera include locusts, crickets, praying mantis and grass hoppers etc.

External features:

  • The adult cockroach is about 4cm long.
  • It is dorsal-ventrally flattened body with brown colour.
  • It has a hard thick exoskeleton made of chitin.
  • The body is made up of three main divisions, each segment of thorax and abdomen consists of dorsalplate tegmen (plu:-terga) a ventral plate, sternum (plu-sterna) and two internal plates, pleura.

Dorsal view

dosal view

The head

  • The head is small and pear-shaped.
  • It bears a large kidney-shaped pair of compound eyes.
  • In front of each compound eye lies a longthread-like segmented antennae (feelers). These are sensitive to touch, smell and vibrations.
  • The head has biting and chewing mouth parts –mandibles for cutting and crushing food, maxillary palps for holding food, a labrum (upper lip) and labium (lower lip).
  • The head is connected to the thorax by short neck.
mouth of cockroach

The thorax

  • The thorax consists of three segments: the prothorax, the mesothorax and the metathorax.
  • Each of the segments bears a pair of jointed legs on its ventral surface. They end in a pair of sharp claws with a soft hairy pad, the arolium (plural: arolia) between them
  • The prothorax is the largest of the thoracic segment
  • The paired wings are attached to dorsal surface of mesothorax and metathorax.
  • The anterior (fore) wings are narrow, brown leathery and still and are called elytra or tegmina. They are not used for flight but for covering and protection of broad, membranous posterior (hind) wings when at rest.
hing leg

The abdomen

This is made up of 10 segments. Only seven are easily seen because tergum of seventh segment lovers 8thand 9thsegmentThe flat, broad tergum of the 10thsegment bears a pair of jointed sensory structures, the cerci in males, another additional pair of short structures styles.There are 10 pairs of oval openings called spiracles at the side of the body, 2 on thorax and 8 in abdominal segment

Identification of a cockroach’s sex

In males, there is a pair of slender stylesthat are used to hold and manipulate the female during copulation.In females, there is a pair of boat shaped structures called the podical platesused for holding eggs.

male female cockroach

The life cycle of a cockroach

A cock roach undergoes incomplete metamorphosis.After mating, the fertilized eggs are stored in an egg-case called ootheca.This is hard, chitinous structure 1cm long containing eggs in rows of eightThe female carries ootheca for a number of days before depositing them in dark obscure places. Within a week, it turns dark brown.After six weeks, the eggs hatch out intoyoung, wingless and colorless cockroaches called nymphs. After 2 weeks they turn brown like adult but wingless.The nymph grows and undergoes ecdysis, about 7 times and every two ecdysis, the nymphs are called instars. After the last ecdysis, the nymph becomes adult cockroach which has a life span of about 2 months.

Economic importance of cockroaches

  • They destroy clothes, books, shoes, furniture and spoil food.
  • They spread disease causing germs such as cholera, dysentery etc. especially those in latrines
  • They contaminate food if not properly covered.
  • They dirten places with their faeces as they move around especially when many.
  • They are food to some organisms like birds.
  • They are used in biological studies as specimens.

Control of cockroaches

  • Improve personal and public hygiene.
  • Use of environmentally friendly insecticides like doom, etc.
  • Use of biological control methods.
  • Polish the walls of the house to close the small crevices.