Cockroach

https://youtu.be/rFruVNQfF30

Classification

• Kingdom – Animalia
• Phylum – Arthropoda
• Class – Insecta
• Order – Blattodea
• Family – Blattidae
• Genus – Periplaneta, Blatta
• Species – more than 4500 species of cockroaches

General points

• Habitat – warm, dark and damp places like kitchens, storehouses and sewers.
• Body size – length 0.6 cm – 7.6 cm; Periplaneta americana – 3.4 cm – 5.3 cm.
• Body shape – dorsoventrally flattened.
• Body colour – usually brown or black; some species have a yellow, red or green body colour.
• Body symmetry – bilateral symmetry.
• Habit – nocturnal, i.e. active and feeding at night.
• Exoskeleton – made up of hard chitinous plates called sclerites.
• Nutrition – omnivores/scavengers; some species of cockroaches show cannibalism.
• The most common species of cockroaches are Periplaneta americana (American cockroach) and Blatta orientalis (Oriental cockroach).
• Cockroaches are considered serious pests and are vectors for several diseases.

Morphology

The body is divided into three distinct regions – head, thorax and abdomen.

Head

• Triangular in shape.
• Made up of 6 chitinous plates called cephalic sclerites in the embryo.
• In adults, the cephalic sclerites are fused to form a single head capsule.
• I cephalic sclerite – Occiput
  Present at the top of the head and made up of 2 parts called epicranial plates, joined at the epicranial suture.
• II cephalic sclerite – Frons
  Present below the occiput on the anterior part of the head.
• III cephalic sclerite – Clypeus
  Present just below the frons on the anterior part.
• IV cephalic sclerite – Post-occiput
  Present below the occiput on the posterior part of the head.
• V cephalic sclerite – Gena
  Present on the lateral side.
• VI cephalic sclerite – Post-gena
  Present inner to the gena.
• The head also bears the mouthparts and several sense organs.

Mouth

• The mouth faces downwards; this is called a hypognathous mouth.
• The mouthparts are of the biting and chewing type.
• They are made up of several parts – labrum, mandibles, maxillae, hypopharynx and labium.
• Labrum – also known as the upper lip, which hangs from the clypeus.
• Mandibles – a pair of mandibles is present inner to the labrum, with grinding and incising regions for cutting the food.
• Maxillae – a pair of maxillae is present beneath the mandibles. They help in the mastication of food and in cleaning the antennae, and each bears a maxillary palp with olfactory receptors.
• Hypopharynx – a median, flexible lobe that acts as the tongue, lying within the cavity enclosed by the mouthparts.
• Labium – also known as the lower lip, formed by the fusion of two parts. A pair of labial palps also arises from the labium and bears sensory bristles.

Sense organs

Antennae

• Paired.
• Multi-segmented; each segment is called a podomere.
• Long and filiform (thread-like).
• Arise from the antennal sockets.
• Bear tactile, thermal and olfactory receptors to monitor the surroundings.

Compound eyes

• Paired.
• Black in colour.
• Bean-shaped (kidney-shaped).
• Placed dorsolaterally on the head.
• Each is made up of about 2000 units called ommatidia.
• Produce mosaic vision.

Ocelli/fenestrae

• Round and pale.
• Present inner and upper to each antennal socket.
• Vestigial simple eyes.

Thorax

• Divided into 3 segments:
  • Prothorax
  • Mesothorax
  • Metathorax
• Each thoracic segment is made up of 4 chitinous sclerites – a dorsal tergum, 2 lateral pleura and a ventral sternum.
• The tergum of the prothorax, called the pronotum, is extended to protect the neck and is the largest of the thoracic terga.
• Each thoracic segment bears a pair of legs, called prothoracic legs, mesothoracic legs and metathoracic legs, arising from the prothorax, mesothorax and metathorax respectively.
• Two pairs of wings, called the forewings and hindwings, arise from the mesothorax and metathorax respectively.
• Forewings/mesothoracic wings – thick, leathery and dark in colour. They are not used for flight, but they protect and cover the hindwings.
• Hindwings/metathoracic wings – thin, transparent, delicate and broad. They are used for flight.

Abdomen

• Made up of 11 segments in the embryo, but reduced to 10 segments in adults.
• The abdomen is broader than the thorax and is dorsoventrally flattened.
• A typical abdominal segment consists of a dorsal tergum, 2 lateral pleura and a ventral sternum, but the 10th segment lacks a sternum.
• In males, the 7th tergum covers the 8th tergum, but all 9 sterna are visible.
• In females, the 7th tergum covers the 8th and 9th terga, and the 7th sternum covers the 8th and 9th sterna.
• Anal cerci – long, thick structures arising from the 10th tergum, which bear tactile receptors and phonoreceptors. Present in both males and females.
• Anal styles – thin, small outgrowths arising from the 9th sternum, which bear tactile receptors. Anal styles are present only in males and are absent in females.