🪳 Cockroach – Morphology and Anatomy

The common Indian cockroach (Periplaneta americana) belongs to Phylum Arthropoda and Class Insecta. It is a nocturnal, omnivorous insect usually found in warm, damp and dark places (kitchens, drains, basements). It has a tough outer covering called an exoskeleton made of chitin, which protects the body and prevents water loss.

🌿 1️⃣ Morphology (External Features)

✅ Key Points (Quick NEET View)

  • Body is elongated, dorso-ventrally flattened (flat from top to bottom) → helps it hide in narrow spaces.
  • Size: usually 3–4 cm long (adult).
  • Colour: reddish-brown.
  • Body divided into Head, Thorax, Abdomen.
  • Body wall has hard plates called sclerites joined by soft membranes → allows flexibility.

Head (Sensory + Feeding)

  • Head is triangular and lies at right angle to the body.
  • Bears:
  • 1 pair long antennae → touch + smell (sensory)
  • 1 pair compound eyes → vision (detect movement)
  • Mouthparts of biting and chewing type (important NEET line)
🔸 Mouthparts (Biting–Chewing)
Mouthpart Easy meaning Function
Labrum upper lip covers mouth opening
Mandibles (pair) strong jaws cutting + crushing food
Maxillae (pair) holding tools hold and manipulate food
Labium lower lip holds food, forms floor of mouth
Hypopharynx tongue-like mixes saliva, helps swallowing

Thorax (Locomotion + Wings)

  • Thorax has 3 segments:
  1. Prothorax (first) – has a large shield-like plate called pronotum.
  2. Mesothorax
  3. Metathorax

✅ Each thoracic segment bears one pair of legs → total 3 pairs of walking legs.

🔸 Wings (2 pairs)
  • Forewings (tegmina): leathery, protective (not main for flight)
  • Hindwings: thin, membranous → used for flight

Abdomen (Segments + Reproductive Features)

  • Abdomen has 10 segments.
  • In females, some posterior segments are less visible externally because of enlarged plates, but the abdomen is considered 10-segmented.
  • At the end of abdomen:
  • Anal cerci (pair) in both male & female → sensory (detect vibrations)
  • Anal styles (pair) only in male → an easy NEET identifier

🧠 2️⃣ Anatomy (Internal Systems)

(a) Digestive System

The alimentary canal is divided into foregut, midgut, hindgut.

🔸 Foregut (Storage + Grinding)
  • Mouth → pharynx → oesophagus → crop → gizzard
  • Crop stores food temporarily.
  • Gizzard has chitinous plates → grinds food.
🔸 Midgut (Digestion + Absorption)
  • Midgut secretes digestive enzymes.
  • Has 6–8 hepatic (gastric) caeca opening into it → increases digestive area and enzyme secretion.
🔸 Hindgut (Water Absorption)
  • Ileum → colon → rectum → anus
  • Rectum absorbs water; rectal pads help reabsorb water and salts.

(b) Circulatory System (Open Type)

  • Open circulatory system → blood (haemolymph) flows in body cavities called sinuses (haemocoel), not in capillaries.
  • Heart is a long tube on dorsal side with 13 chambers and openings called ostia.
  • Haemolymph has no respiratory pigment because oxygen is carried directly by tracheae (not by blood).

(c) Respiratory System (Tracheal System)

  • Cockroach breathes using a tracheal system.
  • 10 pairs of spiracles (stigmata) open on the body:
  • 2 pairs on thorax
  • 8 pairs on abdomen
  • Spiracles lead to tracheae → tracheoles, which directly deliver oxygen to tissues.
  • Therefore, respiration is independent of blood.

(d) Excretory System (Malpighian Tubules)

  • Excretion is by Malpighian tubules (many thin yellow tubules) opening at the junction of midgut and hindgut.
  • Main excretory product: uric acid → hence cockroach is uricotelic.
  • Advantage: uric acid needs very little water → helps survival on land.

(e) Nervous System

  • Consists of:
  • Brain (supra-oesophageal ganglion)
  • Sub-oesophageal ganglion
  • Double ventral nerve cord with segmental ganglia
  • Controls movement, sensory functions (antennae/eyes), and reflexes.

(f) Reproductive System (Ootheca = Very Important)

Male:

  • Testes in 4th–6th abdominal segments
  • Vas deferens → ejaculatory duct → male gonopore
  • Accessory glands form seminal fluid

Female:

  • Ovaries in 2nd–6th abdominal segments
  • Oviducts → vagina → genital chamber
  • Female forms a protective egg case called ootheca.
  • Each ootheca contains 16 fertilized eggs (arranged in two rows).

🧬 3️⃣ Economic Importance

  • Cockroaches are household pests.
  • They contaminate food and can act as carriers of pathogens causing food poisoning, diarrhoea, dysentery.
  • Their shed body parts can trigger allergy/asthma in some people.
  • They also serve as food for lizards, frogs, birds and help in decomposition in nature.

💡 Questions and Answers

Q1. What is the function of Malpighian tubules in cockroach?

A1.

Malpighian tubules are the excretory organs. They remove nitrogenous wastes mainly as uric acid and also help in osmoregulation (maintaining water and salt balance). They open into the gut, so waste leaves the body along with faeces.

Q2. How many oothecae does a female cockroach produce in her lifetime?

A2.

A female cockroach can produce about 15–40 oothecae in her lifetime (this number can vary with conditions). Each ootheca has 16 eggs, so one female can give rise to many young ones.

Q3. Name the segments bearing wings in cockroach.

A3.

Wings arise from the mesothorax (forewings/tegmina) and metathorax (hindwings).

Q4. Why does cockroach blood not carry oxygen?

A4.

Because cockroach has a tracheal system. Oxygen enters through spiracles and travels via tracheae and tracheoles directly to tissues. So haemolymph does not need respiratory pigments like haemoglobin.

Q5. Why is uric acid excretion helpful for cockroach?

A5.

Uric acid is a semi-solid waste and needs very little water for removal. This helps cockroach conserve water and survive in dry conditions.

💡 Short Questions and Answers

Q1. Why is cockroach called an arthropod?
A1. Cockroach belongs to Arthropoda because it has jointed legs (arthro = joint, poda = legs) and a chitinous exoskeleton.

Q2. What does dorso-ventrally flattened mean and why is it useful?
A2. It means the body is flattened from top (dorsal) to bottom (ventral). This helps cockroach hide in cracks and narrow spaces, which protects it from predators.

Q3. What is the difference between tegmina and hindwings?
A3. Tegmina (forewings) are thick and leathery, mainly protective. Hindwings are thin and membranous and are mainly used for flight.

Q4. Why is the mouthpart of cockroach called biting and chewing type?
A4. Because the mandibles cut and crush food, and other mouthparts hold and move food for chewing. This suits its omnivorous feeding habit.

Q5. What is the function of the crop and gizzard?
A5. The crop stores food temporarily, while the gizzard grinds food using hard chitinous plates so digestion becomes easier.

Q6. Why is cockroach circulation called open?
A6. Because blood (haemolymph) is not confined to a network of capillaries. It flows in sinuses (haemocoel) and bathes organs directly.

Q7. How does respiration occur in cockroach?
A7. Air enters through spiracles, passes into tracheae, then into tiny tracheoles, and finally oxygen diffuses directly into body tissues.

Q8. What is an ootheca and why is it important?
A8. An ootheca is a hard protective egg case formed by the female. It protects eggs from drying and damage. Each ootheca contains 16 eggs.

Q9. Mention one feature to identify a male cockroach externally.
A9. Male cockroach has anal styles (present only in males) on the 9th abdominal segment.

Q10. Why is cockroach called uricotelic?
A10. Because it excretes nitrogenous waste mainly as uric acid, using Malpighian tubules.