The cockroach (Periplaneta americana) is an arthropod belonging to the class Insecta, order Blattodea, and phylum Arthropoda. It is a nocturnal omnivore found in warm, humid environments.
General Features of Cockroach
- Scientific Name: Periplaneta americana
- Kingdom: Animalia
- Phylum: Arthropoda
- Class: Insecta
- Order: Blattodea
- Size: 3-7.5 cm long
- Color: Reddish-brown
- Habitat: Dark, moist places such as kitchens, basements, drains
- Diet: Omnivorous, feeds on food waste, paper, clothes
- Reproduction: Sexual reproduction with internal fertilization
External Morphology of Cockroach
Segments of Cockroach
The body is bilaterally symmetrical, segmented, and dorsoventrally flattened. It is divided into three regions:
- Head (Small, triangular)
- Thorax (Three segments)
- Abdomen (Ten segments)
1. Head of Cockroach
- Formed by the fusion of six segments.
- Triangular in shape, bent downward at an angle (hypognathous).
- Bears:
- A pair of compound eyes (Faceted, enables mosaic vision).
- Antennae (Long, filamentous, sensory).
- Mouthparts (Chewing and biting type).
2. Mouthparts of Cockroach
Cockroach has “chewing and biting” type mouthparts consisting of:
- Labrum (Upper lip, immovable, protects mouth)
- Mandibles (Two strong, chitinous structures for cutting & chewing)
- Maxillae (Pair of appendages, holds food, taste receptors)
- Labium (Lower lip, assists in manipulation of food)
- Hypopharynx (Tongue-like structure, assists in swallowing)
3. Thorax of Cockroach
Divided into three segments:
- Prothorax (First pair of legs attached)
- Mesothorax (Second pair of legs + First pair of wings)
- Metathorax (Third pair of legs + Second pair of wings)
- Legs: 3 pairs, jointed, adapted for running (cursorial locomotion).
- Wings:
- Forewings (Tegmina): Hard, protective, leathery.
- Hindwings: Soft, membranous, used for flight.
4. Abdomen of Cockroach
- Composed of 10 segments.
- In males, the 9th and 10th segments bear anal styles (absent in females).
- Both sexes have cerci, sensory appendages on the 10th segment.
Internal Anatomy of Cockroach
1. Digestive System of Cockroach
The digestive system is divided into three parts:
(i) Foregut (Stomodaeum)
- Mouth → Pharynx → Esophagus (carries food to crop).
- Crop: Large sac-like structure, stores food.
- Gizzard (Proventriculus):
- Thick-walled, chitinous.
- Grinds food using chitinous teeth.
(ii) Midgut (Mesenteron)
- Hepatic caecae (Gastric caecae): Secrete digestive enzymes.
- Midgut: Digestion and absorption of nutrients occur here.
(iii) Hindgut (Proctodaeum)
- Ileum → Colon → Rectum → Anus
- Water is reabsorbed in the rectum, and waste is eliminated.
2. Respiratory System of Cockroach
- Direct respiration via a tracheal system (no blood involvement).
- Spiracles (10 pairs, openings on the body).
- Trachea → Tracheoles → Tissues (O2 enters, CO2 exits).
- Air sacs: Store air for flight.
3. Circulatory System of Cockroach
- Open circulatory system (no blood vessels, hemolymph directly bathes organs).
- Heart:
- 13-chambered, tubular heart.
- Located dorsally.
- Blood flows posterior to anterior.
- Hemolymph: Colorless, contains plasma + hemocytes (no hemoglobin).
4. Excretory System of Cockroach
- Malpighian tubules: Main excretory organs, remove nitrogenous waste (uric acid → uricotelic).
- Fat bodies, nephrocytes, urecose glands also aid excretion.
5. Nervous System of Cockroach
- Ganglionated nervous system.
- Brain: Small, controls vision & antennae.
- Ventral nerve cord: Chain of segmental ganglia.
- Suboesophageal ganglion: Controls mouthparts.
6. Sensory Structures
- Antennae (touch & smell).
- Compound eyes (mosaic vision, nocturnal adaptation).
- Cerci (detect air movements & danger).
Reproductive System of Cockroach
Male Reproductive System
- Testes: Located in 4th-6th abdominal segments.
- Vasa deferentia: Carries sperm.
- Seminal vesicle: Stores sperm.
- Male gonopore: Ejaculation.
- Phallic gland: Secretes spermatophore (sperm packet).
Female Reproductive System
- Ovaries: Located in 2nd-6th abdominal segments.
- Oviducts: Carry eggs to genital chamber.
- Spermatheca: Stores sperm.
- Ootheca: Egg case (16 eggs inside).
Comparison Table: Male vs Female Cockroach
| Feature | Male Cockroach | Female Cockroach |
|---|---|---|
| Size | Smaller | Larger |
| Anal Styles | Present | Absent |
| Spermatophore Formation | Present | Absent |
| Ootheca Formation | Absent | Present |
Fertilization & Development
- Internal fertilization.
- Oviparous reproduction (egg-laying).
- Ootheca (egg case) deposited in humid places.
- Nymphs emerge after 6-8 weeks and undergo gradual metamorphosis before becoming adults.
This note comprehensively covers the morphology, anatomy, and reproduction of cockroaches in detailed yet exam-oriented form.
