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Cockroach: Morphology of Head, Thorax and Abdomen, Practice Problems and FAQs

How do you react when you see a cockroach? Most of us would either scream out of fear or be disgusted at their sight. Have you ever tried to know why cockroaches are so resilient? Which group of living organisms do they belong to? 

Cockroaches belong to the class Insecta of phylum Arthropoda. What do cockroaches usually look like? The ones that we commonly see have a brown or black body, right? Did you know that in tropical regions, bright yellow, red and green colored cockroaches are also found? 

cockroaches

Cockroaches are omnivores who would pretty much eat anything and everything and they mostly come out during the night as they are nocturnal beings. You will mostly find them in dirty and damp places. You will be amazed to know that there are around 4500 species of cockroaches that inhabit Earth. Thankfully for us, only 30 of those are adapted to live around humans.

Some of the common species of cockroaches are Periplaneta americana (American cockroach), Blattella germanica (German cockroach), Blatta orientalis (Oriental cockroach).

Let us discuss more about the morphology of a cockroach.

General Morphological Features

Have you ever paid attention to the body of a cockroach? They have a body that is 0.6 cm to 7.6 cm long. The body consists of segments that are divided into three regions - head, thorax and abdomen. 

It is usually covered by a brown coloured chitinous exoskeleton which is present in the form of hardened plates, known as sclerites, on either side of the segments. The dorsal sclerites are known as tergites and the ventral ones are known as sternites. The sclerites are joined to each other with the help of a thin and flexible membrane known as the arthrodial membrane. 

cockroach

Head of Cockroach

The head of the cockroach is triangular in shape and shows movement in all directions due to the presence of a flexible neck. Different types of mouthparts are present in the head that are directed downwards. The head is positioned at a right angle to the long axis of the body.

Head of the cockroach

The exoskeleton of the head is composed of six fused segments known as sclerites or plates. These segments include two epicranial plates, two gena, one frons and one clypeus.

sclerites in cockroach

The head of a cockroach also contains sensory parts. These are the specialised sense organs that help the cockroach in vision and touch. Different types of sensory organs present in cockroaches are compound eyes, antennae and fenestrae.

Compound Eyes

One pair of compound eyes are present on the top of the head. Each compound eye possesses units known as ommatidia. They help in vision.

Antennae

A pair of antennae is present in cockroaches. These arise from membranous sockets lying in front of eyes. Each antenna is made up of segments called podomeres. They are tactile in function and help to detect food and other objects. 

Fenestrae

Fenestrae represent underdeveloped, simple eyes. They are present on the upper side of the antennal socket. They are small, rounded, pale coloured areas. They are sensitive to light. 

sensory parts

Mouth

The cockroach takes solid food therefore, the mouth parts are of biting and chewing type. The mouth of a cockroach has different parts. These are the labrum, mandibles, maxilla, labium and hypopharynx or tongue. 

Labrum is the upper lip that holds food particles during feeding. There are two mandibles present in cockroaches that help in the grinding of food. Maxilla are also two in number that are associated with maxillary palps. They hold the food and give it to the mandibles for the process of mastication. Maxilla are used for cleaning the antennae and first pair of legs. Labium is considered as a lower lip that has labial palps. Hypopharynx lies in the cavity that is enclosed by the mouthparts. Hypopharynx is flexible and directs saliva towards food.

mouth parts of cockroach

Thorax of Cockroach

 Thorax is divided into three segments as follows:

  • Prothorax (anterior)
  • Mesothorax (middle)
  • Metathorax (posterior)

Head is connected with the thorax with the help of the neck, which is an extension of the prothorax. The sclerite of the prothorax is large and is known as a pronotum.

segments of thorax

Two pairs of wings are present on the dorsal side - a pair of forewings and another pair of hindwings. 

Forewings, also known as tegmina or elytra, are the anterior pair of wings which arise from the mesothorax. They are opaque, dark and leathery. They have no role in flight. They are protective in function and cover hindwings when the cockroach is at rest. 

Hindwings are the posterior pair of wings. They arise from the metathorax. They are transparent and membranous and help in flight.

wings of cockroach

Thorax also has six legs that are present on the ventral side. The three pairs of legs are classified as:

  • Prothoracic legs - Arise from prothorax.
  • Mesothoracic legs - Arise from mesothorax.
  • Metathoracic legs - Arise from metathorax.

legs of cockroach

Each leg consists of five segments:

  • Coxa - Stout and flattened basal part articulated with the thorax
  • Trochanter - Small and irregular part articulated with the coxa and femur
  • Femur - Long, narrow and toughest part with bristles
  • Tibia - Thin, slender and longest part with bristles
  • Tarsus - Lowest part with five segments called tarsomeres

parts of  cockroach legs

The last tarsomere has claws called tarsal claws. Tarsal claws have arolium which help in adhesion. Tarsomeres have bristles. 

segments of tarsus

Abdomen of Cockroach

Ten abdominal segments are present in both males and females but abdomen in females is broader compared to that of males. The embryo has 11 segments. Each abdominal segment possesses four sclerites - a dorsal tergum, a ventral sternum and two lateral pleura. It is broader in females than that in males.

comparison of male and female abdomen

The genital pouch or chamber in male cockroaches lies at the posterior end of the abdomen and is surrounded by the 9th and 10th terga on the dorsal side and the 9th sternum on the ventral side. It contains the dorsal anus, ventral male genital pore which is an opening of the ejaculatory duct and gonapophysis that represent the male external genitalia. 

Genital pouch in males

The genital pouch in females is also known as a brood pouch and is bound by the boat-shaped 7th sterna along with the 8th, and 9th sterna. It contains -

  • a gonopore which is a genital pore.
  • spermathecal pores that are multiple inconspicuous minute pores.
  • collateral glands which are two highly branched tubular glands.

Genital pouch in females

Abdominal appendages are the external body parts on the abdomen. They are anal cerci and anal style. Anal cerci are a filamentous sensory structures. They are present in the 10th segment. Anal style is a pair of short, unjointed leg-like structure that helps in copulation. Males have anal styles whereas, females do not.

Abdominal appendages

The arthrodial membrane between the fifth and sixth abdominal terga is depressed to form a stink gland. It produces the secretions with the characteristic foul smell. In the cockroach, 

ten pairs of spiracles are present. First pair is present between the prothorax and mesothorax. Second pair is present between the mesothorax and metathorax. Eight pairs are present in the abdominal region. Spiracles are also called stigmata. They are slit-like apertures on the lateral side of the body. They possess bristles and valves. They are connected with the respiratory tubes called tracheae

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Practice Problems of Cockroach

Ques:- Which of the following is correctly matched?

A. Ommatidia - functional units of eyes in cockroaches
B. Podomeres - segments of tarsus 
C. Pronotum - sclerite of mesothorax
D. Hypopharynx - upper lip

Solution: One pair of compound eyes are present on the top of the head of a cockroach. Each compound eye possesses functional units known as ommatidia. The ommatidia help the cockroach in vision. 

Podomeres are the segments of the antennae. Segments of the tarsus are tarsomeres.

Pronotum is the sclerite of the prothorax.

Labrum is the upper lip and the hypopharynx is the tongue in the mouth of the cockroach.

Hence, the correct option is a.

Ques:- Study the diagram and choose the correct option.

cockroach

A. 1 - prothoracic leg, 2 - metathoracic leg, 3 - mesothoracic leg
B. 1 - mesothoracic leg, 2 - prothoracic leg, 3 - metathoracic leg
C. 1 - metathoracic leg, 2 - prothoracic leg, 3 - mesothoracic leg
D. 1 - prothoracic leg, 2 - mesothoracic leg, 3 - metathoracic leg

Solution: In the given figure, ‘2’ represents the prothoracic leg, ‘1’ represents the mesothoracic leg and ‘3’ represents the metathoracic leg. Prothoracic legs arise from prothorax, mesothoracic legs arise from mesothorax and metathoracic legs arise from metathorax.

Thus, the correct option is b.

Ques:- Which of the following statement(s) is/are true?

A. Abdomen is broader in female cockroaches
B. Male cockroaches have anal cerci but females do not.
C. The male genital pouch is formed by the 7th, 8th and 9th abdominal segments.
D. There are eight pairs of spiracles in cockroaches.

Solution: In female cockroaches, abdomen is broader than males. Both males and females have ten segments in the abdomen. 

Anal cerci is present in both male and female cockroaches. Anal style is present only in males.

The female genital pouch is formed by the 7th, 8th and 9th abdominal segments.

There are ten pairs of spiracles in cockroaches.

Hence, the correct option is a.

Frequently Asked Questions of Cockroach

Ques:- Which sensory organs are present in the cockroaches?

Answer: In cockroaches, three sensory organs are present in the head region. These are compound eyes, antennae and fenestrae. Compound eyes are present in a pair at the top of the head. They help in vision. Antennae are present in a pair and are tactile in function. They help the cockroaches to detect food and other objects. Fenestrae are simple eyes that are sensitive to light.

Ques:- Name the different mouthparts of the cockroach along with their role.

Answer: The mouth of a cockroach has different parts. These are the labrum, mandibles, maxilla, labium and hypopharynx or tongue. 

  • Labrum is the upper lip that holds food particles during feeding. 
  • There are two mandibles present in cockroaches that help in the grinding of food. 
  • Maxilla are also two in number that are associated with maxillary palps. They hold the food and give it to madibles for the process of mastication. Maxilla are used for cleaning the antennae and first pair of legs. 
  • Labium is considered as a lower lip that has labial palps. 
  • Hypopharynx lies in the cavity that is enclosed by the mouthparts. Hypopharynx is flexible and directs saliva towards food.

Ques:- How many wings does a cockroach have?.

Answer: Two pairs of wings are present on the dorsal side - a pair of forewings and another pair of hindwings. Forewings are the anterior pair of wings which arise from the mesothorax. They are opaque, dark and leathery. They have no role in flight. They are protective in function and cover hindwings when the cockroach is at rest. 

Hindwings are the posterior pair of wings. They arise from the metathorax. They are transparent and membranous and help in flight.

Ques:- What are stink glands in cockroaches?

Answer: The arthrodial membrane between the fifth and sixth abdominal terga is depressed to form a stink gland. It produces secretions with a characteristic foul smell. 

Ques:- Which is the morphological feature through which one can distinguish between male and female cockroaches?

Answer: Anal style is the distinguishing feature of male and female cockroaches. Anal style is a pair of short, unjointed leg-like structures. Males and females can be distinguished externally through anal style. Males have anal styles whereas, females do not have anal styles.

Related Topics to Morphology of Cockroach in Biology

NCERT Class 11 Biology Chapters 

The Living World Biological Classification Plant Kingdom
Animal Kingdom Morphology of Flowering Plants Anatomy of Flowering Plants
Structural Organization in Animals Cells: The Unit of Life Biomolecules
Cell Cycle and Division Transport in Plants Mineral Nutrition
Photosynthesis in Higher Plants Respiration in Plants Plant Growth and Development
Digestion and Absorption Breathing and Exchange of Gases Body Fluids and Circulation
Excretory Products and their Elimination Locomotion and Movement Neural Control and Coordination
Chemical Coordination and Integration

 

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