Fundamentals of Entomology

Types of legs

• Insects are six legged arthropods and hence the class is also called Hexapoda. In insects legs perform varied functions and are modified accordingly.
  1. Digging or Fossorial type: The forelegs are greatly expanded, tibia is digitate with three segmented tarsus beneath. The legs are used for digging soil. E.g. Mole cricket
  2. Jumping or Saltatorial type: The hindlegs are modified for leaping or jumping. Femur is greatly enlarged, tibia is very long e.g. Grasshopper
  3. Walking or running type: All three pairs of legs are equal in size and comparatively long. Trochanter is two segmented. E.g. Cockroach
  4. Grasping or Raptorial type: The forelegs are modified for catching prey. The coxae are elongate and moveable, the femora are spiny and grooved along the lower side, the tibiae are also spiny and fit into the groove along the femur. The prey is held between the femur and tibia. Tarsus is five segmented. E.g. Preying mantids.
  5. Swimming or Natatorial type: Usually the hind legs are modified for swimming. Hind coxae are flat and fixed to the body. Numerous long stiff hairs are present on the lateral aspects of the tibia and tarsus. E.g. diving beetles.
  6. Pollen carrying type: The hind legs of honey bees are modified for carrying pollen. At the junction of tibia and basitarsus, a cavity guarded by hairs is present which is used for carrying pollen. This structure is also called carbiculum. E.g. Worker honeybee.
  7. Antenna cleaner: the forelegs of honey bees are modified for cleaning antenna. The first segment of tarsus has a notch, which can be closed by the flat tibial spur. The notch has an inner lining of fine hairs. The antenna is placed in the notch, closed by the spur and then drawn out to clean. E.g. Worker honeybees
  8. clinging type: The legs are strong and adapted for maintaining a strong and firm hold on the host. Tarsi are single segmented and terminate in a single sickle shaped claw which works against a tibial process. E.g. Head louse and body louse.
  9. Climbing type: The terminal segment of the leg, pretarsus, bears two claws and beneath the claws are two lobes ccalled pulvulii. Between the pulvulii is an elongate spine called empodium. The empodium and pulvulii help the insect to climb smooth surfaces. E.g. housefly.