Legs

 

Most insects have three pairs of walking legs — one pair on each thoracic segment. Each leg contains five structural components (segments) that articulate with one another by means of hinge joints:

1. Coxa
2. Trochanter
3. Femur
4. Tibia
5. Tarsus

The term pretarsus refers to the terminal segment of the tarsus and any other structures attached to it, including:

• • ungues — a pair of claws
  • arolium — a lobe or adhesive pad between the claws
  • empodium — a large bristle (or lobe) between the claws
  • pulvilli — a pair of adhesive pads

Leg Adaptations and Modifications

Thoracic legs are often adapted for special functions. Their structure may provide clues to other aspects of an insect’s biology.  Five common leg modifications are illustrated below:

• Saltatorial — jumping
• Raptorial — seizing
• Fossorial — digging
• Natatorial — swimming
• Cursorial — running

Abdominal Prolegs

Some insect larvae, such as caterpillars, have pairs of short fleshy legs on one or more abdominal segments.  These legs may have tiny hooks or barbs (called crochets) that serve to grip the substrate.  Abdominal prolegs never occur in an insect’s adult stage.  They are a unique larval adaptation derived from a completely different embryological origin than the thoracic legs.