Modification of legs

Legs :- One pair of legs is located on each of the segments. Legs are important organs of mobility. A typical leg consists of six segment ; the subcoxa is constituted by the pleurites and not a distinct segment; the coxa is the base; the trochanter articulates with the coxa but is fixed with the next segment; the femur is the largest part of the leg; the tibia is only a slender shaft; the tarsus is divided into 2-5 segments and the terminal pretarsus. The tarsus often has pad-like plantulae or pulvilli.

Different segments of the legs are modified in various insect groups, depending upon the mode of life, their habits and the speed of their movement.

Various modifications of legs:-

Saltatorial type- Saltatorial type of legs are found in the grasshopper, Poekilocerus pictus. In this case, the femur is greatly enlarged and init consists strong muscles. Tibia is elongated and is spined dorsally; when it strikes against the ground surface the inner takes a leap in the air.

Raptorial type- Raptorial t ype of legs are the modified fore-legs in the super family Mantoidea. These legs re adapted for catching and holding the prey in between the greatly enlarged and ventrally grooved femur and the blade like curved tibia. The forelegs in the other Embioptera are adapted for web spinning. The metatarsus of foreleg is swollen to accommodate the silk gland, out of which comes the silk thread.

Notatorial types of legs:- The notatorial legs are typical of the giant water bug, Belostoma indica. These legs are flattended and are marginally fringed with dense hair, forming oar-like structures.

Ambulatorial or running type:- Ambulatorial or running type of legs are typical of the cockroach, Periplaneta Americana. The legs are cylimdrical, with well developed coxae and well defined tarsomeres.

Scooping type:- The scooping type of legs are found among dragonflies (sub-order Anisopetra): the legs are long having rows of stiff bristles along the inner margins.

Grasping type:- In the grasping type of legs, found in male giant diving beetle. Dytiscus marginalis, the basal tarsomeres are enlarged, forming circular disc-bearing suction cups on the inner surface. The bladder-footed legs are the characteristic feature of the order Thysanoptera, the common example being the onion thrips, Thrips tabaci ; in these legs the distal tarsomeres bear vesicle to provide a firm hold on to the surface on which the insects feed.

Fossorial type:- Fossorial legs are adapted for digging into the ground and are typically represented as the forelegs of the male cricket, Gryllotalpa spp. In this case, the tibia and tarsi are flattened and are shaped like shovels for digging the soil.

Clinging type:- The clinging type of legs are found in the human louse, Pediculus humanus; here a padded projection in present at the distal end of tibia and the pre tarsus is modified into an enlarged claw-shaped structure which fits on the pad. The forelegs of honeybee, Apis spp. are adapted for antennae-cleaning by a tibial spur which overlaps the bristled notch. The middle pair of legs in honeybees are modified for pollen brushing; there are transverse rows of bristles on the inner side of metatarsi, which are used for brushing the heap. The pollen-collecting legs are also found in honeybees; these are the hind legs in which tibia are modified to form cavities (pollen baskets), fringed with spines on the outer surface, and a concave pollen cavity fringed with spines at the proximal end of metatarsus.