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Insect leg
1.
2. Insect leg consists of six segments
They are: 1. basal coxa (coxae) which
articulates with the thorax
at the pleuron region
2. Small trochanter
3. Femur (Femora)
4. Tibia (Tibiae)
5. Segmented tarsus (tarsi)
6. Pretarsus
3.
4. The coxa has smaller anterior region and a larger posterior
region called the meron
The articulation is brought about by ball and socket joint
It may be monocondylic that allows rotatory movement or
dicondylic that permits only back and forth movement
The trochanter articulates with the coxa but usually forms an
immovable attachment with the femur
The next two segments called the femur and tibia are typically
the longest
5. The tarsus which is derived from a single segment is usually
divided into individual tarsomeres
The number of tarsomeres varies from three to five and it is
often used as a taxonomic tool
The basal segment is often larger than others and called the
basitarsus
The structures distal to the tarsus are collectively called the
pretarsus
The pretarsus consist of a single claws or a pair of claws and one
or more pads called the pulvillus (Pulvilli), bulbous lobe like
arolium or empodium or bristles
6.
7. Although an insects legs are locomotory in function, they are extensively
modified to perform varied functions
Both the immature and the adults have thoracic legs
However, there are apodous (lacking legs) larvae (fly maggots) and adults
(female scale insects, Homoptera)
There are different kinds of legs they are
1. Ambulatorial (Walking leg)
2. Cursorial (Walking and Running leg)
3. Fossorial (Digging or Burrowing leg)
4. Raptorial (Predatory or Grasping leg)
5. Saltatorial (Leaping and Jumping leg)
6. Natatorial (Swimming leg)
7. Scansorial (Climbing or Clinging leg)
8. CURSORIAL (Walking and Running)
Typically developed inset legs with long femur and tibia that are well
adapted for walking and running eg: Cockroach
9.
10. The forelegs are modified for grabbing and holding the prey
It is common in predatory insects eg: Praying Mantids
Their forelegs are prehensile and suited for prey capturing and are of little
use in locomotion
The long and mobile coxa facilitates an extended reach to capture the prey
Raptorial legs are also used to hold the female during mating eg: Dytiscus,
Coleoptera.
11. NATATORIAL (Swimming leg)
The legs of several aquatic insects are modified to facilitate swimming
eg: aquatic bugs(Hemiptera) and adult predaceous diving beetles. Their femur,
tibia and first four tarsomeres are broad and flat with marginal setae and together
function as oars
12.
13. Apart from the modifications associated with the locomotory
functions, in Protura the legs are articulated in an elevated position,
anterior to the body and the legs are probably Sensory in function
Many insects also use their legs to groom parts of the body to
remove detritus particles for instance, the assassin bugs, the
neuropterans and the dipterans in the act of grooming hold the
antennae between their forelegs
The mosquitoes have a comb consisting of several rows of
setae at the distal end of the foretibia
14. The combs in the act of scrapping run along the proboscis or
antennae in rapid stroke Schistocerca has cleaning groove
between the first and second pads of the tarsomeres
The legs of many insect bears various structure eg: The hind
tibiae the honey bees bear pollen basket or Corbiculum which
is engaged in the gathering of pollen from the flowers they
visit.
Rows of stiff spines on the inner side of hind basitarsus serve
as a pollen comb that collects pollen from the midlegs and
abdomen.
A row stout bristles at the distal end of tibia and a small plate
fringed with hairs at the basal end of basitarsus collectively
called the pollen packer that stores the pollen the corbiculum
15. The pollen in the corbiculum is transported to the hive
Exactly same quantity pollen by weight are arranged between
the combs to maintain balance in flight
The foreleg of males of some species of diving beetles bear
large suction discs on the tarsi which are used for grasping the
female during copulation
The spiny ad closely placed legs of dragonflies and damsleflies
are held together as a basket to scoop the prey during flight
Their legs are not useful in locomotion
16.
17. The tarsal and pretarsal segments are also distinctly modified
For example, the pad – like pulvillus is found on the lower surface of
each tarsal segment
Some insect have a bulbous, lobe like structure, the empodium, which
arise from the end part of the unguitractor plate and also is located
between the claws eg. Robber fly
Varied degree of reduction of legs occurs in some insects
For instance, in some butterflies the anterior tarsi are reduced or the
forelegs are nonfunctional
The hind femora of certain species of short – horned grasshoppers
have short, peg – like structures with which they rub the forewings
and produce a sound
The long – horned grasshoppers and crickets possess oval auditory
organs or tympana at the base of each foretibia
18.
19. • Reduction in the legs is often associated with the sedentary or some other
specialized habits such as burrowing
• Some species like the bagworms are totally spodous and they live in
bags constructed by the larvae
• Parasitic female strpsipterans do not have legs
