2. Insects - 3 major body regions: head, thorax, and abdomen .
Head - 5 to 7 fused segments (bears the eyes, antennae, and mouthparts).
Thorax - three segments (pro-, meso-, and metathorax).
Each of these segments - bears one pair of legs.
If wings are present - found on the meso- and metathorax only.
Appendages used for movement are also attached to the thorax.
The top of the prothorax is called the pronotum.
Abdomen - 11 or fewer segments that generally do not bear any appendages (except for
segments near the rear which may have appendages associated with reproduction).
OVERALL BODY PLAN
3. Typical insect: 3 pairs of legs (Segmented type)
Position - Ventral surface of the thoracic segment
(Pro-, meso-, and metathoracic regions)
Function :Primary organs of walking and running, but
according to the habit and habitat, they are
modified for various purposes.
Each leg contains- 5 segments
i) Coxa
ii) Trochanter
iii) Femur
iv) Tibia
v) Tarsus
Pretarsus- typically represented by complex set of claws.
TYPICAL INSECT LEG
4. i) Coxa: First or proximal or basal leg segment. It is freely movable and attached to the thoracic
segment.
ii) Trochanter: Second segement, small and single segmented
except dragonfly and damselfly – 2 segmented (called Trochantelus)
articulates with Coxa but usually attached to Femur.
iii) Femur: Largest or stoutest and most powerful part of the leg
Closely attached to Trochanter
iv) Tibia: Long and slender part of the leg.
Downward projecting spines are present (Func- Climbing and Footing).
v) Tarsus: 5th segment
sub segmented- 2-5 segments called Tarsomeres
Pretarsus: 6th or last segment, pair of terminal curved structures claws (ungues).
Lobe-like or adhesive pad structure in between the claws called
Arolium. Pair of adhesive pads- pulvilli.
Large bristle or lobe b/w claws- Empodium
SEGMENTS OF TYPICAL LEG
5. MODIFICATIONS OF LEG
i) Saltatorial -- jumping ii) Raptorial -- seizing iii) Fossorial -- digging
iv)Natatorial -- swimming v) Cursorial – running
While the legs are normally adapted for walking many insects have them modified
for variety of functions.
They are:
i) Saltatorial/jumping
Hind legs adapted for jumping.
i) Work well for jumping because they (enlarged
legs filled with bulky, strong muscles).
iii) jump, propelling forward very long distances
very quickly.
These legs are characterized by an elongated
femur and tibia.
The femur is greatly enlarged giving articulation
for large muscles of tibia which are used in jumping and leaping.
Eg: Grasshoppers, crickets and katydids (order Orthoptera).
6. Raptorial legs/Seizing type
: Modified for grasping (catching prey).
• Modified from Saltatorial legs
Eg: Mantids (order Mantodea), ambush bugs, giant water bugs and water
scorpions (order Hemiptera).
• hunting legs, the kinds of legs you see on predatory insects.
• these legs are usually at the front of the insect and are used to grab and hold
prey while they eat.
• Coxa of foreleg is more elongated whereas the trochanter is small. Tibia is
spinous and fits along the femur.
7. • Swiftly moving insects such as roaches and tiger beetles.
• Cursorial legs tend to be long and narrow and are designed so that the insect
can move very quickly.
• Things with this type of leg are often hard to catch – or hard to step on if
you’re dealing with roaches
Eg: Ants,wasps, Cockroach etc.
Cursorial/Running type:
• differentiated by the tarsus which is comparatively longer and touches the
ground while running.
• Similar to walking legs.
8. Ambulatory/ walking type
Similar to cursorial type.
Femur and tibia are long. Legs are well developed similar in form.
Eg:cockroach, leaf beetles.
Natatorial (Swimming leg):
e.g. Hind legs of water bug or water Beetle,
Femur, tibia and first four tarsomeres are all broad
and flattened.
Their edges are provided with flattened setae.
The hind legs serve as oars.
9. Fossorial (Digging leg):
e.g. Fore legs of male cricket.
Femur is shout. Tibia is short and shout and bears distally two or three strongly
printed tines.
The first two segments of tarsus are also produced into strong tines.
10. Scansorial (Clining leg):
e.g. All three pairs of legs of head louse.
Tibia is stout
The tarsus is single segmented.
There is a single large claw that usually forms an efficient mechanism for hanging
on to the hairs of host.
