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#13: Insect Legs



Litinsects #13: Insect Legs

Insect legs can be as diverse as the animals themselves. Some are long and slender like a crane fly’s, some are short and hefty like a mole cricket’s.

But what all insects share is the number and layout of those legs. Hexapods have 6 LEGS, a pair each of fore, mid, and hind legs that are made up of the same basic units. Starting closest to the body, they are: 
(1) the coxa, which attaches the leg to the thorax 
(2) the trochanter
(3) the femur, which is often the thickest segment 
(4) the tibia, often covered in tiny hairs
(5) the tarsus, which contains 5 “pseudo-segments” 
(6) the pretarsal claws, of which most insects have 2 on each leg

The basic units of the leg always occur in this order but may be reduced or highly modified in some species to fit certain tasks such as running, digging, swimming, grasping, or jumping. This photo sums it up perfectly:

from <https://wiki.bugwood.org/File:Insect_legs.jpg>

The functions of the legs are as follows:
(A) running
(B) jumping
(C) digging
(D) grasping prey
(E) catching
(F) walking and digging
(G) walking and digging (with reduced units)
(H) grasping females during mating

Learning about how insects walk was a genuinely fascinating moments for me because it just makes perfect sense... See, insects most commonly use a TRIPOD GAIT to walk, meaning that 3 legs are always in contact with the ground. To move, they step with the fore and hind legs of one side and the mid leg of the other side all at once, keeping the opposite legs on the ground. Because the insect’s center of mass always stays within the tripod, this is an extremely stable gait. 

So practical is this style of walking, that insects have inspired many types of HEXAPOD ROBOTS for tasks involving difficult terrain. A tripod is the most practical and stable form to build with legs so it only makes sense that this is ideal for navigating tricky surfaces! 

So the next time you see a slow-moving insect, try to watch its feet and see if you can spot the tripod!
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