You might recall from the previous module on insect external morphology that the thorax is the locomotory tagma of the insect body because it bears the legs and wings. Specifically, most adult insects have six legs that are attached in pairs to each of the three thoracic segments. The prothorax, mesothorax, and metathorax. Insect legs are appendages with six segments. The most proximal segment or the one closest to the body is the coxa. Moving away from the body, we have the trochanter, femur, tibia, tarsus, and finally the pretarsus at the tip of the leg. Each segment has internal musculature so that it can move independently. Musculature to move the entire leg attaches from the insect sternum to the coxa. Insect legs are usually positioned in a wide stance on either side of the body for better support and leverage. Although the stance is wide, the leg bases are located ventrally on the body which allows neuromuscular mechanisms that manage leg movement to exist close together for better efficiency and control. When insects walk, they maintain continuous contact with the ground. The fore and hind legs on one side of the body and the mid leg of the opposite side push in emotion known as retraction. Meanwhile, the remaining legs are lifted from the substrate and move forwards in a process known as protraction. This walking motion is called the tripod gait. It keeps the insect center of gravity within a tripod stance which provides greater stability. Considering the wide variety of environments insects can live in, it should not surprise you to learn that insect legs have evolved for locomotion in different types of habitats. Modifications often involve changes in individual legs segments which can be enhanced, reduced, or variously shaped for specialized functions. In some cases, the legs may even be modified for non locomotory purposes. The most basic insect legs are cursorial or running legs. Cursorial legs are usually elongate and slim, and have a well-developed femur and tibia. The length of these legs allow the insects to cover a lot of ground with relatively few steps. Additionally, the leg's slim profile contributes to an increased stride frequency as there is a reduction in weight at the distal end to be swung back and forth. A good example of an insect with cursorial legs is the cockroach. In some insects, the legs are modified not for locomotion but for grasping prey or mates. These are called raptorial legs, and spines are often present on the tibia and femur to allow better grip. Insects with these types of legs tend to be predatory. This modification usually occurs in the forelegs, although, some predateous flies have raptorial hind legs to grasp prey. A well-known example of an insect with raptorial legs is the praying mantis. Thanks to the special foreleg modification along with other adaptations, praying mantises are extremely successful predators. They are so efficient at hunting. Some species of praying mantises actually prey on hummingbirds and mice. Some insects that live underground have powerful forelegs to dig through the soil, called fossorial legs. The tibia in this specialized leg type is usually flattened, enlarged, and heavily scleratized with tooth-like projections on the outside that allow the insect to rake soil. The tarsi are also greatly reduced which keeps them out of the way during excavation. The appropriately named mole crickets live in underground burrows and have well-developed fossorial legs. Jumping legs or saltatorial legs are a specialized type of hind leg. The femur and tibia are greatly enlarged in saltatorial legs to house powerful muscles that quickly release large amounts of stored energy, allowing the insect to jump incredible distances. These legs may also have elastic components such as resilin which allow the storage of even greater amounts of potential energy. We can clearly see saltatorial legs in most orthopterans, and we've already come across other examples when we learned about the incredible acrobatics of fleas and treehoppers in previous lessons. Some insects that live in aquatic habitats have specialized mid or hind legs for moving in water known as natatorial legs. These legs are often flattened and have fringes or rows of setae to increase surface area. Natatorial legs are modified to operate like little oars that allow the insect to paddle underwater. The legs are moved in a specific pattern that reduces surface area on the recovery stroke while increasing surface area on the power stroke for better efficiency while swimming. This is the same technique that rowers use when moving their oars in, through, and out of the water. Diving beetles and water boatmen are good examples of insects with natatorial legs. Another type of locomotory appendage found in some juvenile insects is the proleg or larvapod. Prolegs are modified extensions of the body wall and are generally found on larvae of certain groups of insects such as the Lepidoptera, Hymenoptera and Diptera. Some prolegs have hooks or crochets at the distal ends that allow the larvae to better grip the substrate. Prolegs are not true legs for two reasons. First, unlike true insect legs, they are not attached to the insect's thorax. Secondly, prolegs are not jointed, and therefore lack the six segments we described earlier that are characteristic of true insect legs. Now that we've dug through the diverse modifications of insect legs from different habitats, let's shift our attention to the other major locomotory appendages of insects - wings. Over the next few videos, we'll focus on the structure and modifications of insect wings, and explore the complex ways in which insects achieve flight.
