[MUSIC] Insects have efficient musculature that powers their movement. As with many features we've come across so far, the number of muscles in an insect body varies with the species and life stages. Most insects have many more muscles than vertebrates because each body segment has its own set of musculature and some caterpillars even have thousands. The muscles operate in tandem with the exoskeletal system to which they are attached. The rigid exoskeleton provides the muscles with leverage to move different parts of the insect's body. Insect muscles are connected to the inner surface of the exoskeleton where the cuticle is strengthened with thick ridges called apodemes. The muscle attachment sites can also contain resilin, an elastic protein that plays a role similar to tendons in vertebrates. Insect muscles are very efficient. Think about a flea's ability to jump up to a 160 times its body length and the fact that the two strongest animals on Earth for their body size are both insects. The male dung beetle pulls over 1,100 times its body weight while rhinoceros beetles are able to lift up to 850 times their weight. These impressive athletic feats are possible not because insect muscles are inherently stronger but because the muscles are more efficient due to the insect's small size. How does this work? Let's break it down by looking at the relationship between power and body mass. The first thing to be aware of is that the power of a muscle varies with the size of its cross-sectional area, which would be the square of its width. Meanwhile, the entire body mass of the insect which the muscles are moving varies with muscle volume and mass. As such, when body size decreases the associated reductions in muscle power and volume are not equal. Let's visualize this by imagining an insect muscle as a cube measuring three units long on all sides. At this size, the volume of the muscles is equal to the cube of its width while the cross-sectional area of the muscle is the square of its width. Let's shrink the cube. Now both the volume, as well as its cross-sectional area, have decreased, but notice that the decreases are not proportional. In fact, volume decreases more rapidly than the cross-sectional area. This means that the muscle is now more powerful per unit of mass than it was when it was larger and heavier. When this concept is applied to the insect as a whole its muscles become relatively more powerful as insect body size is reduced. It is therefore probably more accurate to say that insects are deceptively strong, not despite their small body size but because of it. We've talked about how insect muscles operate with the aid of a rigid exoskeleton, but what about larval insects? How do they move when their soft exoskeleton lacks the rigidity net needed for muscle leverage? In these soft-bodied insects movement is achieved using a hydrostatic skeleton in which muscles are attached to and within the body walls. Unlike the exoskeletal muscle system in most insects which operates on rigidity, the hydrostatic skeleton operates on turgidity. In this case, body shape is supported by muscles in the body wall that contract to create pressure opposed by the incompressible hemolymph. When muscles contract in one part of the body it causes an extension in another relaxed part of the body. As the muscles continue to contract and relax in sequential waves this creates either an undulating or sinusoidal snake-like motion of the larvae. Together with hooks, spikes, and sometimes mouthparts these motions allow the larvae to grip the substrate as they move. The same motions also allow some insects, such as mosquito larvae, to swim in aquatic environments. Muscles are key to insect locomotion as they provide the strength and precision to power movement in the legs and wings. We'll begin to discuss these locomotory appendages in the next video starting with insect legs.