Fleas are wingless insects and cannot fly. They are small and look like a cross between a lobster and an insect. They have a thick, crustacean-like underbelly and four sturdy legs. Four of these legs are located on the sides, where they can easily crawl, while the other two are on the back, where they can leap. Despite their size, fleas are able to jump up to eight inches in one jump.
Fleas originally had wings, but as they became resident parasites, they were unable to fly. However, they retained many of the structures of flying insects, such as the pleural arch, which acts as a hinge ligament. This ligament also contains resillin protein, which stores energy that fleas need to jump. Hence, it is believed that the evolution of fleas began at an early stage when their wings were not functional and were a hindrance.
Compared to other insects that can fly, fleas are highly energy-efficient. Their legs are not strong enough to pull them out of sticky situations, so they must rely on their jumping capabilities to reach their hosts. They can detect their host by observing the differences in light, and then extend their middle pair of legs in the direction of their target. Once they land, they will latch on to the fur of the host.
Fleas can jump quite high, but they prefer to stay in their host’s fur, where they will stay warm. This is because their wings are unable to fly on their own.