Not all fleas jump. Several species of bat fleas almost never perform jumps. For them, jumping is disadvantageous and dangerous, as they live in high aerial roosts and are blind. Similarly, fleas of swallows and flying squirrels rarely jump.
Fleas of dogs and cats are some of the best jumpers. Non-jumping insects discovered within homes likely aren’t fleas.
The Jumping Mechanism of Fleas
Pleural Arch & Resilin
Fleas’ hind legs are their primary source of jumping power. However, to execute large jumps, take-off is greatly accelerated by energy stored up in, and released from, a highly elastic protein called resilin. The resilin is located within a structure called the pleural arch.
Poor Jumpers have Reduced Pleural Arches
Pleural arch size and jumping ability are often correlated. In flea species that are poor jumpers, the pleural arch and resilin are missing or diminished. However, even without the booster mechanism, they’re able to make small leaps with the muscular system of their legs.
Flea Evolution & Jumping
Fleas Co-Evolved with their Preferred Host
The jumping performance of fleas varies greatly among species. Each species co-evolved along with their preferred host. As a result, they have structural features that are adapted to their host’s environment and behaviors.
Good Jumpers Parasitize Large Animals
The best jumpers parasitize large animals without a well-defined nest. Since there’s no nest, the fleas live on the host’s body. However, in order to initially acquire a sizable, wandering host, the fleas must be able to execute large jumps. As a result, the resilin and pleural arch must be well developed.
Poor Jumpers Parasitize Flying or Nesting Animals
The poorest jumpers parasitize flying and gliding hosts which live in high aerial nests, such as bats, swallows, and squirrels. Jumping would be disadvantageous and dangerous for these fleas. Thus, they often lack a pleural arch and resilin.
Similarly, fleas of moles, desert rodents, and other nesting animals (nest fleas) are poor jumpers with reduced pleural arches. These hosts rarely leave their nest or burrow, so fleas don’t need to jump to acquire a blood meal.
All of these fleas species are more well adapted for crawling than for jumping.
Bat Fleas are the Worst Jumpers
No Plural Arch or Resilin
Fleas which parasitize bats rarely jump at all. Many bat fleas species don’t have a pleural arch or resilin. Their jumping performance is poor, and jumps are an extremely rare occurrence.
Jumps are Rare & Feeble
Bat fleas sometimes jump in response to harassment (being blown upon). However, these rare jumps are weak, with maximum distance of 66 mm. Additionally, jumping has only been observed in newly-emerged adults. Once a host is acquired, they won’t jump at all.
Jumping is Dangerous
Bat fleas are blind cave dwellers. The larvae live in bat guano. Upon maturing, the adults must ascend the cave walls to reach their hosts in bat roosts. In this situation, jumping would be less useful and more dangerous than climbing, which explains why they don’t jump.
Bat Fleas are Adapted for Climbing & Crawling
Though they’re the worst jumpers, bat fleas are good climbers and walkers. Like many cave-dwelling insects, they’ve developed long, thin, delicate legs. The spindly legs are well-suited for climbing, not jumping. In addition, bat fleas have a long, flexible thorax, which is another crawling adaptation.