The mystery of a flea's jump

 One of the great mysteries of nature that was cleared up in my lifetime was the flea’s jump.

Imagine that I am kneeling on the goal line of a football feel. I jump, using my impressive muscles, 300 feet into the air — as high as the football field is long — and end up beyond the opposite endzone, 120 yards away.

To scale, that’s what a flea does. It jumps upward 50 times its length and goes downfield 60 times its length. Physiologists who examined the flea’s leg muscles said they were more impressive than mine but not that impressive. What was going on?

Fleas were once flying insects. Flight muscles are enormous. If human beings had them, they would extend 6 feet out from our shoulders. More than 160 million years ago, fleas converted that relatively big reservoir of muscle that controlled their wings into a jumping mechanism. (That reservoir, filled with an interesting protein that acts like a spring, is inside the exoskeleton.)

The change in physiology occurred with a change in diet. Fleas once ate plants. If your new food is mammal blood and your strategy for getting it to bushwhack your victim as it passes through dense vegetation, jumping is more efficient than flying. The vegetation provides too many obstacles to flight.

I did not know, until I read Erica McAlister and Adrian Washbourne’s account, that Miriam Rothschild had done so much in sorting the mystery out. She was carrying on the work of her father, Charles Rothschild, a London banker who managed to identify 500 new species of fleas before his death in 1923.

It’s fascinating what can catch the interest of a person’s mind.

• Source: Erica McAlister with Adrian Washbourne, Metamorphosis: How Insects Are Changing Our World; Washington, D.C.: Smithsonian Books, 2024.