(Describer) Logos appear: KQED; PBS. A title: Deep Look. A flea's face appears to have a row of fangs along its mouth. A cat wanders past.

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NARRATOR: Sometimes to get where you want in life, you need to go all out. Fleas need to get off the ground and onto someone they can exploit.

(Describer) Animals scratch.

That's bad news if you've got fur or feathers. There are more than 2,000 flea species, each partial to its own kind of creature. But the one you'll most likely cross paths with is the cat flea. Fleas are one of nature's greatest jumpers, taking a gigantic leap almost too fast to comprehend. They're small and narrow, like a little sesame seed with legs. Their fly ancestors lost their wings millions of years ago to help them slip through fur with ease.

(Describer) Tiny specks appear in the cat's fur.

Fleas are tough to get rid of. Stiff backwards facing hairs catch on fur when you try to pick them out. Try to squish one?

(Describer) A person presses thumb and finger together hard. The flea crawls right out and jumps.

Nope. They're flexible bodies are armored with rugged plates called sclerites. Adult fleas only eat one thing--blood.

(Describer) A person uses a flea comb on the cat. It wriggles between the comb's teeth.

This cat flea prefers cat blood. But in a pinch, it will latch on you too.

(Describer) A flea lowers its head against human skin. A drop of red fluid squirts from the tip of its abdomen.

They lay eggs that drop from the cat's body into its bedding.

(Describer) Like a tiny, white jelly-bean.

A few days later, they hatch. And worm-like larvae wiggle out. The hungry larvae scavenge for food. Their favorite meal comes from Mom and Dad-- adult flea poop. That's just semi-digested blood.

(Describer) A brown coil in the cat-bed.

Now who could turn that down?

(Describer) The worm-like larva wriggles through the bedding and nibbles on the flea-poop.

The larva curls up in a cocoon it makes from whatever dirt, sand, or other materials it finds nearby. A few days later... violà, all grown up.

(Describer) A young flea emerges.

Now this hungry flea needs a warm body to call home. Its jump is super fast, 100 times faster than the blink of an eye. But it takes more than muscle to move that fast. The flea can compress itself like a spring thanks to a rubbery protein called resilin in its legs and body. First, the flea pulls in its oversized rear legs and locks them in place. It squeezes and flattens its body, squishing the resilin and building up energy for the jump. Then... it releases the energy all at once. The flea tumbles through the air, legs extended. With a lot of effort and a little luck, it will land on its target, and the whole incredibly itchy cycle will begin again.

(Describer) The flea wriggles into cat fur. Credits appear: Producer/Writer/Cinematographer: Josh Cassidy. Narrator/Writer: Laura Klivans . Original Music: Seth Samuel. Lead Producer: Josh Cassidy. Funding for KQED Science is provided by the National Science Foundation. Copyright 2020 KQED Inc. kqed.org/DeepLook. Accessibility provided by the U.S. Department of Education.

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