Sticky. Stretchy. Waterproof. The Amazing Underwater Tape of the Caddisfly | Deep Look


To us, it’s a tranquil mountain stream… But if you’re a bug living on those algae-covered
rocks in the water? It’s a constant underwater hurricane. Powerful currents. Debris swirling all around you. How do you survive? Well, you build a shelter. All you need are some raw materials…and
a little tape. That’s right. Tape. This is the larva of the caddisfly. This insect has evolved a tool that’s eluded us humans so far: tape that stays sticky underwater. As winged adults, caddisflies are a favorite
food for trout. Artificial lures mimic them in painstaking
detail. But they spend most of their lives as larvae
in shallow, turbulent water, which is rich in the oxygen they need. And though its head and legs are covered in
a thick layer of insect armor, or chitin… …its soft, white lower body is more exposed. To the elements, and especially to any passing
predators. So the caddisfly has figured out how to build a case…for ballast, protection, and camouflage. It does this by binding together pebbles with
a special silk that looks, and acts, a lot like double-sided, waterproof tape. Every case starts with one pebble. It’s like…the cornerstone of a building. The caddisfly adds more pebbles, one by one,
like a bricklayer putting up a wall, using its tape as the mortar. When he brushes the surface with his mouth,
that’s his tape dispenser working. It’s in a gland under his chin. He’s sealing the pebble down. These flies are VERY particular about their
building stones. Only the right shape and size will do. If it doesn’t fit, it’s out. When he finds a match, he fits it into place. Once he tapes down the basic shape of the
case, he seals it up from the inside, in a series of barrel-roll maneuvers. The problem with our tape is that when it’s
wet, it loses its stick. But caddisfly tape is selective. It sticks to pebbles, but not to water. What’s more, the ribbon itself is like a
rubber band. It can stretch to twice its size and return
to the same shape. But it snaps back slowwwwwwly. It’s a rubber band that moves like molasses. So the case is resilient. No quick movements. That’s a lot safer for the vulnerable larva
living inside. Bio-engineers have started to figure out how
we could make our own caddisfly silk. Maybe as as a kind of internal surgeon’s
tape. To replace the metal and string that we use
to patch people up now. The magical underwater tape of the caddisfly. Another example of how evolution finds radical
solutions to everyday problems. Like how to survive in a hurricane. Hi, it’s Amy. Look how tiny these guys are! That’s what we do at Deep Look: zoom way
way in to very small worlds. If you like it, subscribe! And leave us a comment down below. Thanks so much for watching.

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