You may know the caddisfly as one of the flies that fly fishers emulate when creating lures. (Trout love them.) But when this fly is in its larval stage, it does something special: Caddisfly larvae build armor out of pebbles and sand.

Much like hermit crabs, the caddisfly larvae repurpose existing items to make a safe home. In order to create their "armor," the larvae use sticky silk to stitch the pieces together. This silk is remarkable, because it only sticks to the rocks, and it remains flexible underwater. This comes in handy because the larvae tend to live in very high-current areas, which can fling them around. When the larvae are ready to transform into adults, they attach their armored shell to an underwater surface and pupate inside.

The properties of caddisfly silk may be useful in medical research; we're still trying to make something like it. In this Ultra HD (4K) video, Deep Look takes us into the tiny, sticky world of the caddisfly. Enjoy:

Incidentally, it's tough making a video about tiny underwater larvae living in extreme currents. Here's a making-of video from Deep Look, explaining just how they did it!

For more (or if you're not into watching videos), check out this KQED Science story about the caddisfly.