Stewart and study co-author Ching Shuen Wang - who works in Stewart's lab - studied the caddisfly species B. echo from the lower Provo River about an hour south of Salt Lake City. Bioengineering undergraduate student Nick Ashton gathered the fly larvae and figured out how to keep them alive in the lab.
"There's just a fascinating diversity of these insects. Their adhesive is able to bond to a wide range of surfaces underwater: soft and hard, organic and inorganic. If we could copy this adhesive it would be useful on a wide range of tissue types."
Caddisfly larvae extrude adhesive silk ribbon out of an organ known as the spinneret. The products of two silk glands converge there, so the extruded adhesive looks like a double ribbon with a seam the long way. The larvae weave this sticky mesh back and forth around sand grains, sticks or leaf pieces to create the tubes they occupy. Stewart and colleagues grew caddisfly larvae in aquariums, but with glass beads instead of the sand and rock grains found in streams. The larvae expanded their rock cases using the beads, which were glued together from the inside by wet silk ribbons.
The researchers broke off some beads to obtain clean samples of silk. They analyzed the silk using several methods, including scanning electron microscopy, which showed how silk fibers stitched together the glass beads from inside of the shelter case. "It's like using Scotch tape on the inside of a box to hold it together," Stewart says. "It's really like a tape more than anything else - a tape that works underwater."
Stewart hasn't studied the strength of the caddisfly silk, but plans to do so. "Individual threads aren't very strong, but it lays down dozens of them. If we can copy this material and make tape out of it, the bond strength would go up dramatically."
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