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."
The Chemistry and Structure of Wet Silk from Caddisflies
Stewart's study included detailed analysis of the chemistry and structure of the caddisfly silk, showing how it is similar to what silkworm moths produce for use in textiles and even to spider web silk, but with adaptations that make it work underwater.
Stewart says his goal was to characterize the adhesive silk fiber "for the purpose of trying to copy it" so a synthetic version can be used as a surgical adhesive.
he found the caddisfly silk is a fiber made of large proteins named fibroin (fye-bro-in) with an amino acid named serin
|Contact: Lee Siegel|
University of Utah