Scientists from the University of Utah have identified the caddisfly’s secret to underwater stickiness.
Caddisflies comprise thousands of species of insects in the order Trichoptera. They lay their eggs in water, where the larvae grow and develop. Many species use their silk to construct underwater tubes of sand or leaf debris. The larva lives protected in the tube, and eventually seals the tube off to pupate within it.
Caddisfly larva with underwater mobile home made of sand, rock grains and glass beads.
Credit: Fred Hayes
Russell Stewart and his lab used the caddisfly Brachycentrus echo as a study subject. This species drags its case of silk and rock around with it as it forages for food, ready to dive into the safety of the tube at any moment. The researchers found that the B. echo larvae were able to attach their ribbons of silk to all manner of organic and inorganic materials, all underwater.
A mesh of wet adhesive silk ribbon produced by a caddisfly larva to stitch together the inside of its shelter case, made with glass beads it was given in a laboratory aquarium.
Credit: University of Utah
Apparently, the silk ribbons are laid along the inside of the tube shelters like tape. Upon further study, including electron microscopy, the scientists found that the caddisfly silk protein was largely made of phosphorylated serine. The negatively charged phosphate groups line up across from other positively charged amino acids creating the silk ribbons.
Although the exact mechanism for allowing the silks to stick to things when wet is not yet understood, the researchers have observed that dry silks made from moths and butterflies do not contain phosphorylated serine. In fact, phosphates have been used to increase the adhesion of paints or dental fixtures.
As Stewart says:
The association of those plus or minus charges makes them water-insoluble. This is how you make a silk fiber under water.