William L. Coleman, Animals That Show and Tell, Bethany House, 1985, p. 110-111
One of the most unusual homebuilders is the caddis, which builds an underwater home out of pebbles and glues them together for strength. A mother caddis will lay hundreds of eggs in the water. She looks much like a butterfly but usually lacks the bright colors. There are 3,000 different types of caddis. The caddis spends most of its life as a youngster. It is in the larva stage for an entire year, but may live less than a month as an adult. Not every caddis larva builds a strong home. Some are content with nests. But if you build a home in a mountain stream, you had better make sure the stones will stick together. This is where the caddis’ special glue kit comes in handy. An unusual cement-like paste comes out of its head, and the caddis applies this to the stones. The glue is water-resistant and strong enough to hold under water. When the young caddis starts to construct its home, it begins by looking for bright- colored pebbles. Red, white, and black stones are gathered for the project, and other shiny objects might be added. A baby caddis fly would be an easy victim for any fish that wandered along. In fact , a caddis’s main purpose may be food for other fish. But while many creatures would simply hide in any place that is open, the caddis would rather have a stable home that is built correctly and offers the most protection.
You might see a caddis if you visit the mountains, but you have to know what to look for. As adults they leave the water and fly. They look a great deal like moths.
How does a baby or larva caddis know how to build a stone house and glue it together ? Somewhere God placed an instinct in the caddis that allows it to drive toward that goal. And since it already has the glue in its head, this becomes the natural urge to follow. If a caddis is to depend on its stone house, the cement or glue has to to hold. It must be adhesive and yet water-resistant at the same time. If it did not hold, the house could crumble and fish would eat the caddis. When some things do not hold the result is often disaster. The Bible tells us to hold on to the good and godly things in life.