The moth in a case

From time to time a creature turns up that just doesn't seem to fit into the framework of one's experience. This photo is of such a specimen. It looks like a caddis larvae though I found it on a cherry leaf. Caddis normally live in streams as larvae where they protect themselves with small pieces of sticks. My search for identification led me to contact knowledgeable French naturalists. Like this friends are made. It transpired that it was a caterpillar of a moth of the group Psychidae. To the right of the case you can just make out the hind segments of the body of the creature. The story becomes more interesting. Just below the case there are scattered eggs. Caterpillars do not lay eggs. This could not be a caterpillar. I observed the creature in the act of laying the eggs. At its rear end was a large brush of thick finger like processes. From between these extruded an ovipositor which it could extend to a length longer than its body. This it waved it about like a hose until it touched the leaf surface. Then an egg passed down the tube. And it then repeated the act. Obviously it was a female. Was it trapped at the time of its emergence and transformation from the chrysalid stage by its own case of sticks? I gently removed the sticks and found that this was unlikely and moreover I discovered that this female had no wings.

I went back to read a paper on this group supplied to me by my French friends. It seems that the female never leaves the case (French - fourreau) and that a male seeks it out and mates with her in situ. It could be that the finger like processes exude an odour to attract the males. In some related species the female retains its larval form and looks like a worm. Apparently the adults never feed. The female doesn't leave the larval case and the male has imperfectly formed mouth parts.

So far so good. What do the caterpillars eat? The cherry leaf had not been eaten and the sticks of the case looked like fragments of grass stem. I suppose that the insect fed on the ground and climbed more than a metre up the young cherry tree to pupate. What happens to the caterpillars that emerge from the eggs? Do they fall to the ground? How far do the caterpillars crawl to extend the population? The pattern of life where a female of an insect species is flightless is fairly common. It must suggest that there are extensive areas of habitat suitable for feeding. If not the species must surely become extinct.

pasque flower

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