Cossus cossus

Notes on the Goat Moth.

The Goat Moth, Cossus cossus, is different from many of your standard moth species in that it’s larvae remain hidden from view their entire development. In the wild they feed up on dead and dying willow and poplar trees, taking several years to mature. However in captivity, with a bit of thought, they can be reared right through in a single year. Whenever I raised this species I did so in my old garage, which was sort of cool in summer and yet not too freezing in winter. Plastic tubs are ideal, as if you use wood the larvae can chew out, as their teeth are very sharp and powerful, obviously chewing through wood is what they’re designed for! Ova hatch after a couple of week, with tiny red larvae setting off to search for somewhere to burrow into. In the wild this would be a stump, but I gave them a swede cut in half and they took to that easily. What I actually did was to hollow a little bit of the lower part of the swede (turnip) out and place a few larvae in before covering it up with the lid. Sort of trapping them inside, and it really worked. I then placed the swede in a plastic tub on top of hardwood sawdust, or sometimes some peat. The very next day I had a little peek and all larvae has vanished into the swede, which was exactly what I wanted. Now, I know there’s other methods, and I’d tried a few, such as using apple and brown bread and beetroot. However I found swede the best, it holds its shape for longer and doesn’t descend into a sopping wet mess like apple does. These larvae feed well, eating a large amount, and I added ‘new’ swede as I went. This was done by placing halved swedes onto the remains of the eaten one, and the larvae soon burrowed into the new one. They grow quickly, and look a formidable sight with their deep red bodies and their shiny black jaws. I never got bitten by one, but I reckon it would have hurt! As winter came along the larvae seemed to stop feeding and I left them until the following spring. They seem to spend the cold months in a very loosely spun cell of shredded swede. As the worst of the winter came to an end and the days warmed the plump larvae made a pupal cell in which to metamorphose. The larvae would build the cell from whatever substrate was available, be it sawdust or soil, and inside it settled down to pupate. A few weeks later and I was greeted one morning with the first of many imago sat on the mesh of the emergence cage. The very next night these started pairing, which required no input from me, apart from leaving the window ajar. Although I have had much success getting female moths to lay in unfurnished cages I placed a few pieces of willow bark in the cage too just to see if there was any difference. The cage top and sides were splattered with eggs and there was quite a few laid on the bark also. But all things considered I don’t think bark is needed. The ova take the standard few weeks to hatch and the cycle repeats itself once more. This species is wonderful, the larval stage really must be experienced to believe how interesting it is and it’s a species I’d strongly recommend everyone to try and rear at least once in their lifetime.