Cossus cossus — “Goat moth”

The goat moth (Cossus cossus) is one of the most prominent European Cossidae. The larvae of this moth don’t feed on the leaves of the host plant – instead they bore though the wood, and live inside trees. This species targets willow (Salix) and oak (Quercus) mainly. The caterpillars of the goat moth have a very long development time – the growth from egg to pupal stage takes 2 to 3 years(!) with this species.

Freshly emerged male of  Cossus cossus 

  • Difficulty rating:  ???/10  —  I am not sure what to rate this.Rearing is very easy, but takes a lot of patience – it can take 6 to 12 months in captivity, and produces a lot of bad smells and waste. However, if done properly it can be  done with almost no losses. While it is possible to produce a good result with basic care, the rearing is still labour intensive and requires a lot of patience. I have never managed to pair this species in captivity. 
  • Host plants: Mainly targets Prunus, Quercus, Salix, Populus but also Juglans, Acer  – but will take many more. 
  • Natural range:  Europe, Asia, Russia 
  • Polyphagous: yes  – especially so in captivity
  • Generations: Univoltine
  • Family: Cossidae (carpenter moths)
  • Pupation: Cocoon (silk encasing) spun in substrate
  • Prefered climate: Temperate
  • Wingspan: 75 – 115mm
  • Special notes: In the wild, the larvae take 2 to 3 years(!!) to mature. However in captivity this can be reduced to 6 – 10 months. This is because they accept fruits, vegetables and bread which have a higher nutritional value than the wood they eat in nature, which consists of a lot of cellulose and is harder to digest. 

Cossus cossus, also known as the goat moth is a large species of carpenter moth found in Europe. The females are attracted to the smell of tree sap (and are sometimes found on moth bait) – despite not being able to feed and having reduced mouthparts. The reason is because they seek out wounded or damaged trees, and sap is an indicator of damage. They will lay eggs in the cracks or damaged bark of trees – it is said that one female can lay over 500 eggs. When the larvae hatch, they infiltrate the tree by boring into the wood, and live their live gnawing tunnels through the tree, feeding on the wood.

Here the larvae can spend 2 to 3 years; due to the hard to digest nature of wood, which consists of a lot of cellulose, the caterpillars need to feed for a long time. However in captivity this can be reduced to 6 – 10 months. The reason this is possible is because they don’t seem to be picky at all and accept a very wide range of food including bread, fruits and vegetables that are much higher in nutritional value than their regular diet.

 Cossus cossus larvae feeding on banana

As the larvae of Cossus cossus like the burrow, they are best reared in any kind of substrate; preferably one they can feed on. Wood chippings/shavings are ideal for this, and they would probably perform well in sawdust too. But this won’t be able to fully sustain the larvae. Besides substrate, they require food; the very polyphagous larvae seem to like all starchy foods such as (brown) bread, potatoes, beets – and they seem to like fruit a lot. The larvae avoid the acidic fruits however, so  Citrus or other fruits with a low PH are not recommended.

The kind of fruit the larvae were most eager to eat include: Kiwi, Apple, Banana – especially banana seemed to be a great succes. The burrowing larvae will even come to the surface of the substrate to feed. They will also burrow or submerge themselves in the food items.

An apple a day keeps the- oh… – Cossus cossus larvae boring through an apple

Here is a possible example of a rearing setup (with bread:)

Cossus feeding on bread; if you look closely you will see one of the slices is being eaten 

Cossus cossus do not seem to care about fungus or mold, amazingly. Even if neglected they will feed on rotting moldy bread or apples, without the slightest care in the world. Which is good news, even though neglecting them is not a good idea – in this kind of setup mold will be hard to avoid, and could be a health risk for the larvae, but such is not the case at all.

Some big fat red larvae!

Note: the larvae of  Cossus cossus can bite and spit stomach acid if startled. They can also scale walls and even glass or plastic containers very well by spinning a silk road.  Beware if you are using an open container; they WILL escape!

After rearing them for a long, long time (for a Lepidopterist that is, beetle breeders may be more familiar with such life cycles) the larvae will spin silk cocoons together and embed some wood/junk in their cocoons.  After pupating they will from wine red/yellowish pupae that will hatch in about a month.

The pupae of Cossus cossus 

The caterpillars of Cossus cossus produce a foul odor in captivity.

Cossus cossus feeding on kiwi

I have no experience pairing the adults, as they emerged quite sporadic due to the individual growth speed of the larvae. Pairing the adults however may prove difficult. Females are significantly larger than males.

Cossus cossus male reared in captivity

Rearing example: (oops sorry for the music)

 

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The aim of this website is to provide information about many species of moths and butterflies around the world, with a slight focus on rearing them in captivity.

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