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Rearing caterpillars

Brown-tail moth caterpillar (Euproctis chrysorrhoea). The hairs can cause a skin rash.

There are over 140,000 species of Butterfly and Moth (Order: Lepidoptera) in the World. They include some of the largest and most beautiful insects to some of the smallest and most easily over-looked (unless you're an entomologist). Caterpillars are the main feeding stage in the life cycle of butterflies and moths, and make one of the best "Creepy Crawly" pets.

Obtaining caterpillars

Caterpillars of many different moth and butterfly species can be obtained by post from many good entomological suppliers. However, many excellent caterpillars can be found by searching plants or bushes during spring and early summer. When you find a caterpillar remove the plant stem that it is feeding on and place this is a suitable carrying vessel (eg. jam jar or sweet jar - with a lid!). Do not try and pick up the caterpillar with your fingers as they are quite delicate and many possess urticating hairs or secretions that will irritate your skin - collecting the stem they're on is much safer.

Do not take lots of caterpillars from a particular site, five is probably a maximum and the number taken depends on the size of enclosure you have prepared at home before collecting the caterpillars. It is also important that you identify the food plant the caterpillar was found on and also take some stems to put in the enclosure.

If you find a caterpillar wandering along the ground then it is either searching for a food plant or looking for somewhere to pupate. If it is small then it is best not to collect it unless you know the species of caterpillar and the plant that it feeds on. Note: there are many, many species of "small green caterpillar" and unless you know exactly which one it is then it is likely to starve to death because you can't provide it with the correct food plant.

Housing

This depends on the size of your caterpillars and how big they grow - you may need to re-house your pets as they get larger. Normally a tall sweet jar will be ideal, drill some small (i.e. smaller than the caterpillars) holes in the lid (get an adult to help you) and place the stems of the food plant in a small jar full of water. It may be a good idea to block the top of the small jar with cotton wool to stop your pets falling in and drowning. If your caterpillars are very small then you can use a block of oasis (a type of hard green sponge used for flower arranging) soaked in water and with the stems pushed into it instead.

Once the food plant is placed in the larger jar then you can gently introduce your caterpillars - again using the stem they are sitting on. It is also an idea to place a twig in the large jar so that should the caterpillars fall of the stems they can climb up the twig back to their food plants.

If you have a tropical species which you ordered from a supplier then it is best to keep them indoors and they may even require more specialised conditions (consult your supplier). If you found your caterpillar outside your house then you can keep your cage outside however you must be very careful that it will not blow over in the wind or fill with water when it rains.

You should spray the cage lightly with water once a day or so, however avoid large quantities of condensation forming on the inside of the container. Caterpillars can easily drown in condensation, remember that to caterpillars, a blob of water is very much like a lump of syrup.

Feeding

The majority of caterpillars are herbivores (ie they eat vegetation) although many will become cannibals if not given enough food plant. Aside from cannibalistic tendencies some caterpillars will kill and eat caterpillars of other species of moth and butterfly and it is best to keep them singularly (e.g. Anthocharis cardamines - the Orange Tip Butterfly).

Caterpillars are very particular about what they eat. Individual caterpillar species have a particular type of food plant (or family of plants) that it is associated with. Caterpillars will only eat very specific plants, which is why you must remember what plant you collected the caterpillar from - it is a good idea to identify the plant from a book or collect and press a stem for reference as your caterpillar grows.

As your caterpillars grow they will require more and more food so it is a good idea to make sure you have a good supply of the food plant before contemplating keeping the caterpillar. Remember that the larger the caterpillars get the more they will eat. Caterpillars increase in size by moulting so don't be concerned if you see some with small bits of their old skin still attached.

As soon as most of the food plant has been eaten or if it starts to wilt you must change it for fresh leaves etc. The replacement food should be exactly the same plant as before otherwise your caterpillar may not eat it. It is also a good idea to wash the food plant thoroughly before giving it to your pets. I cannot stress enough how important it is that you feed your caterpillar the correct food plant.

Pupation

The pupa of the Large Copper _Lycaena dispar_

The pupa of the Large Copper butterfly Lycaena dispar.

Butterflies and moths undergo complete metamorphosis and caterpillars must pupate as a chrysalis (or pupae) before becoming an adult (imago). During pupation almost all of the caterpillar is broken down and the resulting 'nutrient soup' rebuilt into the body of the adult insect.

When the caterpillars are full-grown they should be provided with suitable pupation sites. Butterfly caterpillars should be given stems and branches from which to suspend their pupae. Many moths produce larvae that burrow into the soil to pupate so these species should be provided with a thick layer of damp earth. Other larvae should be provided with foliage or bark depending on the species. If you are unsure of your caterpillar's requirements it is best to present them with a choice of pupation sites.

Pupae that have formed during the spring or early summer should hatch within a few weeks. Pupae that formed during the autumn will overwinter and should be removed from the cage and stored to prevent them drying out or going mouldy. The pupae should be placed in layers of earth in small sealed containers; these should be kept in a cool but frost-free place (such as an unheated shed) until the following spring. In spring the pupae should be slightly embedded into a layer of earth or placed between the grooves of a sheet of corrugated cardboard. They should be misted with water occasionally to produce a humid atmosphere and this can be used to induce the emergence of adults.

Emergence

When the adults are about to emerge you should place a number of twigs and stems in the emergence tank. The twigs are required by the butterflies and moths to climb up before expanding and drying their wings. If no suitable supports are available then your butterflies and moths will have deformed wings and be unable to fly.

If you collected your caterpillars from the wild then you should release the emerged adults (or imagos) in the same area as you collected the caterpillars. When releasing butterflies, and especially moths, during the day make sure they are released in secluded areas so that they are not immediately eaten by birds.

If you obtained your caterpillars from an entomological supplier you could try and breed them to produce another generation of insects - you should not release them into the wild. Information on breeding butterflies and moths will be available from the supplier of the caterpillars and from a number of our publications.

Mating butterflies at the London Butterfly House.

Further information on Butterflies and Moths.

Essential reading

Remember: it is important that you know the needs and requirements of your pet before you obtain the animal. You should never, ever obtain an animal before researching its needs and preparing the housing and conditions.

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