Three factors normally promote good breeding results

Healthy plant growth is promoted by potting up younger plants using potting compost available from garden centres. Such compost would normally be free of pests or weeds. To keep the soil free of pests it is advisable to place a pad of thin fibre-mat, obtainable from garden centres, inside the base of the pot to cover the holes. This keeps pests out and still allows free passage of water and air. Aphids on plants can be killed by using Zeneca " Rapid " spray as directed, but not with larvae present. (Note; manufacture of this insecticide unfortunately appears to have been recently discontinued, leaving no equivalent product) - Leave the plants for 2 days before introducing larvae. Most other insecticides will kill larvae many weeks after application - even if the instructions state that foliage may be eaten (by humans) after a few days! Clip off old straggly growth and feed the plant regularly with liquid fertiliser such as ''Miracle-Gro'' to promote the young growth which most larvae prefer. Water the plants regularly. If the plant is all consumed, it is possible, as an expedient, to add cut plant in a water jar, using a wad of cotton wool in the neck of the jar to prevent the larvae drowning. Add the cut plant by opening the sleeve top and reaching down to place the jar on the soil.

Predators may be present in the plant or soil, perhaps because the plant was left unsleeved, or it was necessary to use a soil other than potting compost. A surprising range of carnivorous beetles, centipedes, earwigs, ants and spiders can accumulate in the pot to consume your ova or larvae. and woodlice can also disturb caterpillars. Weevil larvae can kill the plant by eating the roots, and slugs eat the leaves. These can be mainly avoided by totally immersing the pot, soil and plant in water for 2 days before introducing the larvae. Mostly these unwanted visitors float off and can easily be hand picked. Those that don't generally drown themselves.

Keeping an appropriate temperature and humidity are important. Natural outside conditions are usually best for British species. Some species, such as downland types, thrive in good sunlight. Others, for example woodland species, require shade and may dry up and die in strong summer sunlight. Under greenhouse conditions, or in a sunny indoor window, very hot and dry conditions may be created which can quickly kill larvae which expose themselves; for example young Peacock or Small Tortoiseshell larvae.
If in doubt, it is safest to choose light but shaded situations.

Happy rearing!