Gardens: caterpillars as pets

If the sight of a caterpillar has you reaching for the bug spray, maybe it's time to change your outlook. Rather than seeing them as pests hell-bent on destroying your lovingly nurtured plants, look on them as a sign of a healthy garden ecosystem, the future generation of butterflies and moths as well as food for baby birds. What's more, caterpillars can also be used to engage your children with nature, and make a great project for the coming school holidays.

Thanks to habitat loss, lack of food and a series of wet summers, butterflies and moths have suffered catastrophic declines in recent years, and we can do our bit to ensure their survival by creating refuges in our gardens. There are more than 50 butterfly and 2,400 moth species in the UK, and some of them will breed in your garden. But there's no need to worry: not all caterpillars have the fearsome appetite of the cabbage white, and many will complete their lifecycle in our gardens without us even noticing. Orange tip butterfly caterpillars, say, merely nibble at the edges of honesty seedheads, while little holes in flowers may reveal tiny tortrix moth larvae.

You probably already know that those caterpillars on your cabbages turn into cabbage whites, but what about those feeding on other plants? The best way to find out is to keep them as pets. While that may not be your idea of a good time, children will happily take up the challenge.

How to do it

Familiarise your children with the butterfly and moth lifecycle before sending them out to gather caterpillars. After mating, the female lays eggs on suitable plants, which hatch into larvae (caterpillars). Each larva then eats leaves before pupating into a pupa (chrysalis), from which the adult later breaks out.

Most egg laying occurs between spring and summer, though some species spend winter as a caterpillar or chrysalis, and complete their lifecycle the next spring. Any caterpillars you find at this time of year will probably do this, but if your children care properly for their pets between now and spring, and then watch the majestic emergence of a butterfly or moth, they'll be hooked on nature for life.

Send out your nature detectives with a notepad and container, encouraging them to look for chewed or rolled up leaves and flowers. The most exciting of all caterpillars is probably the elephant hawk-moth. Fuchsias are one of its favourite foods, so if you grow those, tell your children to inspect those plants first. Whatever caterpillars they find, encourage your children to handle their new pets with care, preferably transferring them from plant to container with a small net rather than by handling them directly (not least because some hairy ones can cause skin irritation). And get the children to note the plant on which they found their new charge, because they'll need to harvest leaves to feed it.

Keep larger caterpillars, such as elephant hawk-moths, in a large ice-cream tub or similar, while smaller ones can make do with a yoghurt pot or margarine tub. There's no need to add air holes, but lift the lid every other day to keep the air fresh, and replace the leaves every two days.

Put a layer of dry compost in the base, because some caterpillars will burrow into it when they pupate (larger ones will need a depth of at least 10cm) – don't be tempted to use garden soil because this may introduce centipedes, which will make a meal of your children's new friend. Stand a twig in the compost for the emerging adult to climb up and dry its wings, then gently pop the caterpillar in its new home, add a few leaves from the plant you found it on and close the lid.

Keep the container somewhere that's not too bright, dark, hot or cold – a windowsill or porch that's not in direct sunlight is ideal – and where it won't be forgotten. Or keep it outside, but out of the rain.

Encourage your children to record how much their caterpillar grows between now and autumn, and whether it changes colour. As autumn progresses, it will either stop eating and bed down in the foliage, or it will bury itself in the soil to pupate; butterflies, however, are likely to suspend their chrysalis from the twig. There's usually no need to feed overwintering caterpillars, though on mild days check that they're still dormant.

Then you just watch and wait. From early spring, check the container daily and, if you still have a caterpillar in there, regularly add fresh leaves. Once it has pupated, and after the adult has hatched, get the kids to release it where they found it, ready to start the next lifecycle.

Ten species to look out for

Angle shades moth; buff ermine moth; elephant hawk-moth; privet hawk-moth; lesser yellow underwing; orange tip butterfly; red admiral butterfly; ruby tiger moth; vapourer moth; white ermine moth.

Ten foodplants for moths and butterflies

Foxglove; fuchsia; holly; honesty; honeysuckle; hops; ivy; primrose; sweet rocket; verbascum.

For more information on butterflies and moths, visit the charity Butterfly Conservation