City Pets - Make a Butterfly Nursery

Gardeners will want you to gather caterpillars from their precious fruit plants or flowers, but your best bet is to go and dig up a nettle, 25cm (10in) high with roots the size of a tennis ball, for which you will need gardening gloves, a trowel and nerves of steel. But your caterpillars will thank you for it. Pot your nettle and tend it as well as you can - if it dies or they eat it all, replace it - to give your new pets the best diet possible.

Step Two

Gather five or six caterpillars from nettle patches. "You have to accept that there will be some casualties," says Martin Warren from Butterfly Conservation. Look for little, 1-2 cm, black fuzzy fellas and nudge them, without getting stung by nettles if possible, into a collecting box. Better still, harvest the nettle they are eating. The larvae, or caterpillar, of the common small tortoiseshell are black with yellow spots that merge into stripes and have spiky hairs on their backs, whose sole function is as a choking hazard for birds. Be thankful you are not searching for the Black Hairstreak, whose ingenious anti-avian strategy is to look like bird poo. These are rare and easily mistaken for something else.

Step Three

Cut the centre out of the lid and the bottom of a shoebox, and make windows with transparent plastic film, available from craft shops. Put in as many (small) airholes as the structural integrity of the shoebox can withstand. Place the potted nettle inside the box and secure the lid with an elastic band or two. Put the box somewhere light. Now you can watch your very own hungry caterpillars systematically stuffing themselves for a few weeks, possibly doubling their weight every two days, and also generating a surprising amount of poo - or "frass" - which may need to be cleaned out.

Then, one day, after they've reached a fat 4cm, they'll hang themselves upside down from the lid of the box for a few days, and go into the long sleep of the chrysalis. This is a sleeping bag made out of spit and their own, moulted skin. "If you look closely at the chrysalis you can see the outline of things like the legs and antennae," says Dr Caroline Boorman, a species ecologist from Butterfly Conservation. "In the later stages it's almost like an adult butterfly that has been shrink-wrapped." Get your children to draw the stages every day, to document the metamorphosis.

Step Four

After another two to three weeks, in the early morning between 6-9am, the adult butterflies will emerge, probably small tortoiseshells, peacocks or, if you're lucky, a red admiral. They flex their dry wings and may shed a liquid called meconium, which looks like blood, but is harmless waste. After a couple of days of wing-flexing, they can be rereleased into the wild, a Born Free project without the need for Land Rovers. Who knows, perhaps one day your children could become underpaid, under-appreciated entomologists, too?

Butterfly Conservation is having a national week during July 22-30

www.butterfly-conservation.org, www.ukbutterflies.co.uk

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