Pests and diseases - Caterpillars

Signs - Leaves stripped, or eaten from the outside edge inwards. May not always be easily visible as they can be well camouflaged. "Frass" may be seen, tiny black balls of excrement. More cunning and smaller types "mine" leaves between the upper and lower surfaces, others build a dense web of silk to protect a small colony that feeds on the plant within the web.

Damage - Young leaves can be eaten away and more mature plants are left with unsightly holes.

Treatment - Leave them for the birds or pick off caterpillars by hand as soon as you see them. If you can't bring yourself to kill them, I move them from where they usually are on the young delicate succulent leaves at the top of the plant to the larger more mature leaves elsewhere. This however becomes a daily job as they climb back again!

For really heavy infestations consider using the biological control based on a naturally occurring bacterium called Bacillus thuringiensis, which stops the caterpillar feeding and only infects caterpillars.

Pyrethrum, Malathion and Derris can be used to deal with heavy infestations.

    Elder spray.  This kills aphids, small caterpillars and is useful as a fungicide for mildew and blackspot on roses. The toxic agent is hydro-cyanic acid, so in preparing the spray use an old saucepan.

Gather 450g (1 lb) leaves and young stems of elder prefer-ably in spring when the sap is rising. Place in the saucepan and add 3.3 litres (6pt) water. Boil for half an hour, topping up as necessary. Strain through old tights and use the liquid cold and undiluted. It will keep for three months if bottled tightly while still hot.

Reasons to like caterpillars

Refer to any small child of your acquaintance for a comprehensive answer.

They turn into butterflies and moths "flying flowers".

They provide loads and loads of food for small birds and plenty of larger animals further up the food chain too.

They move in the most unlikely manner, a bit like a mini version of one of those Chinese Dragons they have in street parades where you're sort of taken in but at the same time, you know there's just a load on people underneath and the co-ordination could go at any time. Now imagine one of those dragons where the person in the middle desperately needs the toilet and they all have to hurry - that's a caterpillar. (not including the inchworm types) They have provided the inspiration for many cartoon and children's story book characters not to mention that great musical masterpiece "Inchworm, inchworm, measuring the marigolds..."