This pretty little beetle, Liliocertis lilii - with its bright scarlet body and black underside - can be a nightmare to any gardener growing lilies or fritillaria.

A native to Europe, the lily beetle made its debut in Montreal, Canada in 1945 - finally reaching the USA in 1992. It is believed the beetles found their way into some bulbs that were imported from mainland Europe. The same is thought to have happened in the UK, where the beetle is now thriving and becoming a real garden pest.

The adult beetles, which grow up to 9mm, appear in spring. They will taste most members of the lily family including - Solomon's seal and bluebell, but their preferred food is species lilies and fritillaria. These are also the plants on which they choose to lay their eggs. The eggs are laid on the underside of leaves in a line; they are orange in colour and hatch from between a week and ten days later. A female can lay up to 450 eggs in her lifetime of two seasons.

The larvae look like small slugs and come in a wide range of colours: orange, brown, yellow or green with a black head. It's not recommended that you touch the larvae with bare hands, as they cover their backs with their own excrement in order to deter any predators. The excrement is not toxic, but is just very unpleasant. The larvae will do the most damage to your lilies, feeding for 16 - 24 days before pupating underground.

The pupae are bright orange in colour; 22 days later the new adult will emerge. They overwinter¹ in the ground or under dead leaves, sheltered from the cold weather until spring. Then the cycle of mating and breeding begins again.

In France and Switzerland the beetle has been brought under control by four species of parasitic insects which attack the eggs and larvae. One of these European species has already been released in Boston, USA with good results. Experiments are being conducted at the Plant and Sciences Department of Rhode Island University, on other 'host-specific' insects - hopefully leading to a further release in the USA.

What do I do if I find them on my Lilies?

The best way to deal with these beetles is to pick them off and dispose of them. (No! Not into your neighbours garden!) Remember, they can lay a lot of eggs, which will come back as adults and eat your lilies. The beetles are harmless and don't bite - though they do emit a squeaking sound if you hold them firmly. As a defence, if disturbed, the beetle will drop to the ground belly-side-up, so it cannot be seen. When all danger has passed, it will climb back onto the plant. Squash any eggs you find and wear protective gloves to pick off any larvae. If you cannot bring yourself to touch the beetles, try using a garlic barrier spray to help prevent them from feeding and breeding on your plants. They can also be treated with insecticides available at garden centres.