The Lily Beetle (Lilioceris lilii) is native to mainland Europe and Asia, but not the British Isles. It was first reported in Southern England in the nineteenth century but it is believed that they did not become established until the 1940s. They had been confined to the south, but the recent increase in average temperatures has allowed them to move northward. The first reported find in Northern Ireland was in a garden in Belfast in June 2002. They have also moved to North America, first reported in Canada in 1945 and now spreading south in the eastern states of USA.
The bright red body, black legs and head make Red Lily Beetles very striking in appearance, but these 6-8mm long beasts are very destructive to bulbous plants and in particular Lilium such as Turk's cap lilies, Asiatic lilies, Oriental lilies, Tiger lilies, Solomon's Seal and Fritillaries.
Lily Beetles Mating
From spring to autumn the beetles and larvae feed on the foliage, flowers and stems. The removal of the leaves deprives the plant of food production which severely weakens it and may prevent flowering the following year, or in severe cases kill the plant. Although I haven't seen it mentioned on websites the biggest problem they seem to cause me is that they eat through the base of the stems themselves and kill the whole stem (though it may be that snails or slugs are doing this).
Between April and September the beetles lay eggs on the undersides of leaves. After a week they hatch into reddish-brown maggot-like grubs that feed on the same parts of the plant as the parents. To deter predators or disguise themselves, the larvae cover themselves in their own wet, black excrement.
There are various chemical solutions but I am not in favour of those. The 'greener' way is to pick off the grubs and adults as soon as you see them. The adults will drop to the ground at the slightest touch, so spread newspaper under the plants to catch them. Be quick or they'll fly off. Unfortunately you are then left with the problem of disposing of them. I am loathe to kill things so I tend to drop the whole lot in the garden bin with some of the damaged lily leaves and let the fates decide their future.