Q What are lily beetles?

A Lily beetles (Lilioceris lilii) are attractive, bright-red beetles around 7mm long with black heads, legs and undersides. They can deter predators by squeaking – they are audible if you hold them close to your ear.

Caption: Lily beetles sometimes drop off the plant as you approach

Q Which plants do lily beetles attack?

A Adults and larvae eat the leaves, flowers and seed pods of lilies, fritillaries and nomocharis and can do severe damage. Adult beetles nibble irregular holes in the leaves and petals, while the larvae methodically work their way from the leaf tips towards the stem. Adults are occasionally found on other plants, including Solomon’s seal and lily-of-the-valley, but these plants do not seem to be eaten by the larvae. 

Q Tell me about their life cycle.

A The adults overwinter in the soil or on leaf debris and can appear from late March if the weather is warm. After mating, the female lays 200-300 orange eggs on suitable plants. About a week later, these hatch into reddish-brown larvae that cover themselves with their own black, slimy excrement. When the grubs are mature, they burrow into the soil to pupate, emerging as adults in mid- to late-summer.

Q Could I confuse them with anything else?

A Cardinal beetles are also bright red, with black legs, head and undersides. However, they are twice as big as lily beetles and the body tapers towards the head. Cardinal beetles are carnivorous, hunting other insects on a wide range of plants, especially tree trunks. Some soldier beetles are reddish-brown, and the same colour underneath. They tend to favour flat, open flowerheads such as umbellifers and are often seen in mating pairs. They are also carnivorous.

Q Where does the lily beetle come from?

A It originated in the Mediterranean region, though it also occurs in China and northern India. Lily beetle was recorded in England in the early 1900s. However, it did not become successfully established until 1940, when it gained a foothold in a private garden in Cobham, Surrey.

Q How far has it spread?

A Lily beetle has now spread across the whole of the UK, but populations are more common in the south.

Q How can I control lily beetle?

A If you grow only a few lilies, it’s feasible to control lily beetle by inspecting them regularly. Pick off and squash the adults, grubs and eggs; the earlier you start looking, the more likely you are to break the pest’s life cycle. Keep the beetles under control, at least until the plants finish flowering, to allow the bulbs to build up enough to form next year’s flowers. Where plants have been badly damaged, feed the remaining leaves with foliar feed.

Q Are there any suitable sprays?

A If you have lots of lilies and wish to spray them, use Westland Resolva. If plants are flowering, spray at dusk to avoid harming bees. The grubs are more susceptible than the adults, which are protected by their hard coats.

Q What about biological control?

A The lily beetle’s warning red colour implies it is unpalatable to potential predators such as birds. However, scientists from the University of Rhode Island, USA, motivated by the recent arrival of the pest in Boston, found parasitic larvae on lily-beetle grubs in France. It is hoped they may prove to be an effective biological control in future.