Garden Pests - Lily Beetles | Gardening Teacher Consultant

Lily beetles (Lilioceris lilii) are not native to the UK, but have now become widespread across most of the country.

As garden pests, the beetles are stunning to look at! They have a bright red wing case and black legs. But they are greedy pests. Whilst they may eat other plants in your garden, their preferred diet is Lilies and Fritillaries. And it is on these two plants that they will lay their eggs. However, not all the plants we commonly call lilies are affected, and there may be some plants which you didn’t know were susceptible – so we have a list to help you.

Home Sweet Home

Lilioceris lilii are originally from Asia. From the 19^th century, their range spread, probably helped by the increasing market for plants in Europe. First discovered in the UK in 1839, a colony wasn’t established here (in Surrey to be precise) until the Second World War.

The spread really began in the 1970s and it is now firmly established in much of the country as a horticultural pest. Elsewhere, it was first discovered in Quebec in 1943 and Massachusetts in 1992, and has of course, spread since then.

Plants affected by Lily Beetles

One thing to remember is that Lily beetles, as adults, will eat various plants Understandably, this has led to some confusion amongst gardeners, but does prove the usefulness of Botanical Latin for working out if a plant will be a host for the eggs.

host plants

The female adults only lay eggs on members of the Liliaceae family, specifically, Lilium aka “true lilies”, Fritillaria and Cardiocrinum.

Lilium includes both the species lilies and hybrids, which are those frequently grown in our gardens. Recent research suggests that some of the species lilies may be less susceptible to beetle attack, but findings are not yet conclusive (May 2023).

Lily host plants, for example –

Asiatic
Martagon, turks cap
Native American lilies
Oriental hybrids

Fritillaria host plants, for example –

Crown imperial
Fritillaria persica
Snakes head fritillary

Breakfast, lunch, afternoon tea….

The following list is not definitive, nor can I confirm all of the plants as being beetle food through my own empirical evidence. One thing to remember is that just because you see a Lily on a plant doesn’t mean to say its been feeding. For example, the damage may be due to slugs.

Arum lily, Zantedeschia aethiopica, Calla lily
Cardiocrinum giganteum, the giant Himalayan lily
Hemerocallis, day lily
Nicotiana, tobacco plants
Polygonatum, Solomon’s Seal
Solanum
Tricyrtis hirta, toad lily
Tulipa

When and Where in the garden to look for Lily Beetles

Unfortunately, the beetles may have overwintered anywhere in the garden, where they hibernate in the top couple of inches of soil or leaf debris. Although they’re unlikely to hole-up next to a host plant, it is worth checking the soil around your Lilies and Fritillaries anyway, in case some adults are on the move early.

Depending on the coldness of spring and the winter preceding it, the timing of adult beetles emerging may be delayed. The adults are looking for host plants, so they can lay eggs under the leaves. Egg-laying occurs from spring through to mid-summer. In other words, keep on looking!

Lily beetle eggs are orange, sausage-shaped and are laid on the undersides of leaves of the host plants.

The larvae are not so visually obvious as they’re a reddish brown with black head. But you’re more likely to spot their frass (insect poop) as they hide under this.

Signs of Lily beetle damage

Adults will feed on petals and seed pods, and leave round holes in leaves.

Whitish dried patches on leaves and leaves totally eaten away may suggest that larvae are present. They will also eat stems, petals and seed pods of the host plants.

And the really annoying thing? Once plants have been chomped and have eggs laid on them, they give off a smell which attracts other passing lily beetles!

How to prevent Lily Beetles from eating your Lilies and Fritillaries

Needless to say, we are only considering organic methods, so as not to harm any beneficial beasties (or indeed our pets).

Dealing with the beetles when you find them

This is likely to be your response if you haven’t had the beetles in your garden before and didn’t know to lookout for them. Or perhaps you were away / busy when they started munching your plants.

Options are

pick off by hand
spray
predatory wildlife

Picking off the beetles by hand

Manual removal can be sub-divided into pick & squish and pick & drown.

If you only have a few Lily Beetles in your garden, the easiest form of control is to pick the adults off and squish them with your boot or trowel. NB: The adults have a tendency to slip from your grasp and lie upside down and inconspicuous. Get around this by cupping one hand below, or laying newspaper on the ground.

When you find quite a few adults and larvae, this is a less yucky variation for removing them. Carry with you a bucket containing one of insecticidal soap; water & washing up liquid; crushed garlic or vinegar in water; cold black coffee. Or plain water, as the point is to drown the beetles by picking them off the plant and dropping them in the wet stuff.

I have two comments on the liquids. Firstly, keep the vinegar well away from your plants. Secondly, I haven’t tried out all the liquid options and have relied on other gardeners’ comments and experiences.

Spray

Sprays or drenches can be applied both to the host plants themselves and to the surrounding soil. The latter being more useful when the plants are potted rather than in the borders. Because of their hard insect carapace or exoskeleton, spraying directly onto the adults has little effect. And the larvae cover themselves as a protective measure.

The basic purpose of foliar and soil sprays is to make the host plants taste wrong, thereby depriving the larvae in particular of their food source.

There are organic sprays available to purchase, such as Grazers G4, garlic, herb and sunflower oil based ones. I have to say I like the squirt action of the Grazers bottle as it works upside down so you can treat the underside of the leaves more easily.

Predatory wildlife

Encouraging wildlife in the garden is not only encouraging biodiversity but also setting up your allies in the garden pest war. Whilst I haven’t seen birds eating the Lily beetle larvae, there are predatory ground beetles who will eat the larvae and sometimes the adult beetles too.

There are three species of parasitoid wasp known to occur in Britain that feed on the larvae of lily beetle. These are Lemophagus errabundus, Tetrastichus setifer and Mesochorus lilioceriphilus. Trials have been carried out in Canada and the USA to discover if they are a suitable biological control to introduce – so far it seems to work.

Preventing Lily Beetles

If you grow your lilies in pots, then I’d recommend repotting them annually into fresh soil. It may seem yet another chore, but also allows you to check that the bulbs are healthy and for vine weevils.

Using organic foliar sprays to reduce the tastiness of the foliage of host plants is best begun when you spot leaves emerging.

Remember to check the underside of the leaves of the Lily or Fritillary plant on which you found the beetle and remove any eggs as well. Although Lily beetles currently only produce one generation per year in the UK, they don’t all lay eggs at the same time, so checking throughout spring and summer is essential.

And lastly but most definitely not least, we are back to encouraging a good range of insect, animal and plant species into your garden.

Encouraging natural predators does mean that they will need a food source. Where they eat more than one type of pest that’s rarely an issue. But living with some damaged fritillaries and lilies whilst not having to do anything yourself about keeping the Lily beetles in check sounds like a good pay-off to me. Or am I just lazy …?

and finally, for more tips, advice and inspiration …

For more gardening help and ideas, check out Plews Potting Shed blogs, including the selection below. The blog has been going for over 10 years, so there are plenty of gardening topics to ‘scratch your gardening itch’

If you’d like Plews to help you with fighting Lily Beetles and other garden pests or perhaps want a planting design made of less tasty plants do get in touch.

More ideas and gardening advice can also be found in our monthly Tipsheet . You could come and find us on Instagram – @plewsgd Pinterest and Facebook too.

And on that note, you can have a peek at my (new, overgrown) garden at Spitfires and Slow Worms Instagram & Facebook

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