The scarlet lily beetle, red lily beetle or lily leaf beetle is a beetle from the leaf beetle family (Chrysomelidae). The scientific name for this beetle is Lilioceris lilii. This beetle and its larvae live on various species of lilies (hence its name) but also on the crown imperial (Fritillaria imperialis) and other members of the Liliaceae family. In my garden the lily beetles even seem to prefer the crown imperial.
The scarlet lily beetle overwinters in the soil or in a tree stump as an adult beetle. In April they emerge from their hiding place to feed and mate. They lay their eggs on the underside of leaves and 1 or 2 weeks later they hatch. After about 2 to 3 weeks later the larvae are fully grown. They pupate in the ground and about 2 to 3 weeks later the adult emerges.
The damage these beetles do is nothing compared to the disastrous effect their larvae have. The larvae look more like a blob of mud or bird dropping because they cover themselves with their own slimy excrements. I have never encountered such devastating blobs as these. If they can they will start eating at the growing point of the lily and that is where the flowers develop. Some of the years I have flowerless lilies because of this. I do not have lily beetles in my garden every year. Because of that I am not always as alert and I have to pay with flowerless lilies.
The red lily beetle can be seen from April till August. They are easy to spot because of their red color. As soon as they sense/see motion they let themselves drop on their back. Their undersurface is black which makes them hard to spot on the black ground. If you want to catch them you have to be careful and quick. I crush the beetles and larvae because I do not want to use chemicals.
Because the beetles taste nasty and the larvae resemble droppings, birds do not eat them. There are some parasitic wasps in Europe (e.g.: Tetrastichus setifer, Diaparsis jucunda and Lemophagus errabundus) that lay their eggs in the larvae. Those eggs hatch and kill their host. The Tetrastichus setifer was successfully released in North America as part of a biological control program. Also Diaparsis jucunda and Lemophagus errabundus have been released. But even with these parasitoids not all the red lily beetles will be killed. The conclusion is that you have to rely mostly on your own handpicking for the control of the red lily beetle in your garden.
Parasitoids overwinter in the soil in the immediate vicinity of the bulbs. It is therefore better not to remove the bulbs or plough the soil around the bulbs.