The lily beetle is an insect known scientifically as Lilioceris lilli that feeds on lily plants, lays its eggs on lily bulbs, and is known throughout Europe and the Northeastern United States as a formidable garden pest. These beetles have a bright red color, which makes them easy to identify. They are nevertheless very hard to kill and eradicate. Female lily beetles can lay upwards of 400 eggs at a time, and once these hatch armies of plant eaters can make short work of a garden in as little as a few days.
Lily beetles will eat many different kinds of plants and types of lilies, but favor — and will only lay their eggs under — plants that fall within the Lilium species. Tiger lilies, Easter lilies, and Oriental lilies are all examples. Beetles usually start by eating the lily leaves, but will also destroy bulbs, roots, and blooms until there is little left but detritus.
Western European gardeners are believed to have introduced the lily beetle to North America in the mid-1940s, probably in a contaminated bulb shipment. The beetles were first noticed in the Canadian province of Quebec in 1945. They remained contained there for some time, but were documented in the Northeastern United States in the early 1990s. The beetle is a strong flier and can travel great distances in search of food, but scholars suspect that the insect came into the United States through human-instigated transportation of bulbs, garden supplies, or farming merchandise.
Lily beetles are characteristically a vibrant red color, and can range in size from a ½ to ¼ inch (anywhere from 6 to 13 mm). Adults often travel in pairs, establishing massive families on the undersides of lily leaves and on the casings of lily bulbs. Mature lily beetles do cause some leaf destruction, but their primary focus is usually propagation.
A female lily beetle can usually lay between 200 and 400 eggs at a time, several times a season. These eggs, which are also bright red, hatch in a staggered fashion. Hundreds of larvae often emerge at once, and begin feeding almost immediately.
Larvae are often far more destructive than their parents. They feed in groups, and are capable of devouring entire leaves and stalks in very short periods of time. As they grow, developing beetles typically hide from predators by covering themselves in their own excrement, and move together as a pack.
It is often very difficult to kill the lily beetle. Most beetles are largely temperature resistant, and can hang onto bulbs throughout the winter in most places. When they feel threatened, they move quickly, and are often slippery and resistant to squishing and capture in any event.
Some pesticides, particularly those derived from the Southeast Asian Neem tree, have proven effective against the lily beetle. A host of commercial insecticides also target friendly bugs, and many can be damaging to the delicate lily plant, as well. In most cases, the best way to eradicate the insect is to target its egg sacs. Gardeners who can destroy eggs before they hatch have a much better chance of limiting the lily beetle infestation, though this often requires near-constant monitoring. In most places, part of caring for lilies is routinely checking for the arrival of these lily pests.