What Do Ladybugs Eat? Aphids, Scale Insects, Pollen and Mildew

Why are aphids the main food of ladybugs?

Aphids are soft, slow and extremely common. In spring and early summer their colonies grow explosively on young shoots, offering an easy meal for any predator that can find them. Ladybugs that hunt aphids lay their eggs right next to these colonies, so the larvae hatch surrounded by food.

In ladybirds, larvae and adults usually eat the same food. The seven-spot ladybug, Europe’s most familiar species, eats at least 24 kinds of aphid and needs them to grow and to produce eggs. Ladybugs find aphid colonies partly by smell. Aphids under attack release an alarm scent, and many plants give off chemicals when aphids feed on them, both of which attract hungry ladybirds.

Not every aphid is a safe meal. The lupin aphid takes up bitter compounds from lupin plants and can harm seven-spot ladybirds that eat it. Aphids also have bodyguards: many ants “farm” aphids for their sugary honeydew and attack ladybugs that come close, as wood ants do in European forests, described in the red wood ant profile.

Aphid-eaters dominate in cooler regions, making up roughly two-thirds of ladybird species in temperate areas. Worldwide, though, only about one in five ladybird species mainly eats aphids.

How many aphids does a ladybug eat?

A ladybug larva is a fast-growing eating machine. Over the two or three weeks before it pupates, a typical aphid-eating larva eats hundreds of aphids, and an adult keeps hunting for months. In the convergent lady beetle of North America, a fully grown larva may eat about 50 aphids a day and an adult about 20.

The numbers vary widely. Ladybugs eat more in warm weather, when their bodies work faster, and larger species eat more than small ones. Females need extra food to make eggs. In lean times, when aphids are scarce, they can survive for a while on other foods.

Ladybugs that eat scale insects, mealybugs and mites

Around a third of all ladybird species feed mainly on scale insects, small sap-sucking relatives of aphids that live under waxy or armored coverings on stems and leaves. Studies of ladybird family trees suggest scale insects were probably the original food of the group, with aphid-eating evolving later.

The most famous scale-eater is the vedalia beetle (Novius cardinalis) from Australia. In the late 1880s it was brought to California to fight the cottony cushion scale that was devastating citrus orchards. It brought the pest under control within a few years and is still described as a textbook example of successful biological control. The beetle was later used with similar success in 29 countries.

Other specialists include the mealybug destroyer (Cryptolaemus montrouzieri), whose larvae are covered in white wax and look like the mealybugs they eat, and the tiny black Stethorus ladybirds, which hunt spider mites.

Ladybugs that eat mildew or leaves

A few ladybirds do not hunt animals at all. The bright yellow 22-spot ladybird and the orange ladybird of Europe graze on powdery mildew, a fungus that coats the leaves of many plants. Their whole tribe, the Halyziini, depends on fungi.

Members of the subfamily Epilachninae are plant-eaters. The Mexican bean beetle chews the leaves of beans and is a crop pest in parts of North America, and its relative the squash beetle feeds on squash and pumpkin leaves. In Europe, the small 24-spot ladybird feeds on the leaves of herbaceous plants. These plant-eating ladybirds are often slightly hairy and have a matt look.

Pollen, nectar, honeydew and fruit

Even meat-eating ladybugs are not strict carnivores. When aphids are scarce, seven-spot ladybirds eat pollen, nectar, honeydew, fungal spores and small insects such as thrips and whiteflies. These foods keep them alive, but they are not enough to produce eggs.

Late in the year, seven-spots feed on pollen from flowers of the daisy and carrot families to build up fat for the winter. In early spring, when they wake up, they visit early-flowering shrubs such as blackthorn for nectar. The harlequin ladybird goes further and eats soft fruit such as grapes and raspberries in autumn.

Do ladybugs eat each other?

Yes, especially when food is short. A newly hatched larva first eats its eggshell and often any unhatched eggs nearby. Some ladybirds lay extra infertile eggs among the fertile ones, and these act as a packed lunch for the larvae. Females lay more of them when food is scarce.

Larvae and adults also eat the eggs, larvae and pupae of other ladybird species. This is called intraguild predation, and it is one way the invasive harlequin ladybird pushes out native species in Europe and North America.

Why do gardeners and farmers welcome ladybugs?

Aphids, scale insects and mites suck plant sap, weaken crops and can spread plant viruses. Wild ladybugs are among the most important natural predators of these insects, which is why gardeners and farmers count them as beneficial insects and why ladybug numbers often rise right after an aphid boom.

Deliberate introductions have a mixed record. Scale-eating species such as the vedalia beetle have worked well because they are specialists. Aphid-eaters are less predictable: by 2000, only one of 155 recorded introductions of ladybirds against aphids was judged substantially successful. Aphid-eating ladybirds are mobile generalists that move on when aphids run short, which makes their impact hard to steer. Their bright colors still warn birds that they taste bad, as explained in are ladybugs poisonous?