Invertebrates
Ladybug
Coccinella septempunctata · also called ladybug, ladybird, seven-spot ladybird
The ladybug, or ladybird, is one of the few insects almost everyone likes — a small, glossy, dome-shaped beetle in cheerful red and black. The bright colours are not for decoration; they warn that the beetle tastes foul, and if the warning is ignored it can bleed a drop of bitter fluid from its own knees. Both the adult and its spiky larva spend their lives eating aphids, which is why farmers have prized them for hundreds of years.
Overview
There are about 6,000 ladybird species worldwide, in almost every habitat outside the poles. They are 1–10 mm long, strongly domed, most often red, orange, or yellow with black spots. They eat mainly aphids, scale insects, and mites, and a few species eat plants or mildew instead.
Warning colours and reflex bleeding
The bold pattern advertises that the beetle is distasteful and mildly toxic. Threatened, a ladybird releases a drop of foul, bitter yellow fluid from its leg joints — reflex bleeding — laced with alkaloids that deter ants, birds, and spiders.
Winter clusters
Many ladybirds overwinter packed together in large groups under bark, in crevices, or in buildings, guided back to the same spots by a lingering aggregation scent.
A name from folklore
The name is often traced to medieval farmers who prayed to Our Lady for relief from aphids and named the helpful beetles after her.
Not all are helpful
The harlequin ladybird, spread worldwide as a biocontrol agent, has become a damaging invader that eats native ladybirds, swarms into houses, and taints wine. Several native ladybird species have declined sharply as a result.
Status
Most ladybirds are Least Concern, but several native species are declining, linked to the harlequin, pesticides, and habitat loss. The number of spots does not indicate age.
Ladybug: common questions
Can you tell a ladybug's age from its spots?
No. This is one of the most persistent insect myths. The number of spots on a ladybird is fixed by its species and does not change over its life; a seven-spot ladybird has seven spots as a newly emerged adult and seven spots when it dies. What can happen is that a freshly emerged ladybird is pale, sometimes yellow or orange, with faint spots, and darkens to its full colour and contrast over the first day or two, which may be where the idea of spots appearing with age comes from. Ladybirds live for roughly a year, and most of that is spent as a larva, pupa, or overwintering adult.
Do ladybugs bite, and is the yellow liquid dangerous?
Most ladybirds cannot bite a person meaningfully, but a few larger species, notably the invasive harlequin ladybird, can give a small nip that feels like a pinprick and occasionally raises a tiny welt. The yellow fluid released from the leg joints when a ladybird is handled or alarmed is its defensive reflex blood; it stains, smells unpleasant, and tastes bitter, and it can cause mild irritation if it gets into the eyes or a cut, but it is not toxic to humans and washes off.
Why do ladybirds come into houses in autumn?
They are looking for somewhere sheltered and stable to spend the winter. In the wild many ladybirds overwinter in tight clusters under loose bark, in leaf litter, or in rock crevices, and a warm, dry, still building offers the same thing. This is mostly a habit of the harlequin ladybird, which gathers on and inside walls, window frames, and lofts in large numbers, following scent trails laid by earlier arrivals. The beetles are harmless indoors, do not breed or feed there, and can be gently swept up and put outside in a cool sheltered spot, though disturbing them triggers the smelly reflex bleeding.
How are ladybirds used to control pests?
Because they eat aphids in large numbers, ladybirds have been deliberately used in agriculture and horticulture for well over a century. One of the earliest and most famous cases was the introduction of an Australian ladybird to California in the 1880s, which rescued the citrus industry from a scale insect. Today ladybirds are reared commercially and released in greenhouses and gardens against aphid outbreaks. The approach has to be used carefully, since released beetles may fly away, may not arrive in time, and, as the harlequin ladybird showed, an introduced species can turn into a bigger problem than the pest it was meant to solve.