Scarlet beetles eat aphids—and sometimes crops
Coccinellidae, named in 1807 from Latin scarlet, covers ladybugs or ladybirds—oval, domed beetles from 0.8 to 18 millimeters. Most hunt aphids and scale insects; some chew plants or fungi. Farmers import them as biocontrol, though a few species become pests themselves.
More than 6,000 species are described worldwide. The English name began as Our Lady's birds: Mary was often painted in a red cloak, and the seven spots of Europe's commonest species were read as her seven joys and sorrows; Germans likewise say Marienkäfer. Entomologists prefer lady beetle, since these are beetles rather than true bugs. Bright red-and-black or yellow patterns, built from carotenes and melanins, mostly warn predators of a foul taste, though some aid camouflage, courtship or heat control.
Diet varies more than the reputation suggests. Scale insects seem to be the ancestral food; aphid-eating arose three separate times and leaf-eating twice. Aphid specialists make up about 68 percent of temperate species but only 20 percent worldwide, while roughly 36 percent of all species feed mostly on scale insects. Larvae and adults eat the same prey. A 2021 genetic study suggests the group arose about 143 million years ago and radiated in the Late Cretaceous as flowering plants multiplied aphids and their kin.
Mating is promiscuous. Males insert three sperm packets of about 14,000 sperm each although females can store only 18,000, probably a form of sperm competition. Females lay upright yellow eggs beside prey colonies, adding extra infertile eggs as a larder when food is scarce, and hatchlings often eat their siblings. Adults live up to a year and gather in clumps to hibernate. British studies clocked flights of up to 120 kilometres at 30 kilometres an hour, reaching nearly 1,100 metres.
Biocontrol introductions have had mixed results, and the invasive harlequin, Harmonia axyridis, threatens native species. The oldest fossils come from French amber about 53 million years old.
Source: Coccinellidae
