The harlequin ladybird is a voracious aphid predator. Harlequin ladybird larvae can consume as many as 90 to 370 aphids during their larval period, while adults typically eat up to 65 a day (3) (5), equating to over 5,000 in their adult lifetime (3). Females usually eat more aphids than males (5). In addition to aphids, the harlequin ladybird also eats a range of other insects, including scale insects, the eggs and larvae of butterflies and moths, and even other ladybirds. Pollen, nectar, fruit juices and honeydew are also consumed (4) (5).
The bright colours of this and other ladybirds serve to warn potential predators that they are distasteful. If attacked, the harlequin ladybird secretes a yellowish substance known as ‘reflex blood’, which contains distasteful toxins and smells unpleasant. However, despite these defences, harlequin ladybirds may be predated by some birds, spiders, predatory insects and even bats, and their eggs and larvae may be eaten by other ladybirds (3) (4) (5) (7) (8). This species is also parasitised by the larvae of some wasps and flies (2) (3) (4) (7) (8). The harlequin ladybird can be cannibalistic, eating members of its own species when other prey is scarce, but individuals appear to recognise their close relatives and are less likely to cannibalise a sibling than a non-sibling (3) (5).
As in other ladybirds, the life cycle of the harlequin ladybird involves an egg, larval, pupal and adult stage (3) (4) (5). Each female harlequin ladybird can produce around 1,000 to 2,000 or so eggs in its lifetime (4) (5) (9) (10), usually laying them in batches of about 10 to 30 per day (5) (9). The eggs of this species are oval-shaped and are pale yellow when laid, later turning darker yellow before becoming grey-black just before hatching (3) (5).
The time taken for the harlequin ladybird’s eggs and larvae to develop depends on a number of factors, including temperature and diet. In temperate regions, the eggs usually hatch after around four to five days and the larvae take about three weeks to develop (2) (3), shedding their skins four times during this period (4) (7). The harlequin ladybird’s pupal stage lasts about one week (2) (3) (4).
In its introduced range in the United Kingdom, the harlequin ladybird is reported to lay the majority of its eggs in June and July, with the adults emerging from the pupae in August (7). After feeding on plenty of aphids to see them through the winter months (4), the adults of this species spend the winter in a dormant state, often overwintering in large aggregations in dark, concealed locations, including buildings (2) (3) (4) (5) (7). Harlequin ladybirds usually migrate to their overwintering sites from around September to November (3) (5). As this period coincides with Halloween, this species is also sometimes known as the ‘Halloween ladybird’ in the United States (4) (5).
As temperatures warm up in the spring, the adult harlequin ladybirds become active again and leave their overwintering sites to search for food and to mate (3) (4) (5) (7). The adult harlequin ladybird usually lives for about a year, and is reproductively active for around three months of this (2) (3). Unlike many other ladybird species, which require a period of winter dormancy before they can breed and have only one generation each year, the harlequin ladybird often has two generations in a year (2) (3) (5). In some areas with longer warm seasons, it may even have as many as four or five generations (3) (5).