Coccinellidae is a family of beetles, known variously as ladybirds (British English, Australian English, South African English), ladybugs (North American English) or lady beetles (preferred by some scientists). Lesser-used names include ladyclock, lady cow, and lady fly.

They are small insects, ranging from 1 mm to 10 mm (0.04 to 0.4 inches), and are commonly yellow, orange, or scarlet with small black spots on their wing covers, with black legs, head and antennae. A very large number of species are mostly or entirely black, gray, or brown and may be difficult for non-entomologists to recognize as coccinellids (and, conversely, there are many small beetles that are easily mistaken as such, like tortoise beetles).

Coccinellids are found worldwide, with over 5,000 species described, more than 450 native to North America alone.

A few species are pests in North America and Europe, but they are generally considered useful insects as many species feed on aphids or scale insects, which are pests in gardens, agricultural fields, orchards, and similar places. The Mall of America, for instance, releases thousands of ladybugs into its indoor park as a natural means of pest control for its gardens.

Some people consider seeing them or having them land on one's body to be a sign of good luck to come - and that killing them presages bad luck.

Biology

Coccinellids are typically predators of Hemiptera such as aphids and scale insects, though conspecific larvae and eggs can also be important resources when alternative prey are scarce. Members of the subfamily Epilachninae are herbivores, and can be very destructive agricultural pests (e.g., the Mexican bean beetle). While predatory species are often used as biological control agents, introduced species of ladybirds (such as Harmonia axyridis or Coccinella septempunctata in North America) outcompete and displace native coccinellids and become pests in their own right.

Coccinellids are often brightly colored to ward away potential predators. This phenomenon is called aposematism and works because predators learn by experience to associate certain prey phenotypes with a bad taste (or worse). Mechanical stimulation (such as by predator attack) causes "reflex bleeding" in both larval and adult ladybird beetles, in which an alkaloid toxin is exuded through the joints of the exoskeleton, deterring feeding. Ladybugs, as well as other Coccinellids are known to spray a venomous toxin to certain mammals and other insects when threatened.