Coccinellidae is a family of beetles, known variously as ladybirds (UK, Ireland, Australia, Pakistan, South Africa, New Zealand, India, Malta, some parts of Canada and the US), or ladybugs (North America). Scientists increasingly prefer the names ladybird beetles or lady beetles as these insects are neither birds nor true bugs. Lesser-used names include ladyclock, lady cow, and lady fly.
Coccinellids 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 coccinellid species are mostly, or entirely, black, grey, or brown and may be difficult for non-entomologists to recognize as coccinellids. Conversely, there are many small beetles that are easily mistaken for coccinellids, such as the tortoise beetles.
Coccinellids are found worldwide, with over 5,000 species described, more than 450 native to North America alone.
A few species of ladybug are considered 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. Harmonia axyridis (or the Harlequin ladybug) was introduced into North America from Asia in 1988 to control aphids but is now the most common species as it is out-competing many of the native species. It has since spread to much of western Europe, reaching the UK in 2004.
A common myth is that the number of spots on the insects back indicates its age.
The nameladybird originated in Britain where the insects became known as Our Ladys bird or the Lady beetle. Mary (Our Lady) was often depicted wearing a red cloak in early paintings and the spots of the seven spot ladybird (the most common in Europe) were said to symbolise her seven joys and seven sorrows. Common names in other European languages have the same association (the German name Marienkfer translates to Marybeetleor, literally, Mary-chafer). In the United States the name was adapted to œladybug.
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 œreflex 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 toxin that is venomous to certain mammals and other insects when threatened.
Most coccinellids overwinter as adults, aggregating on the south sides of large objects such as trees or houses during the winter months, dispersing in response to increasing day length in the spring. In Harmonia axyridis, eggs hatch in 3-4 days from clutches numbering from a few to several dozen. Depending on resource availability, the larvae pass through four instars over 10-14 days, after which pupation occurs. After a teneral period of several days, the adults become reproductively active and are able to reproduce again, although they may become reproductively quiescent if eclosing late in the season. Total life span is 1-2 years on average.
It is thought that certain species of Coccinellids lay extra infertile eggs with the fertile eggs. These appear to provide a backup food source for the larvae when they hatch. The ratio of infertile to fertile eggs increases with scarcity of food at the time of egg laying.