Adalia bipunctata (Linnaeus, 1758)
This is a native Nearctic and Palaearctic species with a Holarctic distribution which occurs in many other areas e.g. Australia and Hawaii either through accidental introduction or through deliberate use as biocontrol agent. It was formerly common throughout most of its range but there has been a recent and often drastic decline e.g. it was the second most common ladybird in the United States but is now local and rare in many areas, it remains locally common through Europe including the U.K. but nonetheless the decline has been drastic in many areas. This decline may be due to competition with the invasive Harlequin Ladybird, a species known to predate the 2-spot and which has increased alongside the decline of that species. Both adult and larvae 2-spot are voracious aphidophages and the adults are very fecund, hence their suitability as biocontrol agents on a wide range of crops worldwide e.g. cotton, peach, potato, beans etc. In temperate regions the adults appear in March and are soon common; they generally inhabit low vegetation e.g. nettles and docks in just about any situation where the prey occur, and during warm weather they appear on umbel flowers and blossom etc. and may be beaten from almost any vegetation although they are generally less arboreal than the 10-spot. Mating occurs during May and June and oviposition continues over several weeks during June and July; the cylindrical yellow eggs are laid in batches of 10-40 on the underside of leaves etc. where aphids occur and hatch within a week or so. Under ideal conditions each female may lay up to 500 eggs. Newly hatched larvae consume part of the chorion before moving in search of aphids and their nymphs and eggs and at this stage they may be seen on the backs of adult aphids feeding upon the body fluids as they move. Older larvae are very mobile and will cover whole plants or move between plants in search of prey. There are four instars and it is thought that on average more than 250 aphids are consumed during larval development. Pupation occurs from late June to August, generally under leaves but also on fences or posts etc. and the adults eclose after a week or so thus producing an autumn abundance; they feed through late summer and autumn before overwintering although in good years there may be a partial second generation. Adults are long-lived and there are records of individuals overwintering a second time. On the continent and in the U.S. there are usually 2 generations and often 3. Winter is passed under bark or among debris or leaf-litter on the ground and they are well-known for overwintering in sheds and houses; they often overwinter in large groups along with other common species. Freshly eclosed adults are plain ochreous and lack any pattern, this develops over a few days but more subtle changes occur over the following weeks and months so that specimens seen in the early spring are often a striking deep red.
3.5-5.5mm. Habitus broadly rounded, moderately convex and glabrous. Colour variable but the underside and legs are completely black, and the mouthparts and antennae are brown. The head is entirely black or black with 2 pale spots. The pronotum is white with black spots or lines loosely in the shape of an M. The typical form is red or orange with a black spot at the centre of each elytron. Melanic forms include quadrimaculata which has black elytra with two pairs of pale or red macula and sexpustulata which is black with 3 pairs of red marks. The anterior macula in these melanic forms varies and may be angled, continuing along the lateral margin, or large; covering the humerus and continued to the scutellum. In extreme cases the black ground colour is reduced to a transverse band across the middle and dark marks towards the apex. Other forms exist but they are rare in Europe and Asia, the widest variation in colour occurs in the United States with mature spotless forms, 4-banded red forms and 9-12 spotted red forms. The femoral lines are circular but do not form a complete semi-circle. Claws smooth with a large basal tooth.