Adalia bipunctata (Linnaeus, 1758)
An abundant species throughout the British Isles although becoming rare in the north of Scotland. This certainly applies to Watford where the species is found everywhere. The largest numbers seem to occur in late summer on trees, especially Acer, Fagus and Quercus although beating just about any vegetation will produce them. They often overwinter in groups, sometimes with other species e.g. 7-spot (Coccinella 7-punctata L.), 14-spot (Propylea 14-punctata (L.)) and sometimes in large numbers, these groups often under bark. Single specimens commonly overwinter inside or around buildings, especially around window frames or behind fencing rails. Adults are active during the first warm days of March and by April, weather permitting, are found everywhere. They mate in mid or late spring and eggs are laid over a protracted period, perhaps a few weeks, during May and June. They are laid in batches of 20 to 50 and each female will lay several hundred. Eggs take a few days to hatch and larvae are seen until mid August when they pupate. Adults hatch within a week or two and become abundant in late summer. This is a generalisation and the whole cycle depends on temperature and food supply Majerus, in favourable years there is a partial second generation with adults from both cycles overwintering, there are records of bipunctata surviving a second winter. The adult pattern and colour develops over the day or two following emergence but more subtle colour changes take place over weeks or months so that newly active adults are often a rich deep red colour and very striking.

4.5-5.5mm. Glabrous, elytra characteristically shaped. Legs and underside of abdomen black (cf.Adalia 10-punctata (L.)). Antennae brown, at least basal segments, with club darkened. Very variable indeed with many (in general, pointlessly) named forms. In practice the species varies from almost black to almost red, but there are diagnostic features. When the elytral ground colour is red there may be a scutellar spot common to both but this is never bordered with white marks. Where the elytral ground colour is black there are red or orange subhumeral marks (cf. Coccinella heiroglyphica and Chilochorus spp.) and the margins are not explanate (Exochomus). These dark specimens are variously marked orange but if only one mark is present it is always subhumeral and touching the side margin.

Description from 10 Watford specimens at X10