Phyllopertha horticola (Linnaeus, 1758)
Widely distributed throughout Britain and formerly very common everywhere being long regarded as a pest species in many situations but now much less common. As with many chafers there are years of great abundance sometimes with many years intervening, it is still occasionally found in large numbers in Cumbria (Jessop). The species lives on grassland, often on poor or calcareous soil, where the larvae feed on a variety of roots and sometimes in large numbers; Raw (1951) records up to a million per hectare. They may thus cause serious damage to grazing pasture and gardens, infested turf drying out and becoming hollow beneath. Birds are significant predators, often tearing up turf to find them. Adults emerge from April to June usually leaving the pupae in a mass emergence during mid morning and then swarming in bright sunshine. They feed on a variety of trees and shrubs and may cause damage to fruit trees and nursery stock. We have only very occasionally found the species in the Watford area, during hot weather they may be found on flowers, in our experience Crataegus seems to be attractive to them. Interestingly the species has been found in large numbers in the stomachs of Brown Trout in Welsh rivers (Seymour-Jones, 1953).

A striking and very distinctive species although without experience Hoplia might be mistaken for this in the field.

7-12mm. Antennae black or with basal segment brown, club with three lamellae in both sexes. Head and pronotum bright metallic green with long outstanding pubescence. Head much more densely punctured than pronotum. Pronotum bordered throughout, front angles protruding and enclosing a small depression. Hind margin strongly sinuate. Scutellum metallic and punctured as pronotum. Elytra light or dark chestnut brown, darker laterally and along suture and with long, erect dark pubescence throughout. With prominent raised shoulders and regular strongly punctate striae although the puncturation tends to be confused basally. Last two abdomnal segments exposed although strongly deflexed so not usually visible from above. Legs and underside black. Meso and meta tibiae with long white pubescence on inner face. Claws strongly incurved, front and middle claws unequal; outer claw much longer and split longitudinally from tip. Hind tarsi with two claws (cf. Hoplia) almost equal, the outer a little longer but not split. Pro tarsi thicker in male.

Description from 2 Watford specimens at X10

Raw, F. 1951. Ecology of the garden chafer, Phyllopertha horticola, with preliminary observations of control measures. Bull.Amat.Research 42:605-646.
Seymour-Jones, B. 1953. The diet of Trout in some Welsh lakes. Fishing Gazette 135:988-9, 1005-6.