Phaedon concinnus Stephens, 1831
This very local and generally rare species occurs around the coast and estuaries of England, Wales and western Scotland, the usual habitats are salt flats, saltmarshes and tidal river banks where adults occur on a range of herbaceous plants but mostly Sea Plantain (Plantago maritima L.) and Sea Arrow grass (Triglochin maritima L.) In Europe it is restricted to northern and western regions from France to Finland although it is absent from many Baltic countries and seems to be very local and rare throughout the range, further north it occurs in Iceland and across northern Russia to Kamchatka and the Chukchi peninsula, and in Mongolia it is reported to occur up to about 1500m. Adults are present year-round; they overwinter in the soil or among leaf-litter or moss in marginal situations and become active in March and persist into September or October, breeding occurs in the spring and oviposition begins in May. Females chew small cavities into the stems of host plants; Sea Arrow grass has been recorded hosting larvae, there are probably other species but in rearing experiments they would not feed on plantains, and larvae emerge after about ten days. They feed openly on foliage and develop rapidly, passing through three instars and being fully-developed by late July or August, at which time they enter the soil and pupate within a cell formed from the substrate. New-generation adults have been recorded in late July and early August, they feed mostly on Sea Arrow grass and Sea Plantain but have also been recorded eating leaves and flowers from buttercups (Ranunculus L.) and , abroad, on Cochlearia arctica Schltdl. Ex DC. foliage. They are fully-winged and disperse by flight, both larvae and adults may be observed on host foliage but adults may spend much of their time low down on stems and leaves near the soil and so may need to be looked for carefully.
3.0-4.1mm. Elongate and broadly-oval, entirely bright metallic green or greenish blue, sometimes with a coppery reflection or, rarely, entirely metallic blue, and bicoloured specimens occur where the forebody and scutellum are dark blue and the elytra metallic green or coppery. Distinguished among our UK species of Phaedon Latreille, 1829 by the form of the pronotum; the disc has a mixture of fine and coarse punctures and the lateral margins have a distinct isodiametric microsculpture. The rare entirely metallic-blue form might be mistaken for P. cochleariae but here the underside of the basal antennomeres is pale, at least to some extent, while in the present species the antennae are entirely black. The elytra have distinct punctured striae and randomly and more finely interstices but they lack the humeral calli seen in P. armoraciae. Among our other chrysomelid fauna they are distinguished by the colour and form, striate elytra which lack the apical ‘comb’ seen in Chrysolina, tibiae which are smooth externally and lack apical spurs and the form of the antennae; the insertions are widely separated and the last four segments form a narrow, loose and elongate club.