Galerucella calmariensis (Linnaeus, 1767)
A locally common and sometimes abundant species occuring throughout England and Wales, including the Isles of Wight and Anglesey, north to the Mersey and north Yorkshire; in the west many records are coastal. Further north there are records from Cumbria and Man (NBN). The species is monophagus with both adults and larvae feeding on Purple Loosestrife (Lythrum salicaria), more especially where this is growing in wetland situations; the banks of rivers and ponds, marshes, fens and lakesides etc. Locally we have recorded adults on Common moor; along the Gade margins and on the western (wet) part of the moor generally. Overwintered adults appear on the emergent hostplants during April and commence feeding on the developing leaf buds, later in the season they produce small holes in the open leaves. Oviposition occurs mostly during May and June but extends into July, new generation adults appear from June and these begin egg laying after about a week so that oviposition periods of the two generations overlap. Overwintered adults perish in late summer. Adults emerging late in the summer do not lay eggs and only mature after hibernation. Eggs are laid in small batches underneath the leaves and hatch within two weeks. There are three larval instars, young larvae feed on developing leaf and flower buds while later instars feed on the lower leaf surface; badly infested host plants can be completely stripped of leaves. Pupation occurs in a cell a few cm below the soil surface and this stage is rapid with adults emrging within two weeks. Overwintering adults have been found in dead Reedmace (Typha) stems (Cox).

Sweeping mixed vegetation in likely situations will often produce several species; the dark pronotal mark is a good guide to which specimens to retain for examination. Adults will drop from a host plant at the slightest disturbance and so when trying to examine them it is as well to hold a net or beating tray beneath the plant.

3.6-5.6mm. Upper surface testaceous or brown, marked darker as described below, and very finely pubescent. Head distincly narrower than pronotum (our average is 9:13, see Pyrrhalta), base (generally from behind eyes) black. Coarsely rugose and indistinctly punctured, eyes convex and protruding. Antennae dark or lighter towards base, inserted in line with front of eyes, segment 1 longer than 2 or 3 or distance between insertions. Pronotum strongly transverse, sides curved to rounded from and hind margins. Surface strongly and widely depressed either side of middle, clearly punctured and rugose but for a narrow anterior border which is shiny and (almost) impunctate. All margins finely bordered. Usually with a median broad longitudinal black mark which is widened anteriorly but does not (in our specimens) reach the front margin. Scutellum black, elongate, surface rugose and unpunctured. Elytra relatively short; average ratio of pronotal:elytral length in our specimens 13:63, with explanate margin broad from behind shoulder to apex, not visible from above towards base. Epipleurs broad throughout. Testaceous, usually with a lateral longitudinal black from shoulder to before apex; usually widened apically. Puncturation random and large, much larger than the distance between punctures, cuticles between these very finely punctured and pubescent (X40). Legs testaceous, robust and relatively long. Third segment of all tarsi strongly bilobed; broader than basal segments. Claws small and appendiculate. Aedeagus distinctive; widest at base and truncate apically, in side view more strongly curved than in other Galerucella species

Description from 2 Watford specimens at X20