Timarcha tenebricosa (Fabricius, 1775)
This is generally the largest of our UK leaf beetles and the common name refers to the adult defensive behaviour of producing bright red haemolymph when alarmed or handled roughly, they do this by rupturing thin membranes in the mouth and forcing the liquid out in large drops, it is harmless although messy to humans but pungent and foul-tasting to predators. The beetle is a widespread western Palaearctic species though with a patchy distribution; it is locally common from Portugal and northern Spain to south-eastern Europe including Turkey and extends north to the Netherlands, UK and Iceland but is apparently absent from Poland and Fennoscandia, further east it extends into Russia and it is known from Japan. In the UK it is locally common across southern England and Wales including the Isle of Wight and Anglesey and there are a few scattered records extending north to Edinburgh. They may be found in a variety of open habitats, especially calcareous grassland and locally they occur on vegetation along canal towpaths, but also all types of grassland, meadow and agricultural borders, coastal sandy areas and dune slacks, heaths and wetland borders, upland acid moorland, bogs and tarns and along railway embankments. In the UK it is generally a lowland species but on the continent (Bulgaria) has been recorded up to 2400m. Adults are long-lived, up to 15 months, and may be observed year-round, they overwinter in the soil or among tussocks and moss etc. and may become active during mild spells, they generally emerge during April, soon become common and remain so into the autumn. Hosts include Cruciata laevipes Opiz (smooth bedstraw), Rubia tinctorum L. (common madder)and various species of Asperula L. (woodruff) and Galium L. (Bedstraws) including G. aparine L. (Cleavers), G. mollugo L. (Hedge Bedstraw), G. odoratum (L.) (Sweet scented Bedstraw), G. saxatile L. (Heath Bedstraw), G. uliginosum L. (Fen Bedstraw) and G. verum L. (Lady’s Bedstraw). Adults feed on foliage and stems, often conspicuously so and sometimes in numbers, early in the year low down among the stems and later, as the plants develop, they may be observed eating the stems from the terminal shoots downwards, they are flightless and during the warmest summer spells often take to walking across bare areas of soil. Mating occurs in late spring and summer and continues into the autumn. Oviposition begins in
Timarcha tenebricosa 1
Timarcha tenebricosa 2
Timarcha tenebricosa 3
Timarcha tenebricosa larva
the spring and continues into late summer; and after overwintering the same generation may continue to oviposit the following spring, the earlier eggs will produce a summer generation of adults from July until September while later ones will diapause and overwinter to produce spring larvae and a spring generation of adults. Eggs are laid among the host foliage either singly or in small batches and the female will cover them with plant debris and secretions or regurgitated leaves, each female may produce more than 200 eggs over a long spring and summer period so that with two overlapping generations all life stages may be present over long periods. Larvae emerge within 2 or 3 weeks and develop rapidly as they consume the host foliage, they pass through 3 instars and are fully grown within 5 to 8 weeks at which time they descend the stems and enter the ground to pupate. Pupation occurs from June in a shallow cell constructed from soil and secretions and adults emerge after 3 or 4 weeks. All life stages are distinctive, eggs are large, about 3.5mm, and tawny coloured while the larvae are fat and bloated-looking with deep folds between the abdominal segments, they are black with a metallic dark blue reflection, the head and thorax are more shiny and colourful than the contrastingly dull abdomen. The pupa is large and orange coloured and has a long apically bilobed process. Finding adults simply requires visually searching suitable host plants although their presence may also be detected by crushed specimens as they wander across pathways and towpaths in the summer.
The adults are large, 11-18mm , glabrous and entirely black or with a blue lustre and might only be confused with larger specimens of T. goettingensis (Linnaeus, 1758) but here the pronotum is evenly rounded laterally; in the present species it is strongly broadened anteriorly. The upper surface is dull due to rather strong isodiametric microsculpture which is obvious at X20. Without experience various species of Chrysolina may mistaken for bloody-nosed beetles but here the elytral epipleura are reflexed ventrally and delimited by a sharply-defined border, in Timarcha it is near-vertical and delimited by an ill-defined and often widely convex border.