Lomechusoides strumosus (Fabricius, 1792)
Lomechusoides is a small Palaearctic genus of 14 species, the present species is the most widespread in the west, and a further species, L. teres Eppelseim, 1884, occurs in parts of Fennoscandia and Eastern Europe, but the remainder occur in Central and Eastern parts of Asia. L. strumosus is widespread in Central and Northern Europe from Spain to Italy and Romania in the south and extending north to the UK and the Baltic countries where it reaches the Arctic Circle in Sweden, there are also a few scattered records further east, from Georgia, Kazakhstan and Tibet, and a further subspecies, ssp. siculus Fiori, 1914, which is sometimes considered to be a distinct species, is known from Sicily. It is generally very local and rare throughout this range and in many countries is known from only a few records which in many cases are mostly from the 20th century. In the UK it is known from only a very few sites in Southern and Central England. This apparent scarcity is probably realistic but the species might be more frequent as adults spend much of their time deep in ant nests and are usually only recorded when they disperse. The species is strictly myrmecophilous, it occurs mostly in dry and sunny situations, often on moors, dunes and grassland but also in open woodland or on woodland margins on light or sandy soils, where the host ants are nesting in abundance. Hosts include various species of Formica L., frequently F. sanguinea Lat., but also F. rufa L. and F. polyctena Förster. Adults produce various chemicals that alter the ants behaviour, thus worker ants will approach beetles that appear near to their nests and investigate them; they are initially aggressive but they soon begin to sample chemicals exuded from various glands on the beetles body and legs, and this causes them to become passive and ‘adopt’ the beetles, carrying them into the nest and down into the brood chambers where they are fed and tended the same as the developing ant larvae; with ants feeding by mouth-to –mouth transfer of fluids (trophallaxis.) Adults oviposit among detritus in the brood chamber and the resulting larvae also produce chemicals that cause the ants to protect and feed them. Both adult and larvae are reared by the ants but they also predate ant eggs and larvae, apparently tolerated by the ants as they do so. Pupation occurs among detritus in the brood chamber. New generation adults appear in the autumn, many will migrate to find other nests where they will be adopted and spend the winter but others will remain in the nest and migrate in the spring. Interactions between the ants and beetles are complex and involve many chemicals that alter the ants’ behaviour, thus parasitized colonies often include numbers of pseudogynes (worker-queen intermediates), these have the forebody distended like a queen but a normal head and abdomen, and probably arise by queen larvae being neglected in favour of the beetles and their larvae , or by beetle larvae predating so many ant larvae that queen larvae are converted into workers in order to maintain the colony. A very good insight into beetle-ant interactions can be found here. Because adults spend much of their time deep within ant nests they are rarely found by normal collecting methods, but they often occur under stones or debris near to nests in the spring and autumn when dispersal occurs, even so they rarely occur in numbers.
Lomechusoides strumosus 1
Lomechusoides strumosus 2
5.5-6.5 mm. Superficially similar to Lomechusa but otherwise very distinctive among our UK fauna and unlikely to be confused with any other species. Entirely dark brown or with paler elytra, dorsal surface finely punctured and pubescent, basal abdominal tergites and femoral apices with tufts of dense pale brown pubescence (trichomes). Head small, much narrower than the pronotum, vertex flat and clypeus concave between almost flat eyes and short temples, clypeus emarginate between weakly raised antennal tubercles. Antennae inserted anteriorly, 11-segmented; basal segment enlarged and produced internally at the apex, segment two diminutive, 3-10 quadrate or slightly elongate, and the terminal segment long and pointed. Pronotum widely transverse, broadest across rounded posterior angles and gently narrowed to widely-rounded anterior angles and an almost straight apical margin, basal margin widely produced backwards. Surface longitudinally depressed either side of the disc, lateral margins raised and dull due to fine microsculpture, disc smooth, with scattered fine punctures, basal margin more densely punctured. Elytra transverse, almost parallel-sided from rounded shoulders to perpendicular apical angles, basal margin only slightly sinuate, surface more-or-less evenly flattened and finely punctured and pubescent throughout. Abdomen long and broad; basal tergites with strong lateral borders and rows of stronger punctures inside the apical margins, distal tergites very finely punctured throughout, sub-apical tergite strongly emarginate. Legs long and robust, femora and tibiae finely pubescent throughout, tibiae with short and very fine apical spurs. Tarsi 4-5-5 with all segments simple in both sexes.