Thanasimus Latreille, 1806 

Thanasimus formicarius (Linnaeus, 1758) 

Ant Beetle

The common name of Ant Beetle refers to their mimicry of Velvet Ants' (Hymenoptera, Mutillidae) aposematic colouration. Female velvet ants occupy similar habitats, are wingless and are noted for their extremely painful sting.  This is a very widely distributed European species occurring from France east and north to Scandinavia and Asia Minor. In the U.K. it occurs throughout southern England to the Humber and sporadically further north. In Wales only in the south and mostly towards the coast. From Scotland there are records from the Highlands but it seems to be absent from the south. Adult beetles are relatively soft bodied but with well-developed and strong mandibles for dismembering adult scolytids. Adults emerge from overwintering during the early spring and fly to the lower parts of trees to hunt insects, generally scolytid beetles. They respond both to scolytid pheromones and to volatiles produced by damaged areas of host trees and for this reason they are often found in scolytid pheromone traps. Thus Thanasimus actively seeks out and lands upon trees that have been attacked by, or contain, scolytids. A wide range of scolytid beetles are prey; 27 species among the following genera have been recorded: Dendroctonus, Dryocoetes, Hylastes, Hylesinus, Hylurgops, Hylurgus, Ips, Leperesinus, Orthotomicus, Pityogenes, Pityokeines, Polygraphus, Scolytus, Tomicus and Trypodendron. Consequently a range of both broad-leaved trees ; oak, ash, poplar, elm etc. as well as conifers; pine, spruce, larch, Douglas fir etc. hosting scolytids will attract Thanasimus. By far the most common host is pine and the most common prey are pine bark beetles, Tomicus piniperda and T. minor and, often, the European spruce bark beetle Ips typographus. After flying to suitable trees they may be seen waiting or patrolling for their prey on standing or fallen timber. Stacked logs or felled trunks are particularly attractive to them. Mating occurs from March onwards and continues into the summer. Males pursue females among bark crevices and hold them firmly with the mandibles around the pronotum  while mating. Eggs are laid from April to June in small batches of 20-30 in bark crevices, often close to scolytid borings. Larvae hatch after about a week and live under bark etc. where they consume bark beetle eggs, larvae and pupae as well as other insects. They are very agile and quick, being able to move freely along the scolytid tunnels and even move backwards. Growth is very slow and they may spend two years in the larval stage. Pupation occurs in the autumn under bark in a chamber lined with mucus and debris. Adults eclose the following spring. Adults are sometimes found under bark and often near the distinctive pink larvae. We have found them on several occasions under close fitting pine bark and on one occasion, at Bricket Wood Common, several were found under loose dry beech bark on a dead stump. Stacked logs and trunks are especially good habitats to search for the adults; during May and June 2015 they were common in Whippendel Wood on stacked pine and mixed deciduous logs. To see them active it is more or less essential to search nocturnally. Adults roam the logs looking for scolytids or mates, several pairs were found. When found the adults grab the prey quickly with all legs so that it cannot escape, then it bites between the thorax and abdomen or the head and thorax to extract the soft tissue. Scolytids are consumed within about 10 minutes and each ant beetle will consume on average 3 beetles daily. Adults live for between 4 and 10 months.

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Within the U.K. fauna T. formicarius can only be confused with our other species of the genus but they are easily separated on the colouration alone.

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6-10mm. Head, thorax and base of elytra with long erect fine setae. Head black, as wide as the pronotum. Vertex convex and rugosely punctured. Eyes prominent, transverse and curved in front of antennal insertions. Labrum deeply incised at centre. Mandibles robust and produced forward. Antennae pale at base becoming darker apically. Last 3 or 4 segments form a weak and loose club. Pronotum quadrate with a deep transverse impression around the apical third and a wide median impression behind this. Black anterior to the depression and red behind. Margin regularly curved from constriction to base. Surface densely and quite strongly punctured. Elytra parallel sided or weakly dilated towards apex. Anterior fifth red, remainder black with two transverse bands of dense white recumbent pubescence. With strongly punctured striae at base which may extend further back laterally. Legs entirely black but for the red tarsi.  The small first tarsal segment, when viewed from above, is hidden below the second. The third and fourth segments are very widely lobed beneath. Fifth segment gradually widened to the apex. Claws smooth. Underside dark with the abdominal sternites and prosternum red.

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Thanasimus femoralis (Zetterstedt, 1838) 

Our other species of the genus was added to the U.K. list in 1913. It is similarly widespread in Europe and the two are sometimes found together. In the UK it occurs only in the Caledonian pine forest remnants in N.E. Scotland although it has occasionally been recorded from plantations. It has similar habits and life history to formicarius. At 6-8mm. it is on average smaller than formicarius and with red legs and black prosternum it should be easy to separate the two.