Trichodes Herbst, 1792
POLYPHAGA Emery, 1886
CLEROIDEA Latreille, 1802
CLERINAE Latreille, 1802
T. alvearius (Fabricius, 1792)
T. apiarius (Linnaeus, 1758)
This large and mostly Holarctic genus includes about 100 species, 13 occur in North America and about 50 in the Western Palaearctic region, with eastern Mediterranean areas and the Middle East being particularly diverse, 26 are recorded from Europe and many of these are either of a restricted southern or eastern distribution which extends into North Africa or are endemic to certain areas e.g. T. zaharae Chevrolat, 1861 from Spain, T. creticus Brodsky, 1982 from Crete or T. albanicus Winkler & Zirovnicky, 1980 from Albania. Beyond this about 10 species are known from tropical Africa. Only four species are known from Central Europe; T. favarius (Illiger, 1802) is a local and generally rare species in Austria, Slovakia and Moravia etc. although it is more common further south and is the most common species in Greece, T. ircutensis (Laxmann, 1770) is a mostly eastern Palaearctic species which extends west into eastern parts of Europe and has been recorded (rarely) from Switzerland, Czech Republic and Poland. T. alvaerius (Fabricius, 1792) is widespread across southern and central Europe reaching into northern France, Germany and Poland although it has declined during the twentieth century and most distribution data is based on older records. T. apiarius (Linnaeus, 1758) is the most widespread and common species, it occurs from the Mediterranean to the Baltic Sea as far north as Denmark although it is becoming less frequent in northern areas.
With the exception of a few species known to feed on or within orthopteran oöthecae, the majority of species are associated with various species of solitary or social bees. Adults are diurnal and frequent flowers where they feed on pollen and predate small insects etc, they are usually active and fly readily and strongly. Mating occurs on flowers and males usually seek out females. Egg-laying habits fall into three catagories; females may lay eggs on flowers frequented by their hymenopterous hosts, they may lay them near to orthopteran oöthecae or they may deposit them inside or near to the nests of their hosts. Larvae of some exhibit phoretic behaviour by attaching to the adult host to be transported back to the nest. Inside the nest the young larva must enter a cell while it is being filled by the host bees as it seems they cannot enter a cell once it has been sealed, the larva initially feeds on the honey but
soon begins to devour its host larva, once the cell is empty it will either bore into an adjacent cell and continue feeding, remain in the cell to pupate or burrow into the surrounding substrate and form a pupal cell. So far as is known all specie pass through five instars, the first three of which actively feed and develop, the fourth prepared the pupal cell and lines it with an oral secretion, and the fifth will place itself in the cell with its head towards an exit hole and then pupate. In North America species occur either in the spring/summer or the summer/autumn; autumn species develop over two years, young larvae overwinter and develop in the spring and summer, fourth instars overwinter again and pupate late in the summer to produce autumn adults. Spring species are univoltine, developing in the summer and passing the winter as fourth instars in the pupal cells, and pupating in the spring to produce adults early in the year.
Adults are readily recognized by their striking colouration; they are black to bright metallic blue or green with bright red or yellow markings to the elytra which are generally arranged as transverse fascia which may meet at the suture or may be joined laterally. The antennal structure is also distinctive; rather short with elongate basal segments, quadrate to transverse distal segments and the last three larger and forming a gradual but distinct club which is truncate in most species. 8-30mm (European species). The body and appendage are clothed with dense erect and dark setae, usually of several lengths and often longest on the pronotum and the base of the head. The head is hypognathous with large convex and finely-faceted eyes which are incised anteriorly, and short temples, the punctation varies but other than a variously-developed longitudinal impression the vertex is simply convex. Antennae inserted laterally in front of the eyes and both the maxillary and labial palps have the terminal segment expanded apically. Pronotum quadrate to elongate, often broadest in front of the middle and constricted before the base, lateral margins sinuate and not bordered, basal and anterior margins straight or nearly so, surface indistinctly sculptured, usually with various shallow transverse impressions, punctation very variable but always distinct. Elytra elongate, with broadly-rounded shoulders and usually dilated behind the middle, the apical margin is continuous but the suture may diverge before the apex, leaving a gap, punctation strong and dense, usually extensively random but often forming longitudinal rows, especially towards the base. Legs robust and long with the femora always widely visible from above. Tibiae only weakly thickened from the base, usually curved to some extent and often strongly so, especially the hind tibiae, and all with small terminal spurs. Tarsomeres 1-3 strongly bilobed, the third subequal to the second, the fourth small and inconspicuous and the fifth long and curved. Claws smooth and separate to the base. In many the males may be recognized by their enlarged hind femora.
The two British species are easily separated:
9-16mm. Pronotum coarsely punctate, the punctures mostly discrete but in places confluent. Elytral apex dark metallic blue.
10-17mm. Pronotum finely punctate. Elytral apex (sometimes narrowly) pale.
Trichodes alvearius (Fabricius, 1792)
Trichodes alvearius (the type species of the genus) is included in the UK checklist on the basis a few old records from southern England; it became extinct in the 1800’s and is now very rare in northern Europe so the likelihood of specimens accidentally occurring here is small. Adults are active in warm weather from May to August, typically inhabiting flowers on wooded margins and hedgerows or in parks and gardens where they feed on pollen and small insects etc. Larvae develop in the nests of solitary and social bees where they predate their host larvae.
Trichodes apiarius (Linnaeus, 1758)
This species was for a long time considered extinct in the UK; it was formerly an established but very rare and sporadic native known from Hampshire, Kent, Norfolk and Lancashire and was last recorded from the UK in Kent around 1830, but in August 2019 a specimen from Hertfordshire, photographed on umbel flowers by Martin Parr, was presented on Facebook, confirming its UK presence but presenting questions about its origin or whether the species has been resident over longer periods. Adults occur in open and dry situations such as agricultural margins, meadows and roadsides, they are active in hot sunshine from May to August and are usually seen on a variety of flowers where they feed on pollen and predate small insects etc. they generally occur in numbers and are very active, readily flying between flowers as they feed. Mating pairs have been observed early in the season and females oviposit in the nests of solitary bees (species of Osmia Panzer, 1806) including the very common and widespread O. bicornis (Linnaeus, 1758) and Megachile Latreille, 1802) or in honey bee hives. Larvae develop quickly, predating their host larvae and pupating among nest debris or larval cells, but little more is known of the life-cycle in the wild.