Omophron limbatum (Fabricius, 1777)
ADEPHAGA Clairville, 1806 CARABIDAE Latreille, 1802
OMOPHRONINAE Bonelli, 1810
Omophron Latreille, 1802
This species, the only member of the subfamily to occur in the U.K, was first discovered at Rye Harbour, East Sussex, in 1969 and since that time appears to be spreading; there are records from several coastal localities in Kent and a few inland from Norfolk and Suffolk. On the continent it is very widely distributed; from Spain to western Asia and Siberia. Adults are strictly riparian, occurring among fine substrates on the margins of lakes, ponds and streams and also around coastal seepages and outpourings. They may be abundant where found. The adults occur between April and October and are nocturnal; hunting and flying by night and hiding among the substrate or under stones etc. during the day. They are very agile and can move fast, especially when digging in fine sand when they can vanish rapidly. Fully grown larvae occur in spring and summer and may take 2 years to develop.
Within the Carabidae Omophron cannot be mistaken for any other genus and with only a single U.K. species the identification is assured. 5-6.5mm. Pale yellow or brown with most of the head, the disc of the pronotum, and 3 transverse marks joined along the elytral suture dark and brilliant metallic green. All appendages pale. Head and pronotum with strong, and sometimes rather sparse, punctation. Head transverse, with large and convex eyes. Mandibles stout, produced forward and obvious from above. Pronotum immovably fixed to the mesothorax; the hind margin is produced and covers the scutellum, and the prosternum is enlarged, covering the mesosternum. Pronotal front angles produced. Each elytron with 15 punctured stria. Male with 2 pro-tarsal segments and 1 meso-tarsal segment dilated.
OMOPHRONINAE Bonelli, 1810
This subfamily contains the single genus Omophron Latreille, 1802 with about 70 species divided into 2 subgenera; Omophron s.str. with about 20 species, and Phrator Semenov, 1992 with the remainder. The genus is Holarctic, extending south to Central America, South Africa, Malaysia and The Philippines. About 17 species occur in the new world. Species of Phrator are mostly Palaearctic and African.
The species are all very characteristic and similar in appearance; oval and very convex, and with long legs adapted for running. The dorsal surface is generally some shade of brown or yellow with a pattern of darker, often metallic, markings although all-dark species also occur. The scutellum is always hidden beneath a backward extension of the basal margin of the pronotum. The elytra are generally striate but lack a scutellary stria. The antennae are relatively long and inserted in front of the eyes, outside the base of the mandibles. In most species the mandibles are well developed and produced forward, obvious from above. The wings are generally well developed and most species are good fliers.
Typical habitat is wet soil or sand near standing water. Adults are gregarious and nocturnal, hiding by day among the substrate or under stones etc. They are most easily found by searching under stones etc. or soaking the substrate and waiting for the adults to emerge from their flooded burrows. Both adults and larvae are predators but will also take seeds and may damage crop seedlings on damp soil. At night they are usually found running on the soil or sandy surface, or burrowing into it, and may occasionally be seen running on the water surface. Some species are attracted to light.