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A large family (362 species on the 2012 edition of the British list) which includes some of the largest and showiest British beetles, reaching 30mm long. With such a large group – there are more carabids on the British list than there are breeding bird species - carabids can be found almost anywhere, but riparian and coastal habitats seem particularly species-rich.
Traditionally sub-divided into many subfamilies, the 2012 British list recognises only four: Cincindelidae (five species of tiger beetle), Brachininae (two species of bombardier beetles), Omophroninae (one species), and Carabinae (the ‘traditional’ ground beetles, 354 species).
The one British species of Omophroninae is Omophron limbatum (Fabricius), a semi-aquatic species found burrowing in sand around flooded sand-pits. Rather more rounded than most carabids, the species is a straw-yellow colour with darker patterning, reminiscent of a 14-spot ladybird (Propylea quattuordecimpunctata (L.)).
The two species of Brachininae, the bombardier beetle Brachinus crepitans (L.) and the streaked bombardier beetle B. sclopeta Fabricius, both of which are famous for their ability to expel a 100°C jet of chemicals from the anus to deter predators. This is produced when hydroquinone and hydrogen peroxide from separate glands are mixed, and the resulting explosion can be heard as an audible crackle. Both species are 6-10mm long and have an orange head and thorax, and blue-green elytra, B. sclopeta with an orange streak down the elytral suture. Brachinus crepitans is found mainly on calcareous grasslands, arable field margins and chalk quarries, with most modern records from coastal areas, while B. sclopeta has always been rare and is now only found on a handful of brownfield sites in London.
The Cincindelidae were previously raised to family level, but have been regarded as a subfamily within Carabidae since 1974. The five British species are relatively large (8-19mm) and brightly-coloured. Diurnal predators, they can be found running at speed in open, dry situations primarily in spring and early summer. Larvae lurk at the bottom of vertical tunnels which act as pitfall traps for small invertebrates.
Carabinae is by far the largest subfamily, and includes both the largest and most frequently encountered species, such as Carabus violaceus L., Carabus problematicus Herbst, Nebria brevicollis (Fabricius), and Pterostichus madidus (Fabricius). Most are ground-dwelling predators or scavengers, but others burrow in the soil (tribes Broscinae and Scaritinae), forage on tree branches (various Dromiini), or in the intertidal zone (Aepus marinus (Strom) & Aepus robinii (Laboulbene)). Most are largely nocturnal, but several large-eyed species are diurnal (Elaphrus and Notiophilus spp. in particular)
Many species have pronounced habitat preferences, and coastal habitats, upland moorland, woodland and riparian shingle all have distinct faunas. Several come to light, particularly Ophonus spp.