Sphaeriusidae
Sphaerius acaroides Watlt, 1938 is the only member of the suborder Myxophaga to occur in the UK. It is a tiny beetle; only some 0.7mm in length, short oval and very convex in form, entirely black or dark brown, glabrous and shiny. The species exhibits a combination of features unique to our fauna; the antennae are 11 segmented with an elongate 3 segmented club, there are distinct notopleural sutures on the prosternum, only three abdominal sternites are visible and the hind coxae are expanded into very large femoral plates. The legs are short with broad and flat tibiae, especially the front pair. See our guide for a discussion on this species.

There are very few modern records of this species; west Dorset and Cambridge are given on the NBN while Crowson writing in 1954 states that he was unable to find records from the previous thirty years. Adults occur under debris on areas of wet alkaline peat in central and eastern England (Crowson). Hurka describes a similar habitat; under plant debris and algae on sandy soil at the water's edge or among or on peaty soil. The broad and flat larvae, which lack urogomphi, probably feed on algae.

Although we have not recorded the species locally we feature it because it is such an interesting beetle. Searching for it would, obviously, require some dedication but it seems reasonable to suppose that the species may have been overlooked and to find it would, equally obviously, justify the effort.
A splendid photograph of a set specimen is given in Hurka.

Following the publication of this page (spring 2009) we received some helpful advice from Andrew Duff which, with his permission, we are very happy to include.

'This species is well established at temporary pools on soft rock cliffs at Eype Mouth in Dorset, where I discovered it in 1990 (EMM 128: 214, 1992). I know it's been recorded several times subsequently and as far as I know it's still there. Sphaerius could well be in your area but it's hard to spot. You have to peer closely at the mud looking for tiny black mite-like beetles (hence the name 'acaroides') walking slowly along. Try at plant roots at the edges of very shallow ponds where the mud is soft and damp, especially on hot days in mid summer.

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