The superfamily Scarabaeoidea contains four families that occur in Britain and Ireland:
Geotrupidae (7 species): the dor-beetles (Anoplotrupes, Geotrupes and Trypocopris) and the Minotaur Beetle Typhaeus typhoeus, all of which are primarily dung-feeders. Plus Odonteus armiger which feeds on fungi.
Trogidae (3 species) in genus Trox. Mainly associated with dry carrion, not with dung.
Lucanidae (4 species): the Stag Beetle Lucanus cervus, the Lesser Stag Dorcus parallelepipedus, the Rhinoceros Beetle Sinodendron cylindricum and the long-extinct Platycerus caraboides. The three extant species are all saproxylic, breeding in large girth timbers in a fairly late stage of decay.
Scarabaeidae (83 species) is the largest family and contains mostly dung-feeders but also a few which feed on decaying vegetation (before it has been digested by a mammal), a few saproxylic species, and the 16 species of chafer, none of which are dung-feeders.
The Scarabaeoidea are often referred to as the “dung beetles and chafers” or even just the “dung beetles”. It’s a useful shorthand but it doesn’t do justice to the varied ecological roles of species in the superfamily.
The main identification guide is Les Jessop’s RES Handbook (Jessop, 1986). It is out of print so can be downloaded free from here. Jessop’s Handbook also includes larval keys to genus. The 1986 Handbook superseded an earlier RES Handbook by E.B. Britton (1956) which I have to confess I have never used though Darren Mann has told me often enough that it is better in places than Jessop: download it here.
The most troublesome genus of scarabs, and by far the largest (42 species), is Aphodius. I’ve put this webpage up mainly to make Martin Harvey’s excellent new document available, which makes identifying Aphodius with Jessop’s keys much easier. Download the PDF here (version 1, 10th February 2015). The document provides an excellent set of photos from Darren Mann, with accompanying text, for use alongside Jessop’s keys.
Darren Mann is the British expert on Scarabaeoidea, runs the national recording scheme, and has encouraged lots of people to poke about in poo looking for beetles.
John Walters has produced an excellent photographic ID guide to the Geotrupidae (best to right-click on the link and choose to save the PDF to your computer). It’s the best publication there is for identifying these species and is now freely available for download.
For an excellent set of photos and genitalia illustrations of central European Scarabaeoidea, the small book by Marek Bunalski (1999) is a good buy, even more so if you can read German but worth having for the photos and illustrations alone.
Britton, E.B. (1956). Coleoptera. Scarabaeoidea (Lucanidae, Trogidae, Geotrupidae, Scarabaeidae). Handbooks for the Identification of British Insects, vol. 5, part 11. London: Royal Entomological Society.
Bunalski, M. (1999). Die Blatthornkäfer Mitteleuropas. Coleoptera, Scarabaeoidea. Bestimmung – Verbreitung – Ökologie. Bratislava: František Slamka.
Jessop, L. (1986). Dung beetles and chafers. Coleoptera: Scarabaeoidea. Handbooks for the Identification of British Insects, vol. 5, part 11. London: Royal Entomological Society.