The Distribution, Habitat, Diet and Forensic Significance of the Scarab Frankenbergerius forcipatus (Harold, 1881) (Coleoptera: Scarabaeidae)

1. What they did

Forensic investigators use insects to help work out what happened to a body, but this depends on knowing which insects turn up on dead animals and when. Flies on carcasses are well recorded in Africa; beetles much less so. Nothing had been published about the biology of the dung beetle Frankenbergerius forcipatus.

The authors placed the carcasses of three small dogs, already dead and slightly bloated, on hill crests at two sites near Grahamstown in South Africa’s Eastern Cape (one dog near Jameson Dam, two together near Waainek). Three weeks later they sampled the beetles once. They identified the beetles under a microscope, examined their gut contents, and sequenced part of a gene (cytochrome oxidase I) from some specimens. They also searched three South African insect collections for more specimens of the genus.

2. What they found

• Numbers: 33 Frankenbergerius forcipatus: 11 males and 11 females at Jameson Dam, and 4 males and 7 females at Waainek. No mating pairs or nesting were seen.
• Where on the carcass: the beetles were in the decomposing stomach region and in the loosened soil beneath, and seemed linked to the stomach contents rather than the flesh.
• Other insects: many histerid, trogid and staphylinid beetles, and some silphid, clerid and dermestid beetles and a few muscid fly larvae, mostly in the soil under the carcasses. There were no blowfly maggots.
• Diet: under 5% of the gut contents stained for chitin, a marker of fungi, so very little fungus had been eaten. There were no mushrooms or moulds at the carcasses.
• DNA: 12 partial gene sequences were lodged in GenBank. They varied by only 0.19%.
• Museum collections: no specimens beyond those already published were found.
• Range: the new sites lie close to 100 km south-west of the previous most south-westerly record (Pirie Forest).
• Habitat: both sites were a mix of fynbos and grassland, not forest, the habitat previously suggested for the species.

3. What they concluded

• The species is not tied only to forests. All five known localities are moist, hilly or mountainous, so it may live in such habitats generally.
• This is the first confirmed collection of F. forcipatus from any potential food source, and only the fourth for any species in the genus.
• The beetles appeared to feed on the dog’s stomach contents rather than its flesh, suggesting a generalist feeder on decaying material that uses carrion when available. The earlier idea that it eats mushrooms is not supported for now.
• It belongs to the community of insects present during the wet stage of decay, and probably arrives only once tissue has decayed extensively, making it a late coloniser. This makes it useful to forensic entomologists estimating time since death in what are likely to be the mountainous parts of eastern South Africa.

6. Other technologies, skills or innovations

• Identification with a published key, a dissecting microscope and, where needed, dissection of the genitalia; confirmed by a specialist at the national insect collection.
• Gut contents stained with aniline blue to detect chitin from fungal cell walls.
• DNA extracted and a section of the cytochrome oxidase I gene sequenced, with sequences lodged in GenBank.