Scarabaeus (Scarabaeus) ritchiei ( MacLeay, 1821 )

Harrison, J. Du G., Scholtz, C. H. & Chown, S. L., 2003, A revision of the endemic south-western African dung beetle subgenus Scarabaeus (Pachysoma) MacLeay, including notes on other flightless Scarabaeini (Scarabaeidae: Scarabaeinae), Journal of Natural History 37 (3), pp. 305-355 : 347-348

Scarabaeus (Scarabaeus) ritchiei ( MacLeay, 1821)

( figures 16 , 33 , 51, 72)

Mnematium ritchiei MacLeay, 1821: 506 ; Reiche 1841: 212; Reiche 1842: 93; Reitter 1894: 183; Ferreira, 1961: 26; Balthasar, 1963: 138.

Scarabaeus (Mnematium) ritchiei (MacLeay) : Bedel 1892: 282.

Mnematium ritchiei ritchiei MacLeay : Gridelli, 1930: 324; Zunino, 1984: 96.

Mnematium ritchiei bottoi Gridelli, 1930: 324 ; Zunino, 1984: 96.

Pachysoma ritchiei (MacLeay) : Holm and Scholtz, 1979: 226.

Scarabaeus (Scarabaeus) ritchiei (MacLeay) : Mostert and Holm, 1982: 275.

Diagnosis. Clypeus quadridentate, clypeal teeth pointed and separated by ‘U’- shaped depression; posterior edge of genae without pointed flange, genae unserrated, but produced into an extra tooth on anterior edge ( figure 33 ); protibia quadridentate, serrations between and proximal to teeth, spurs simple ( figure 51); sub-elytral ridge and rim small, elytral striae vary from faint to distinct between specimens, humeral calli absent; metatarsal claws shorter than last tarsal segment (LTS), and approximately equal to width of LTS; male genitalia simple ( figure 72a, b).

Distribution and habitat. Coastal vegetated sand dunes ( Balthasar, 1963) in Libya ( figure 16 ).

Comments on locality data. The type locality for Mnematium ritchiei , i.e. Mourzouk (Murzuq or Marzuq) when compared to most of the coastal locality records, is far inland ( figure 16 ). The distribution maps of Balthasar (1963) and Mostert and Holm (1982) do not show this clearly. The town Murzuq is close to the ‘Sahara Murzuq’, which are presumably inland sand dunes.

There are no locality records joining the two subspecific populations of S. (Scarabaeus) ritchiei , but one would expect their distributions to have been continuous at some previous time along the coastline.

Morphological variation. Gridelli (1930) described the subspecies Mnematium ritchiei bottoi , which has a Cyrenacian distribution ( figure 16 ). Schatzmayr (1937) synonymized it with M. ritchiei . Zunino (1984), using male genitalia and differential reduction of the hind wings, recognized the two subspecies as valid. Because only specimens from Tripoli (31 ° 00 ∞ N, 15 ° 00 ∞ E) were examined, no comment can be made on the validity of S. (Scarabaeus) ritchiei bottoi . However, from experience with coastal S. ( Pachysoma ) species one would expect a degree of clinal variation across the geographic range of flightless S. (Scarabaeus) ritchiei .

Biology. Biology unknown. Various authors have assumed that S. (Scarabaeus) ritchiei roll balls like flying Scarabaeus (e.g. Balthasar, 1963). The mouthpart morphology appears intermediate between that of wet dung feeding S. ( Scarabaeus ) and dry dung feeding S. ( Pachysoma ), which suggests a mixed diet of both wet and dry food.

Comments. The size of the mesosternal ridge and hind wing buds (see Zunino, 1984) suggests that S. (Scarabaeus) ritchiei have not been flightless for as long as S. ( Pachysoma ) species. There is no marked setal development, a typical adaptation for dealing with soft dune sand.

Types. Mnematium ritchiei was described from a single specimen that is now in the BMNH collection (‘The only specimen known of this interesting insect is now in the British Museum...’. MacLeay, 1821). MacLeay (1821) includes the following data about the specimen, ‘Mourzouk, October 1819, D.Ritchie’, but this is not on the label itself.

Type material examined ( 1 3). LECTOTYPE 3, Mnematium ritchiei, MacLeay : Vigor’s Type (‘Vigor’s’ written, ‘Type’ typed, on white disk surrounded by a red circle) / Ritchii ML / (written, on now faded white paper) / Babary. (not traced), Capt. Lyon. (typed) / 59.57, Vigors Coll. (typed), (1 3 BMNH).

Additional material examined from Libya (S26uns. specs, 2 3 diss.).

Figures

FIGS 14–17. Distribution of flightless Scarabaeus (Scarabaeolus) and Scarabaeus (Scarabaeus) species in Africa, the Middle East and Madagascar. (14) S. (Scarabaeolus) scholtzi in Somalia. (15) S. (Scarabaeolus) silenus in Sinai, Syria, and Iraq. (16) S. (Scarabaeus) ritchiei in Libya. (17) S. (Scarabaeus) sevoistra in Madagascar. See figure 2 for distribution of S. (Scarabaeus) cancer in Angola.

FIGS 18–35. (18–30) Head of Scarabaeus (Pachysoma) species in dorsal view: (18) S. (P.) aesculapius. (19) S. (P.) hippocrates. (20) S. (P.) glentoni. (21) S. (P.) endroedyi. (22) S. (P.) striatus. (23) S. (P.) gapiepinus. (24) S. (P.) bennigseni. (25) S. (P.) schinzi: (a) female, (b) male. (26) S. (P.) valeflorae: (a) female, (b) male. (27) S. (P.) fitzsimonsi. (28) S. (P.) rotundigenus. (29) S. (P.) rodriguesi. (30) S. (P.) denticollis. (31, 32) Head of flightless Scarabaeus (Scarabaeolus) species in dorsal view. (31) S. (Scarabaeolus) scholtzi. (32) S. (Scarabaeolus) silenus. (33–35) Head of flightless Scarabaeus (Scarabaeus) species in dorsal view. (33) S. (Scarabaeus) ritchiei. (34) S. (Scarabaeus) sevoistra. (35) S. (Scarabaeus) cancer.