Stridulomus sulcicollis (Péringuey 1886) - Stridulating Toktokkie

Stridulomus sulcicollis (Stridulating Toktokkie) is one of the enormous tenebrionid beetles, it is usally 60 mm in length, but may be up to 80 mm.
This species is easily recognized by a very large longitudinal median depression at the base of the pronotum ('sulcicollis') and told from other large Molurina species by the lack of distinct carinae on the elytral disc and the outer margins of the elytra contrasting to the disc due to small tubercles and setae.

Koch erected the genus Stridolomus (based on Psammodes sulcicollis Peringuey) which "is strikingly characterized by the presence of a strongly developed pseudo pleural-femoral stridulatory organ". (The part of elytra called pseudopleura by Koch is actually epipleura and it is the edge of the elytra.)

Stridulation as a defense mechanism against enemies is widespread in beetles and occasionally occurs in Tenebrionidae. However, for example, in many longhorn beetles (Cerambycidae) pronotum and elytral base rub together and thereby produce a sound that can also be heard by humans, the situation is different in Tenebrionidae, where elytra and legs rub together, which is inaudible to us and is evident only from the morphology. Sound production using different stridulatory mechanisms has evolved independently in a number of Tenebrionidae. An elytro-femoral mechanism occurs in several genera of African Tentyriini such as Imatismus and others where a linear file on the metafemur (plectrum) rubs against the sharp edge of the elytral epipleuron (strigil) and the same mechanism has evolved independently in several genera of the southern African Adelostomini and the genus Stridulomus (Koch 1955), which possesses a stridulatory surface on the outer edge of the epipleuron and a ridge on the hind femora.

Original description in:
Péringuey, L. 1886. First contributions to the South African coleopterous Fauna. Transactions of the South African Philosophical Society 3.
https://sci-hub.ee/10.1080/21560382.1881.9526176
Translated from Latin:
Oblong, black, slightly opaque; head punctuated; prothorax flattened, sides granulated, apex with a deep furrow; elytra oblong-ovate, the costae are obsolete on the first third, the sides and posterior part tuberculate.

Length 46/50 mm., width 29/22 mm
The head is trapeziformn and finely punctured, the epistome is separated from the head by a deep transverse impression, the eyes are very much emarginated in front. The antennae are slightly setulose.
The prothorax is a little broader than long, the anterior angles are acute, the outer sides rounded anteriorly and deflexed posteriorly, and the basal margin strongly sinuated; there is a fringe of yellow hair on the apical margin, and a longitudinal impression in the centre of the disc which is almost plane and finely punctured; the sides are strongly granulated, and on the posterior part there is a very deep sulcus, above the basal margin, as broad as the scutellum. The scutellum is large, finely punctured, and pointed at the apex.
The elytra are much broader than the prothorax at the base, and increase in width, being twice as broad in the middle; they are three times as long, moderately convex above, nearly smooth on the upper part of the disc, the outer sides and posterior part are covered with elongated tubercules pointing backwards, very dense and sharper near the apex, where they are much smaller and where are interspersed some very short fulvous bristles. Each elytron has three raised, nearly obsolete, lines; the first from the suture is smooth in the anterior part, and is the most conspicuous of the three which disappear among the tubercles towards the declivity. The epipleurae are very narrow and smooth.
In the male, the metasternurn is slightly pilose, the first three anterior segments of the abdomen are covered in the centre with a thick velvety fulvous tomentum which invades also the two last segments. The legs are short, very strong and punctured, and have a ridge of short fulvous bristles on the internal carina; the tarsi have short yellow bristles.
The underside is convex and rugose.
From the Zambezi River and Damaraland.

This species is illustrated (fig. 1I, with epipleuron) in:
Gearner, O. M. et al. 2021. Discovery of New Genera Challenges the Subtribal Classification of Tok-Tok Beetles (Coleoptera: Tenebrionidae: Sepidiini) . Insect Systematics and Diversity 5(2). doi:10.1093/isd/ixab006
https://sci-hub.ee/10.1093/isd/ixab006

Distribution: Kalahari (Namibia, Botswana, South Africa).

iNat observation:
https://www.inaturalist.org/observations/72359827

Posted on February 12, 2024 01:38 PM by traianbertau