Rhyssemus sonatus Le Conte & Horn 1881

Rhyssemus sonatus LeConte

Rhyssemus sonatus LeConte, 1881:77.—Henshaw, 1882:232.—Horn, 1887:89.—Leng, 1920:251.—Schmidt, 1922:507.

MALE.—Length 3.6 mm, greatest width 1.7 mm. Elongate, widest at middle of elytra, nearly parallel sided. Color dark reddish brown; head except clypeus, pronotum except anterior border and antero-lateral angle piceous to black. Head tuberculate, tubercles fine, dense on vertex, becoming coarse and less dense across front; clypeus finely tuberculate, anterior margin distinctly emarginate between dentate angles, feebly, narrowly reflexed. Pronotum 1.0 mm long by 1.4 mm wide; closely, densely, finely tuberculate, 4 transverse ridges present with tubercles only slightly coarser than between, all ridges narrowly broken at midline (Figure 4); lateral and basal borders narrowly margined, with fringe of evenly spaced, flattened setae. Elytra 2.4 mm long, 1.7 mm wide, humerus sharply dentate; striae deeply impressed, punctured, punctures separated by 4 to 6 times their diameter; intervals flat except sutural interval raised with single median row of tubercles, other intervals with 2 rows of tubercles, outer row large, rounded, inner row of tubercles small, elongate (Figure 4). Metasternum strongly alutaceous, broadly carinate between coxae. Metasternal midline extending from apex to base of metasternum; surface smooth, shiny medially, becoming alutaceous and slightly tuberculate laterally. Abdominal sterna weakly alutaceous, with fluting along anterior margin of each sternum and a row of indistinct tubercles extending from lateral border nearly to midline. Pygidium scabrous, strongly alutaceous, 6 erect, apical setae present and several short, erect setae scattered over surface. Foretibia smooth, with 3 lateral teeth, the posterior tooth slightly behind the middle of tibia; spur long, robust, feebly sinuate, not curved downward. Middle and hind tibiae equal in length to femora, each apex fringed with long, unequal setae and 2 spurs, outer spur short, sinuate, less than half as long as inner spur, inner spur longer than first tarsal segment, feebly sinuate. Hind tarsus shorter than tibia, basal segment as long as segments 2–4 combined, segments 2–4 slightly decreasing in length successively, 5th segment twice as long as 4th. Genitalia with lateral lobe long, slender, abruptly bent downward before apex; internal sac with 3 large, median sclerites and a patch of small spicules laterally (Figure 21).

FEMALE.—Similar to male except the pygidium is wider and the penultimate abdominal sternum slightly longer at middle.

VARIATION.—Length 2.7 to 3.7 mm, width 1.2 to 1.7 mm. The dorsal color varies from reddish brown to black. Specimens from northern Colorado usually have the pronotal ridges smoother and more apparent than described above and usually do not have tubercles on the sutural interval. The pygidial hairs are easily broken and there may be from none to eight present. Specimens with eight hairs are extremely rare.

TYPE-LOCALITY.—“near Chicago.”

TYPE DEPOSITORY.—Not located.

Rhyssemus sonatus is a species of aphodiine dung beetle in the family Scarabaeidae. It is found in North America.