Extracted from: Grigarick A.A., & Stange L.A., (1968). The Pollen Collecting Bees of the Anthidiini of California (Hymenoptera: Megachilidae) Bulletin of the California Insect Survey Volume 9.
Geographic range.—Southern California, Colorado Desert. California records.—RIVERSIDE Co.: Desert Hot Springs, 3 mi. NE, 1 6\ 1 9, XI-8-63 (R. McDiarmid, LACM).
The color of both sexes of this species is black with pale yellow maculations. The metasomal bands are closed to form a black spot more typical of other genera of the tribe.
H. autumnale exhibits a number of morphological characteristics similar to H. timberlakei and H. zebratum. The females of autumnale are distinguished with a clypeus with a relatively smooth apical margin and a tergum VI that is nearly straight when viewed from the side (fig. 122), contrasted to the toothed clypeus and convex tergum VI of timberlakei (fig. 126). Both sexes of autumnale have more strongly developed forecoxal projections and carinae on the leading edge of the pronotal lobes than timberlakei.
No information is known of the biology of this rare species. Its scarcity may be attributed to the infrequency of collections in the fall season.