Anthidium (Anthidium) maculosum are dark brown to black with yellow maculations (Gonzalez and Griswold 2013). Females have white pubescence except for brown hairs on the clypeus, supraclypeal area, frons, vertex, inner basitarsi, depressed marginal zones of T1–T4, T5–T6, and apex of S6. Females have a body length of 8.5–11.5 mm, and males range in body length from 9.2–13.1 mm (Gonzalez and Griswold 2013).
(modified from Gonzalez and Griswold 2013)
Anthidium maculosum may be distinguished from all other North American Anthidium, aside from A. chamelense, A. rodriguezi, and A. parkeri, by the combination of hind tibial carina and dull frons with coarse and sparse punctures. Anthidium maculosum can be differentiated from A. chamelense and A. rodriguezi by the presence of maculations on terga and smaller body size (Gonzalez and Griswold 2013). Female A. maculosum can be differentiated from A. parkeri by the presence of denser tomentum on the outer surface of the basitarsi, as well as T6 with a weakly depressed area above the preapical carina and distinct lateral projections. Male A. maculosum can be differentiated from A. parkeri by the digitiform lateral lobe on T7, shape of S6 and S8, and the lack of light maculations on the scape (Gonzalez and Griswold 2013).
Anthidium maculosum adults have been recorded in flight from mid-February to November, with peak activity occurring from June to September (Gonzalez and Griswold 2013).
Anthidium maculosum is a generalist that has been observed visiting a variety of species within Agavaceae, Asteraceae, Boraginaceae, Convolvulaceae, Ericaceae, Fabaceae, Iridaceae, Lamiaceae, Malvaceae, Orobanchaceae, Plantaginaceae, Polemoniaceae, Rosaceae, and Verbenaceae (Gonzalez and Griswold 2013).
Anthidium maculosum nesting behavior was described based on nest trap observations (Krombein 1967). Based on these observations, it is presumed that A. maculosum nests in preexisting cavities. Nest plugs were comprised of only trichomes, or a combination of trichomes, pebbles, small pieces of wood, masticated plant materials, or pellets of lizard dung. Males have been observed displaying territorial behaviors, such as guarding the host plants that are preferred by the females (Alcock et al. 1977).
Anthidium maculosum occur from Honduras to the western U.S. Within the U.S., they are found in Texas, Arizona, Utah, Colorado, and California to western Oregon. In the U.S., they are present in hot deserts; the Great Basin and Colorado plateau; Mediterranean California grassland, chaparral, and woodlands; pine-oak forests; and other forests. In Mexico, they are commonly found within pine-oak ecosystems (Gonzalez and Griswold 2013).