Anthidium (Anthidium) palmarum are black with light reddish-brown to dark brown antennal flagellum and yellow maculations (Gonzalez and Griswold 2013). Females have white pubescence, except for ferruginous hairs found on the vertex, pronotal lobe, scutum, axilla, scutellum, inner tarsi, and center of S6. Females range in body length from 7.2–9.4 mm (Gonzalez and Griswold 2013). Male terga have finer punctures and broader impunctate apical margins than those in females. Males range in body length from 8.8–13.1 mm (Gonzalez and Griswold 2013).
(modified from Gonzalez and Griswold 2013)
Female A. palmarum can be distinguished from all North American Anthidium, aside from A. schwarzi, by the combination of the rounded sublateral lobes of T6 and dense tomentum on the basitarsi (Gonzalez and Griswold 2013). Female A. palmarum can be differentiated from A. schwarzi by the lack of a distinct lateral spine on T6, and the prominent yellow markings on the clypeus, paraocular areas, and mandibles (Gonzalez and Griswold 2013). Male A. palmarum can be differentiated from A. schwarzi by the narrow lateral lobe on T7, and S6 with a low lateral lobe and a shorter median lobe that is weakly emarginated.
Anthidium palmarum adults have been recorded in flight from February to early July, with peak activity occurring from April to May (Gonzalez and Griswold 2013).
Anthidium palmarum is a generalist that has been observed visiting a variety of species within Alliaceae, Asteraceae, Boraginaceae, Brassicaceae, Lamiaceae, Malvaceae, Onagraceae, Polygonaceae, Plantaginaceae, and Solanaceae (Gonzalez and Griswold 2013).
Anthidium palmarum nests are constructed in burrows in dead flower stems of Hesperoyucca whipplei (Agavaceae) (Hurd 1979). Males actively patrol the areas around the female’s preferred host plants, and will participate in confrontations when needed. Confrontations occur when the male needs to defend their territory from other territorial males, when they need to protect their territory from other insects, and when they participate in sexual encounters with females (Wainwright 1978).
Anthidium palmarum occur in the U.S. throughout southern California, Arizona, New Mexico, western Texas, southern Nevada, and southern Utah. In Mexico, they can be found in Baja California and Sonora. They are predominantly found in the Mojave, Sonoran, Baja California, and Chihuahuan Deserts. However, they also range north into southern San Joaquin Valley, southern Great Basin, Arizona mountain forests, and Colorado Plateau shrublands (Gonzalez and Griswold 2013).