Red-shouldered Leaf Beetle
Saxinis sonorensis (?)
This beetle was photographed while on leaves of Foothills Palo Verde, at White Tank Mountains, Maricopa Co., Arizona on 12 Aug. 2017. Length about 4 mm.
Chrysomelidae -- Leaf Beetle Family
Red Shouldered Leaf Beetles belong to the group of leaf beetles known as casebearers which get their name from the immature grub stage which builds a hardened case made from fecal material. The soft-bodied grub is protected inside from desiccation and is camouflaged from predators by appearing as something quite inedible. Predacious ants also seem repelled by the case material. Each species of casebearer tends to specialize on one or a few plant species. However, because the larval stage is obscure and hard to find entomologists may have difficulty in definitively linking beetle and host plant.
There are many species of casebearer leaf beetles found in the Sonoran Desert and several belong to the genus Saxinus. From above the head is nearly concealed by the pronotum.