(Thasus gigas)

The adult is two inches long. 
Feeds by sucking up plant juices and is extremely fussy about what plant it will use as food. It will accept all species of mesquite, but nothing else.
When handled, these insects produce a potent, smelling secretion, but are otherwise harmless. Eggs look like small brown pillows glued in rows along the stems of the mesquite. Nymphs hatch from eggs in the spring and then die by the end of summer, leaving new eggs to overwinter until the following spring.

Source: Insects of the southwest (Floyd Werner, Ph.D. & Carl Olson, M.S.)