Young, larval Giant Mesquite Bugs from the species neocalifornicus differ greatly in their appearance compared to the more mature form. This species is found mostly in the U.S.. They are usually found in large groups, clustered on a mesquite. They feed on the juices pulled out of its softer plant parts like new leaves, seed pods and young stems. Their coloration is quite bold. They are bright red with many vivid white horizontal lines along their backs. Along the 'spine' is a series of white dots with a few black rings in between them. Their legs have red and black bands. Females have flattened discs near the tips of their antennae. They emit a chemical that smells and is meant to deter predators from eating them.
Adults look darker, longer and have a triangular block of yellowish white lines crossing over their elytra. They may look dark brown or olive green with bright red bands on their black legs. Their sides are also red. They, too, can emit a chemical deterrent that has a noxious odor, but the make-up of it changes once they mature. It is thought that the chemical secretion morphs in order to be more beneficial against the different predators the bug encounters at particular life stages.