The mouthpart is a rostrum, a stout three-segmented beak folded back under the head and swung forward to strike. Inside it lie fine stylets that pierce the prey's cuticle. Saliva containing paralytic and proteolytic components is pumped in; muscle and organ tissue break down into a soup, and the bug sucks it out, leaving the emptied exoskeleton.
Wheel bugs take caterpillars, beetles, sawfly larvae and other insects, including pest species, and are correspondingly welcome in gardens. Nymphs hatch in spring from a cluster of bottle-shaped eggs, are red and black, and lack the crest, which appears only at the final moult.
The crest itself has no confirmed function. It is often assumed to deter predators or protect the thorax, but neither has been demonstrated. What is well documented is the bite, which is defensive rather than predatory and reported as more painful than a wasp sting.