Many shield bugs or stink bugs (pentatomids) are predatory and can attack beetles and caterpillars. These bugs have glands in their thorax between the first and second pair of legs which produce a foul smelling liquid. This liquid is used defensively to deter potential predators and is sometimes released when the bugs are handled carelessly. They are called shield bugs because their bodies are usually shaped like shields.
Isaacs, Rufus. True bugs. Michigan State University Cooperative Extension Service. 2009. Retrieved 01 July 2010.