Damsel Bug (Nabis alternatus)
by Dr. Hector Carcamo
The Damsel Bug is probably one of the most common predators, and therefore beneficial insects, we find in all crops. It can be abundant in fields and is a generalist predator that will eat whatever it can find and subdue. Jennifer Otani, AAFC, did a laboratory study in petri-dishes that showed it eats lygus bug nymphs.
"Both adults and nymphs are fast, aggressive predators. They grasp their prey and pierce the body, injecting toxic saliva that paralyzes prey and digests body contents they then suck up," from page 120, Agriculture & Agri-Food Canada Field Guide
My student Arash Kheirodin used DNA gut content analysis to show that along with lady bird beetles it is one of the top predators that consumed cereal leaf beetle larvae in wheat fields of southern Alberta.
We should point out that the damsel bugs have a close resemblance to the green grass bug (rice leaf bug) and even more to the Stenodema, a mirid grass bug common in grasses, not so much in crops.
You can find more information on the Iowa State University Bug Guide website
North Carolina State University also has an excellent entomology guide. This link has an indentification guide for adult and nymph stages of the damsel bug.