Many species are brownish or blackish, but some species are brightly colored. The long, curved mouth parts form a beak which is carried beneath the body, with the tip fitting in a groove on the underside of the body. The middle of the abdomen is often widened, so the wings don't completely cover the width of the body. The female lays eggs in tight, upright clusters on leaves or in the soil. Nymphs resemble miniature, wingless adults.
Most assassin bugs are generalist predators in gardens and fields.
They sit in wait of prey and are most likely to attack small flying insects, however they can subdue and kill medium-sized caterpillars and similar insects. Some prey in vegetable plantings include aphids, leafhoppers and asparagus beetle eggs and larvae. They may feed on beneficial species as well as pests. Although they have not been specifically manipulated for biological control, they do contribute to natural control and their conservation by judicious pesticide use is beneficial. The wheel bug, Arilus cristatus , is one of the largest and most easily recognized assassin bugs.