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The adult assassin bug is relatively large, usually 11 to 37 mm (0.5 to 1.5 in) in length. As with most true bugs, it has thickened forewings with membranous tips for handling prey. When at rest, the extended, segmented beak can be folded back underneath its body. Its folded wings overlap, giving the back a characteristic shape. Adults are commonly black, reddish, or brown, with long, slender legs, a narrow head, and round, beady eyes. Some species have sharp barbs on their forelegs to prevent prey from escaping.
All assassin bug species are predatory, primarily feeding on caterpillars and other insects. The assassin bug uses its needlelike beak to impale prey. It then injects a venom that both paralyzes and partially digests the prey. The body contents of the victim liquefy and are sucked out with the assassin bug's strawlike mouth parts. A few species, like the western bloodsucking conenose, commonly bite humans and other mammals. These bloodsucking species are sometimes called kissing bugs because they are attracted to exposed tender flesh, such as the face and lips of sleeping humans. Even species that prey only on insects can inflict painful bites on humans with inflammations that can persist for several days.
Eggs are laid openly in clusters on plants. The eggs of some species have spines or elaborately sculptured surfaces. They hatch into a partially developed larval form called a nymph. Nymphs are similar in form to adults of the same species, except that they are wingless, smaller, and often different in color.
One of the most common species is the leafhopper assassin bug. Adults are 1.5 cm (0.6 in) long and brown and reddish colored. A distinctive subgroup of assassin bugs are the threadlegged bugs, which have an elongated thorax (middle segment) and a slender body and legs. They are often brownish and resemble walkingstick insects.
Scientific classification: Assassin bugs are members of the family Reduviidae in the true bug order Hemiptera. Threadlegged bugs are members of the subfamily Emesinae. The leafhopper assassin bug is classified as Zelus renardii, and the western bloodsucking conenose as Triatoma protracta.