Despite the sinister name, most assassin bugs look pretty harmless. In reality, most of them actually are harmless. A wide variety of assassin bugs live in the Southwest. All but a few are considered beneficial, since they prey other, less savory bugs. Most would seldom, if ever, bite a human.
Assassin bugs have a long beak-like snout, which they use to suck insect or animal blood. Normally the beak is kept folded in a groove underneath the insect's thorax. If an assassin bug is touched or disturbed, it rubs the beak against its exoskeleton to make a soft chittering sound.
Only two species found in the American Southwest are known to bite humans: the masked hunter and the western bloodsucking conenose.
The masked hunter is so named because immature nymphs tend to camouflage themselves with dust and debris. The masked hunter only preys upon other insects for food, but it will bite humans in self-defense. Adults are dark brown or black in color, three-quarters of an inch long, and oblong or oval in shape.
A masked hunter will readily bite a human if it is carelessly handled or pressed against the skin. Flying hunters will sometimes bite when they land on a human.
When a masked hunter bites, it injects protein-degrading enzymes into the skin. Symptoms include sharp pain, swelling, and localized numbness. Those who have been bitten often report that it feels like a bee or wasp sting.
In the wild, the western bloodsucking conenose lives primarily in the nests of pack rats or other small rodents. During the warm summer months, it leaves the nest in search of other hosts. The bug is attracted to lights and carbon dioxide, which occasionally lead it to human habitations or unsuspecting campers.
Unlike the masked hunter, this assassin bug feeds on the blood of humans and animals. The conenose injects an anesthetic into the skin of its host as it feeds, so the bite is usually painless. It also injects an anticoagulant to ensure continued blood flow. These bugs most often bite on the hands, arms, feet, or head.
Symptoms of a bite may include localized redness, swelling, and blistering. Roughly one in fifteen bite victims experience a hypersensitive reaction to the saliva of the western conenose. More severe reactions may include nausea, breathlessness, and severe itching. Such reactions, however, are extremely rare. Only a very small handful of cases involving conenose bites in the United States require professional medical care.