Amazing Assassins

By Eric R. Eaton | June 2, 2003
From Missouri Conservationist: Jun 2003

Missouri sportsmen could learn a lesson in patience and stealth from assassin bugs. Some wait for victims in daylight, while others hunt a midnight snack. Some may even be stalking YOU! Most prey on other insects, but two of Missouri's nearly 40 species feed on blood.

You can rightly call assassins "true bugs," members of the order Hemiptera. True bugs resemble beetles or roaches at first glance, but a closer look reveals important differences. The front pair of wings is leathery at the base, but membraneous in the outer half. At rest, they cross over the insect's back in an X pattern. These bugs have piercing-sucking mouth parts, too.

Assassin bugs are further segregated into the family Reduviidae (Reh-deu VIE-i-day), with roughly 5,000 species worldwide. Their distinguishing feature is a groove on the insect's "chest," into which the short, stout beak folds when not in use. Tiny ridges run across this channel, and the bug can make a squeaking noise by rasping its beak across those ridges.

It is difficult to generalize beyond anatomy, but the wheel bug, Arilus cristatus, is a model of the typical assassin's life cycle. These 1-inch long insects get their name from a cog-like crest on their mid-section. By day they prowl slowly about trees, bushes and flowers, but strike prey with lightning speed. They can overpower insects many times their own size and weight. Pinning a victim with their front legs, they kill it almost instantly with an injection of toxic saliva. The potent cocktail of enzymes they deliver to victims approaches snake venom in virulence, dissolving the internal tissues into a soup that is sucked up by the wheel bug. A wheel bug may bite in self defense, too, or deploy red-orange scent sacs from its rear end.

After mating in the fall, female wheel bugs lay brown, bottle-shaped eggs in hexagonal clusters of 40 to 190. They cement them to tree trunks, fence rails, and other surfaces. Eggs on the periphery are vulnerable to tiny wasps that lay their own eggs inside them.

Those that survive hatch in early May. The nymphs lack wings, crests, or obvious sex differences. They go through five nymphal stages, each slightly larger than the last. To reach the next stage, they shed their exoskeleton, the skin-like outer cuticle. This process is called molting.

By early July, most larvae reach adulthood. They finally sport a crest and wings, and their gender becomes evident. Females are larger and have wider bodies than males.

Some of Missouri's assassins pass the winter as adults rather than eggs. Pselliopus barberi is a half-inch insect colored Halloween orange with black speckles. It hibernates under rocks or bark or in logs, sometimes in large groups. It turns up on foliage and flowers in the spring and fall.

Stop to smell the flowers, and you may come nose-to-nose with the spined assassin bug, Sinea diadema. Fortunately, people are not on its menu. It is a valuable predator of several kinds of plant-eating insects. Spined assassin bugs produce two generations per year and are common on goldenrod in the fall. Their brown color, rugged body shape and spiny legs let them pass for bits of dried-up leaves.

An even more convincing disguise is that of ambush bugs. Phymata fasciata and P. vicina are practically animated blossoms. At only one quarter of an inch, with squat bodies and cream, yellow or pale-green color, they blend seamlessly with wildflowers in all stages of budding and blooming. Even during courtship and mating, when the males ride piggyback atop females, their camouflage remains uncompromised.

Until recently, ambush bugs were placed in their own family, the Phymatidae, due in part to their unusual, vise-like forelegs that they use for grabbing prey. They routinely tackle butterflies, large wasps and flies, but sometimes they get greedy. I once saw one seize a hovering bee, only to be yanked off its perch when the bee retreated.

Young bee assassins, Apiomerus crassipes, are also ambush hunters, but the large, robust adults pursue prey from flower to flower. Black with red trim, they advertise their own distastefulness to predators. Sticky hairs on their front legs help them secure struggling prey. Look for them in open woodlands in June and July.

Our two species in the genus Zelus also have tacky legs. They are slender and lanky, pale green or brown, and more common on foliage than flowers. The males of at least one Colombian species guard their eggs against parasites, but our domestic varieties don't exhibit this behavior. Both sexes are beneficial predators of crop and garden pests.

Perhaps the most bizarre assassins are the thread-legged bugs. There are at least four Missouri species. All are extraordinarily thin, with stilt-like walking legs and front legs similar to those of a mantis. Most are only one half to three-fourths of an inch long, but Emesaya brevipennis is a giant at an inch and a half. All can be found skulking around barns and other old buildings. Some species lurk at the edge of spider webs, and may even enter the snares to steal the spiders' prey.

When darkness falls, turn on your porchlight. You will be introduced to the night shift, as well as some wheel bugs putting in overtime. The dinner crowd may include Narvesus carolinensis, a light brown creature with a single black spot on its back. Stenopoda cinerea is a large, leggy, straw-colored species. The big, stocky Microtomus purcis is a spectacular combination of black, white, and red. Rasahus hamatus, one of the "corsairs," can inflict an excruciating bite if provoked. Nearly an inch long, it is glossy brown with black markings and has prominent pale spots on its black wing membrane.

Among the more abundant visitors are "kissing bugs," a name applied to at least three Missouri species, including Melanolestes picipes. Known correctly as the black corsair, this bug is uniformly black and about three-fourths of an inch long. A relative, M. abdominalis, is black with red trim.

Females of both types are often wingless and run rapidly over the ground, hiding under stones and boards by day. Males fly well and sometimes alight on people.

Resembling little ankle weights are the fossa spongiosa, special pads that help the bug grip prey and climb slick surfaces. A population boom of the black corsair caused the "Kissing Bug Scare of 1899" in the northeast U.S. Bugs invaded houses and bit residents who slapped or crushed them.

An even stranger kissing bug is the masked hunter, Reduvius personatus. Native to Europe and north Africa, it was accidentally introduced to New York City and has since spread across much of North America. It is not common, but can stray indoors where it feeds on bed bugs, carpet beetles, flies and other insects.

The adults are winged, dark brown or black, and an inch long. Females drop eggs singly, in dusty corners and other undisturbed spots. The larvae are covered with sticky hairs, and they conceal themselves in lint, dust and other debris.

Outdoors, masked hunters are often associated with cliff swallow colonies, feeding on swallow bugs, relatives of bed bugs. People bitten by masked hunters experience nearly intolerable pain and swelling, and, in the worst cases, may vomit and faint.

One bite you should definitely avoid is that of the blood-sucking conenose. Two species occur in Missouri: Triatoma sanguisuga and T. lecticularia. These are kissing bugs in the truest sense, sometimes drawing bloodmeals painlessly from the faces of sleeping humans. An inch long, oval, and very flat, they are easily recognized but seldom seen. They live and breed in the nests of wood rats, their normal hosts. Instead of the normal five nymphal stages, conenoses have eight, and can take up to three years to mature. They require at least one bloodmeal (usually several) to graduate from one stage to the next. Adults fly only briefly, to find mates and disperse, at which time they are attracted to lights.

From Mexico to Argentina, Triatoma and its relatives rank among the deadliest of insects. They frequently carry Chagas' disease, caused by a one-celled organism similar to the one responsible for African sleeping sickness. Armadillos and possums are common reservoirs of this pathogen. Oddly, the conenose does not transmit the parasite in the course of feeding, but when it defecates, expelling the microbes in the vicinity of the bite. Victims infect themselves when they scratch the feces into the wound, or then touch their eyes or other mucous membranes with contaminated fingers.

A quirk in the behavior of U.S. Triatoma helps explain the absence of Chagas' here. Our species leave their victims before excreting wastes. If only the others could be toilet trained! Chagas' afflicts an estimated 7 million people annually, of which 10 percent may die. The highest incidence is among the rural poor who sleep in thatched-roof huts among their domestic livestock.

A "normal" conenose bite usually leaves a welt or fat lip the following morning. Itching, burning, redness and blistering are not uncommon. Serious side effects can include heart palpitations, nausea, faintness and shortness of breath.

Unfortunately, Chagas' disease is subtler in its initial manifestations. A one sided swelling of the face or eyelids, followed by fevers, may be the only symptoms. Most victims are unaware of their infection for 10, or even 20 years. By then, irreparable lesions have developed in the nervous system, heart and digestive tract. Some say Charles Darwin contracted the disease during his epic voyage on the HMS Beagle, eventually succumbing to it years later.

Avoiding our harmful assassins involves taking simple precautions. Exclude them from your home by repairing window screens, applying weatherstripping, and sealing other openings. Use yellow bulbs in porchlights, and dispense with bug zappers. Do not camp or sleep inside caves, barns or other sheltered areas frequented by masked hunters, corsairs, and conenoses. To avoid a self-defense bite, gently brush away any bug that lands on you.

The beneficial qualities of assassin bugs far outweigh their negative potential, and learning to get along with these indispensable predators is in our own best interest.

This Issue's Staff

Editor - Tom Cwynar
Managing Editor - Bryan Hendricks
Art Editor - Dickson Stauffer
Artist - Dave Besenger
Artist - Mark Raithel
Photographer - Jim Rathert
Photographer - Cliff White
Staff Writer - Jim Low
Staff Writer - Joan McKee
Circulation - Laura Scheuler