Insects that belong to the Hemipteran family Reduviidae are collectively known as assassin bugs. The family includes over 160 species in North America, and all are meat-eaters.
The common name for the family clearly describes how these stealthy hunter-killers make a living. Both the adults and immatures (nymphs) are effective predators. They have exceptional eyesight with their bulbous compound eyes providing an almost 360-degree field of vision; all the better to see you with!
Their raptorial front legs are designed for grabbing and holding prey. Once the assassins grasp their prey, their piercing-sucking mouthparts that are housed in a structure called a beak swing (literally) into action to inject paralyzing and pre-digestive enzymes into prey which is most often another insect. They then suck the essence-of-insect from their hapless victims.
Rapacious assassin bugs in the genus Zelus gain additional grabby assistance in the form of a sticky goo covering their front legs. The gluey material is produced glands on their front legs making them function like sticky fly paper. You may find the Pale Green Assassin Bug (Z. luridus) hanging out on flowers waiting to grab a quick meal with their sticky legs.
The cryptic coloration of the pale green assassin bug can make this predator difficult to spot. However, the opposite is true for the appropriately named Orange Assassin Bug (Pselliopus barberi). Their gaudy color motif makes the adults and nymphs easy to spot as they hang out on flowers during the summer in the hope of snagging a meal. The 1/2” long adults spend the winter in protected sites including beneath tree bark. They are commonly seen on tree trunks in the early spring and fall.
Our native Wheel Bug (Arilus cristatus) is one of the largest and most common types of assassins found patrolling trees and shrubs in Ohio. Indeed, wheel bug immatures (nymphs) currently dominate the assassin scene in our state. However, as with most assassin bug species, wheel bug nymphs look nothing like adults.
The adults are called wheel bugs because of a peculiar feature that rises from the top of the bug's thorax. The structure looks like half of a cogwheel, with the gear teeth clearly visible. Wheel bugs are big, measuring over 1 1/4" long, and their color varies from light gray to bluish-gray to grayish-brown. The adults will appear in Ohio later this season.
Wheel bug nymphs hold their curved abdomens upright as they parade around on their long, spindly, spider-like legs. The nymphs are often mistaken for spiders. Of course, insects have six legs and spiders have eight.
Caterpillars and sawfly larvae are favored table fare of these voracious predators; however, they will not turn their beaks up at other arthropod meat morsels. Many of the images in this Alert were taken of wheel bug nymphs patrolling an English oak (Quercus robur) heavily infested with Oak Lecanium Scale (Parthenolecanium quercifex, family Coccidae (Soft Scale Insects)). The infestation was the focus of a BYGL Alert earlier this season [see Oak Lecanium Scale is Producing Sticky Oaks, May 22, 2022, https://bygl.osu.edu/node/1972 ].
I observed several nymphs with their beaks stuck into the lecanium scales although I wasn’t successful with photographing them in the act. I did mention the bugs have excellent eyesight! I’ve never observed assassin bugs feeding on soft scales before. However, their prey selection isn’t surprising given that soft scales are stuck to stems and can’t move which makes them an easy target. Of course, their soft shells are no match for bug’s beaks, and the soft scales no doubt offer a protein-rich delicacy to the developing assassin nymphs.
A word of caution: do not handle wheel bug nymphs or adults. They are beneficial insects because they are predators. However, they are also known to use their piercing-sucking mouthparts to nail the probing fingers of uniformed gardeners! All members of the family are capable of delivering a painful bite to people. The pain of an assassin bug bite has been described as being equal to or more powerful than a hornet sting, and the wound may take over a week to heal. It is best to appreciate these bio-allies from afar.