Only Mother Nature and the wheel bug know the function of the wheel.
For those who dwell in the mid-Atlantic region of the United States, the brown marmorated stink bug has become an inimitable pest attacking apples, vandalizing vegetables, sullying soybeans, and invading homes. Since its discovery near Allentown, PA in the 1990’s, it has caused millions of dollars of damage to a wide variety of crops. This scalawag has delivered distress to millions of homeowners in more than 33 states by entering dwellings to escape the ravages of wicked winter. For those of you who have had enough of this rascal, this month Bug of the Week visits several natural enemies that know how to give stink bugs the ultimate comeuppance. Last week we enjoyed the curious reunion between the Chinese praying mantis and the brown marmorated stink bug. In this week’s episode, we introduce the stink bug to another awesome predator native to North America, the wheel bug.
Baby boomers may fondly recall a regular feature of Mad Magazine called Spy vs. Spy where two pointy-nosed secret agents attempted to outwit and undo each other. In this week’s episode, we meet the entomological equivalent in Bug vs. Bug. The brown marmorated stink bug and the wheel bug both belong to a clan of sucking insects known as the Heteroptera. The wheel bug is a species of assassin bug and, as the name implies, it kills other insects. On a recent foray to study stink bugs in a nursery, our bug-hunting students encountered record numbers of the wheel bug, Arilus cristatus. The common name, wheel bug, stems from the fact that this terror has a structure on its back that looks like a spoke-bearing medieval torture device. The function of this wheel is known to Mother Nature and the bug, but not to me.
Gorgeous wheel bug nymphs cluster near eggs from which they hatched before venturing off to find prey.
The business end of the wheel bug is the powerful beak, or proboscis, stored between the beast’s front legs when it is not in use. Upon spying a tasty morsel, the wheel bug cautiously approaches, embraces the mark with long front legs, and then impales the victim with its powerful beak. The wheel bug pumps strong digestive enzymes through the beak into the prey. These enzymes liquefy the body tissues of the hapless victim. A muscular pump in the head of the bug slurps the liquefied meal up through the beak. Young wheel bugs use protein from their prey for growth and development and adult females convert prey into eggs. In autumn, the well-fed female wheel bug lays barrel-shaped eggs in clusters of several to more than one hundred, usually on the bark of a tree. Eggs hatch the following spring in May and June. Small wheel bugs, called nymphs, are magnificent creatures with bright red abdomens and orange antennae. They dine on a wide variety of insects including caterpillars, sawfly larvae, beetles, and other bugs.
In most years, I feel lucky if I witness a half dozen of these monsters at work in the wild. However, with plant nurseries and landscapes laden with stink bugs, it is not unusual to see scores of wheel bugs stealthily stalking and assassinating their stinky marmorated cousins. How much benefit results from greater numbers of these assassins remains to be seen, but we hope that these and other naturally occurring predators and parasites will stem the onslaught of brown marmorated stink bugs.
With the wheel bug's beak firmly inserted behind its head, this brown marmorated stink bug prepares to journey to the great beyond.
If you encounter wheel bugs, please heed this caution. While holding and admiring one wheel bug, I learned firsthand, so to speak, that the wheel bug could deliver a memorable, painful poke with her beak! If you keep wheel bugs as pets, beware: try not to handle them directly or you too may become the victim of this clever assassin.
References
Many thanks to Ashley, Nancy, Chris, Ryan, Erik, Caroline, and Chris, for wrangling the stink bugs and wheel bugs that inspired this episode. Support for our research on BMSB comes from USDA-NIFA SCRI Award #2011-51181-30937.
To learn more about wheel bugs, please visit the following website:
http://entnemdept.ufl.edu/creatures/trees/wheel_bug.htm