This creature looks like something from the movie Jurassic Park and gardeners often wonder if it is real. Arilus cristatatus, commonly known as the Wheel Bug is a voracious garden predator and is classified as a beneficial insect. It gets its common name from the prehistoric looking wheel shaped armor on its back. This is the only North American insect with this peculiar anatomy. The function of this wheel is not known, but it may alert insect eating animals and birds that it tastes as bad as it looks, or possibly so the insect can identify a mate, although both males and females have the wheel. It also has a distinct aroma that is produced from scent glands on its abdomen that warns potential predators that it is unpalatable.
It is one of the largest true bugs in North America, with the bodies reaching as long as 1 1/2" or 38mm and belongs to the family Reduviidae, which includes a number of assassin bugs. Assassin bugs are noted for their predatory habits, as they stalk their prey and quickly pounce upon the hapless victim. They inject a powerful poison from their ‘fang' called a rostrum and the substance liquefies the internal organs of the unlucky captive. The wheel bug then sips the resulting goo from the shell of its prey. This sounds like the plot of a horror movie, but sometimes nature is more frightening than fiction. Gardeners are cautioned not to handle or disturb this insect, as its bite is painful and often described as worse than a hornet sting, sometimes resulting in a scar. One report goes as far as to compare it to a snakebite, although the pain didn't last as long. It is safe to assume that they wouldn't make the best pets. Its range is widespread and reports from all across the US and Mexico let us know that it can survive in a wide range of environments.
There is only one generation a year and new wheel bugs hatch out each spring from eggs that have overwintered. The female attaches the small, barrel shaped eggs to twigs and branches in the fall where they spend the winter. It takes roughly 100 days for the nymphs to go from hatchlings to adults, so most often the adult insects are spotted in late summer. Nymphs go through about 5 different instars (or stages) and do not get their 'wheel' until mature. The small nymphs are also highly predatory and feed on aphids and small caterpillars. While not necessarily nocturnal, you may notice them at night because some of their favorite prey is attracted to the lights over your garage or front porch.
Before you decide to systematically execute any wheel bugs you may find in your garden, note that some of their favorite foods are Japanese beetles, aphids and tent caterpillars. However, they don't tend to be very picky and nymphs have been known to attack and eat each other and females often consume the male after mating much like the praying mantis does. They are also one of the few insects that will take on a full-grown praying mantis and win. However, they aren't aggressive toward humans and move slowly, so as long as you let them go about their business, they'll leave you alone. They can fly, but it is a clumsy process, so they prefer to walk and will even climb trees to search for prey. They walk with a jerky, mechanical stride that looks somewhat robotic and when they fly, their wings make a similar noise to a grasshopper flying. All in all, they are an excellent representation of what a Steampunk insect would look like, or possibly something from 60 million years ago. Its grayish-brown coloring blends well with tree bark and leaf litter, so they are easy to overlook.
Arilus cristatatus is found in North America from Rhode Island to California, but there are 4 recognized species of Arilus world-wide with similar habits. Tropical cousins in the subfamily Triatominae, known as kissing bugs, prefer the blood of vertebrates. This not-so nice member of the family carry parasites that cause Chagas disease, a tropical illness that can be fatal if not treated. The North American wheel bug is shy and so well-camouflaged that many people have never seen one. They do not exist in great numbers and chances are you'll never see more than one or two in a season. If one appears in your garden, simply let it proceed about is business of eliminating the pest insects. Consider it free, organic pesticide. You might want to capture and relocate any you discover near where children play as they are interesting enough to get the attention of a toddler and the bite could cause a lot of distress for both the child and adult involved.
Images courtesy of BugFiles