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 While enjoying our time outdoors, we often
encounter various insets we may not have seen or noticed earlier in
the growing season. One such insect is the unusual, and to some
scary, looking wheel bug.
What do they look like?
Adult wheel bugs (Arilus cristatus) are large (1 to
1-1/2 inches long) light gray to grayish-brown distinctive-looking
insects. They get their name from the prominent cog-like toothed
‘wheel’ on their thorax (there can be 8-12 teeth/tubercles on this
wheel). They are the only insects in Illinois (or the U.S.) to have
such a structure. They also have beak-like mouthparts that arise
from the front of their head, which some think resembles an
elephant's trunk.
The nymphs are red and black when they first hatch. Later instars
(stages) lose the red coloring, becoming black and gray. Unlike the
adults, the nymphs do not have a ‘wheel’ on their thorax. This does
not develop until they reach adulthood.
What do they do?
Wheel bugs are a type of assassin bug (family Reduviidae), so they
are predators. They have raptorial front legs (like praying mantids)
that they will use to grab prey. Once they have captured their prey,
they insert their mouthparts into their prey and inject their
saliva, which contains chemicals that paralyze the prey and begin
digesting it. They will then suck out the ‘juices’ of the insect,
like drinking a juice box. They are
generalist predators, meaning they will feed on a wide variety of
different insects. They can commonly be found feeding on pests like
caterpillars, beetles, sawfly larvae, aphids, and stink bugs, among
others. In fact, wheel bugs are one of the few insects that will
feed on the invasive brown marmorated stink bug. [to top of second
column] |
Because they are generalist predators, they may also feed on insects
we would consider beneficial, such as honey bees and wasps. However,
the benefit of their feeding on pest insects far outweighs the
occasional beneficial insect that may be eaten.
Why are we seeing them now?
While we can find wheel bugs throughout the growing season (eggs
hatch in spring), we commonly overlook the smaller nymphs. The
nymphs will begin maturing into adults from mid-summer to fall. The
larger, more impressive-looking adults catch our eyes much better
than the nymphs do.
Adults are often attracted to lights at night, bringing them close
to our homes, where they will search for prey. They are also on the
move this time of year, looking for potential mates as well as
places to lay their barrel-shaped eggs (usually on trees and shrubs)
Do they bite?
Because of their large size and intimidating appearance, people are
often concerned that they may pose a threat. While wheel bugs are
not aggressive and avoid contact with humans, they will defend
themselves (bite or, perhaps more accurately, stab) if harassed or
handled.
Their bite has been described as being as bad or worse than a sting
from a wasp or hornet. After the initial pain of the bite, which can
last for several minutes, the area may be numb for several days, and
it may take a few weeks for the wound to heal.
While they may look dangerous and pack a painful bite, remember they
aren’t aggressive or out to get you, and they help control pests.
Good Growing Fact of the Week: Like their stink bug cousins, wheel
bugs will release an unpleasant chemical when disturbed, although
not as potent. [SOURCE: Ken
Johnson, Horticulture Educator, University of Illinois Extension]
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