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Extension Entomology

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“The Wheels On The Bus Go Round And Round” — A Rite Of The Fall Season — Wheel Bugs

–Dr. Bob Bauernfeind

This common musical refrain comes to mind each fall as BIG YELLOWS  roar back into action picking up and delivering kiddos to and from school.  Another commonly encountered fall harbinger is a large assassin bug which possesses a distinct dorsal thoracic crest:  the wheel bug.

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Actually, wheel bugs are frequently first noted in the beginning of summer.  However, they are not recognized as such due to their radically different appearance.  Wheel bug nymphs hatching from overwintered eggs are small, possess a red abdomen which is held in an elevated position, rapidly move about on long “spidery” black legs, and lack the adult’s characteristic “wheel”.  Wheel bug nymphs are the basis for reports of “small red biting spiders”.

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The proboscis is the “action end” of wheel bugs (both nymphs and adults).  Like the earlier described minute pirate bugs, wheel bugs are predators.  They use their piercing/sucking mouthpart to pierce through the integument of their prey.  During this probing process, they introduce a bit of paralytic saliva which immobilizes their prey as well as aiding in the liquefaction of internal elements which then are withdrawn.  Wheel bugs are opportunistic feeders and capable of rapid movement.  However, given the slooooow movement of caterpillars which are a known “favorite food” of wheel bugs, speed-of-capture would seem irrelevant.

Despite their reputation for inflicting a painful bite, they can be carefully handled.  It should be stated that wheel bugs are not aggressive in the sense of attacking people. If one offers a finger or a hand for a wheel bug to crawl onto, their first tendency is to shy away/hide.  However they may choose to lazily climb aboard.  Let them wander, and when tired of such, quickly flick them off.  Do not grab/hold onto them for that will invite a bite (actually, not a bite/chomp per se, but rather a defensive jab).

Just as a person can safely handle a snapping turtle by properly grasping onto the base of its tail, if one wishes to get a closer look at a wheel bug, while it is on a hard surface, use your index finger and thumb to properly grasp the wheel bug on the sides of its hardened thorax.  Use a toothpick or piece of straw to maneuver its proboscis forward, and you may see a small bubble produced at its tip —- this is the saliva which it uses to paralyze its prey (and that which causes the pain/sting on the receiving end of a defensive poke).

Another interesting feature has to do with the female wheel bug.  While in your finger-thumb grasp, as an expression of her annoyance, she may react by everting her reddish/orange anal glands which produce a substance with a distinctive odor.  This may be a defensive tactic.  It has also been suggested that it may act as a repellent offering protection to newly deposited egg masses.

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While the wheel bug is the most widely recognized assassin bug, there are many other species.

They vary in size and body shape.  While most are rather non-descript and dark-in-color (varying shades of brown or black), others can be brightly colored and patterned.  Although most prey upon insects, several species require blood meals for development and egg production.  The eastern bloodsucking conenose (Triatoma sanguisuga) is the representative species found in Kansas.  Typically feeding on a wide variety of mammalian wildlife, they have been known to also seek a blood meal from humans.  People may have heard about “kissing bugs” being responsible for transmitting Chagas Disease.  This is of significance in tropical countries where other Triatoma spp. are the major vectors.  Thus Kansans can be-at-ease.

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Wheel Bug: Be On The Look-Out For This Distinct “Bug”

by–Dr. Raymond Cloyd

If you have spent any time outdoors in the last month, you may have noticed a very distinct, grotesque looking insect on trees, shrubs, or near homes. This insect is the wheel bug (Arilus cristatus), which is common, and widely-distributed throughout Kansas and the USA. Wheel bugs, also referred to as assassin bugs, are predators that prey on insect pests. However, both the nymphs and adult can inflict a painful bite when handled by humans.

Adult wheel bugs are 1.0 to 1.25 inches long, robust with long legs and antennae, and have a stout beak and large eyes on a narrow head (Figure 1).

newFigure1WheelBugsMatingMaleonTopofFemale

 

Figure 1: Wheel Bugs Mating Male on Top of Female.
Figure 2: Wheel Bugs with Crest or Wheel on Thorax.

They are dark-brown to gray in color. The adults possess a wheel or crest with 8 to 12 protruding teeth-like structures (tubercles) on the thorax that looks like a cogwheel (Figure 2). Wheel bugs have two long, slender antennae that are constantly moving or weaving around. Females are typically larger than males. Females lay eggs that resemble miniature brown bottles with white stoppers (Figure 3).

newFigure3WheelBugEggs

 

Figure 3: Wheel Bug Eggs.

The eggs are laid in clusters of 40 to 200, and are glued together and covered with gummy cement, which protects the eggs from weather extremes and natural enemies (e.g. parasitoids and predators). The egg clusters are primarily located on the trunk or branches of trees or shrubs. The eggs hatch into nymphs that are bright red in color with black markings. The nymphs do not have the wheel or crest. The life cycle, from egg to adult, may take 3 to 4 months to complete. Wheel bugs are active day and night. They are very shy and tend to hide under leaves. The wheel bug has one generation per year and overwinters as eggs.

Wheel bugs are voracious predators and feed on a wide-variety of insects, including caterpillars (Figure 4), beetles, true bugs, sawflies, and aphids. Unfortunately, wheel bugs will feed on beneficial insects such as ladybird beetles and honey bees.

newFigure4WheelBugReadyToAttackCaterpillar

 

Figure 4: Wheel Bug Ready to Attack Caterpillar.

The mouthparts are red-brown in color and resemble a tube or straw that is located underneath the head (Figure 5) and extends out when ready to “stab” prey. Wheel bugs paralyze prey with their saliva, which contains a toxic substance that immobilizes prey within 30 seconds. In addition to feeding on insects, wheel bugs are cannibalistic, and will feed on each other.

newFigure5WheelBugsWithMouthUnderneathHead

 Figure 5: Wheel Bugs with Mouth Underneath Head.

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