A Wheel Bug, an assassin bug, hangs out on a bronze fennel, which is the home of one of his favorite meals -- Black Swallowtail Caterpillars. This is a young Wheel Bug, which hasn't yet formed the characteristic wheel protrusion on its back.
Every day, I watch the progress of the Black Swallowtail (BST) caterpillars on my huge bronze fennel plant, which is home to a lot of other insects, including this character (see photo) who seemed to be hanging out and doing nothing while sitting on a fennel flower. Very suspicious. I thought he was up to no good. He gave me this look that said: “Hey, Lady, Don’t look at me. I’m just minding my own business.” Yes, exactly. What was his business? What did he eat? He wasn’t sipping flower nectar like the bees and wasps and occasional butterfly. I confess after a couple of days, I gave the fennel a shake and this bug tumbled to the earth. The next day I saw him slowly making his way back to the top. I don’t know how much I should interfere to protect “my” BST caterpillars. Was this a “good” bug or a “bad” bug?
I emailed Monarch Watch at the University of Kansas about this bug. Jim Lovett replied: “Looks like an immature wheel bug to me (Order: Hemiptera; Family: Reduviidae)…if you’re not familiar with this bug be sure to check out some images of the adult. It’s a neat little critter that always captures people’s attention – “little” of course is relative; adults wheel bugs can be 1.5 inches long. They use that piercing/sucking beak to puncture their prey (and can inflict a painful “bite” on us humans if mishandled). FYI – all hemipterans (the “true bugs”) have piercing/sucking mouthparts.”
I asked whether this bug would eat a BST caterpillar.
Jim’s answer: “Yes, it would. It is a common predator on caterpillars (and other soft-bodied insects) of all sorts.”
Here’s a link Jim suggested: Wheel Bug. The Wheel Bug is the largest member of the Assassin Bug family and is related to stink bugs. Mean and smelly! But useful, too, because they eat a lot of damaging caterpillars.
The next day, the Wheel Bug disappeared and so did a few of my smaller BST caterpillars. I hope Mr. Wheely didn’t eat my caterpillars!
To learn more about butterflies and caterpillars, click on Monarch Watch. My most recent post on raising BST and Monarch caterpillars is here: Survivor — Caterpillar Version.
Catherine Sherman 
Interesting post..I once opened a box of flowers from South America only to find an assassin bug, that looked like a reptilian dinosaur creature. I contacted the University of Washington, and took pictures of him and then after much research found out that he was a nasty bug. Someone in the shop flicked him off me, and I was a little mortified to find out that this little bug had a habit of spitting and that if it lands in your eyes it causes blindness. Yikes..not to fond of that bug after that. I’m always careful now opening boxes of flowers that come from out of the country, my big fear is that I may find a coral snake or some other snake with venom because Miami is the inspection point for flowers from South America and other locations. Thanks for the great post.
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I’ve seen how protective you are about your BST caterpillars, but this is the first time I’ve heard about an Assassin Bug. Now that you’ve got this bug’s number, I’m putting my money on you.
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Wheel Bugs! Caterpillars! Larvae! What’s this world coming to? When I was a kid, growing up in Tunguska County, we didn’t have any such creatures as those. Why, after the great meteor explosion of 1910, there weren’t even any trees, grass or bushes around where I lived. My folks used to show us pictures from National Geographic about big cats, zebras and the like, but we didn’t really believe they existed. Are you sure these aren’t some kind of government experiments gone awry? A. T.
Is Tunguska County near Area 51? I don’t think the government could up with anyone so perfect as the Wheel Bug. I took an inventory of my caterpillars today, and there are none left, as far as I can tell. Only two so far (not counting Reggie) have reached the size to head off to pupate. It’s a sad life being a caterpillar rancher. Cathy
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My daughter discovered two wheel bugs in our garden last fall. We find them fascinating and helpful for our garden, but I can understand the frustration of them eating all your caterpillars!
I even made a little info sheet on them if you would like to read more.
Click to access wheel-bug-minibook-and-info.pdf
-Aadel in KS
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