Wednesday, July 20, 2011

The Wheel Bug Emerges

I came home today to the most wonderful surprise I've had in a long time:

Arilus cristatus, the wheel bug, in all of its salmon-colored glory.

For those of you who aren't familiar with my love of this particular insect, the wheel bug is my absolute favorite insect. Why? To list a few reasons, it's an assassin bug, it's the largest terrestrial true bug (Order Hemiptera) in North America, and it has that ridiculously interesting cogwheel protuberance on its pronotum. This bug is unique and when you see it, you know what it is and that you shouldn't test its patience.

The fresh new bug on the left, with its out-of-style skin on the right.

Anyway, what we're actually looking at here is the wheel bug right after it has molted out of its 5th instar. Wheel bugs go through a nymph stage of life with five separate growth periods (instars), and it sheds its skin between each period, growing as it does so. At the end of its fifth instar, it has finished its nymph stage and emerges as a fully-formed adult: with wings and its characteristic cogwheel. This wheel does not appear in any of the nymphs. If you're lucky and can catch the wheel bug soon after it has molted its final larval skin, you're in for a treat. It emerges as a beautiful red/pink/orange color....let's call it salmon. 

The wings still have a leathery sheen to them, and are clear enough that you can see the white and red-striped abdomen.

Unfortunately, this salmon color doesn't stick around forever, and fades to jet black within a few hours. Though I suppose in the long run, it's better for camouflage reasons. It's not as striking as the red of course, especially after its yellowish-gray pubescence overtakes its body, but it's functional.

If you want more information on wheel bugs, you can check out a previous post of mine here. 


  1. Very cool, Derek! I never knew they went through so many stages and came out such a unique and interesting color. Hard to imagine if humans had a growth cycle similar to that; leaving a shell of old skin behind every year or so.

  2. Every time I think about a bug's life cycle I try to imagine what that would be like, but it's just so foreign! Especially in a caterpillar's transition to a butterfly...they have most of the organs and everything rearranged even before they enter the cocoon! That's like transforming all your organs into other organs, all while going about your daily life as normal. It wrinkles my brain, it's so interesting.

  3. Derek - the darkness that develops is caused (in part) by sclerotization, the process in which the newly laid chitin is cross-linked. This makes it much tougher, and thus is a good thing for the bug. Other insects are white just after a molt; the wheel bug must have some red pigment in the body, perhaps in the hemolymph.

  4. I have never heard of a wheel bug but today we had the experience of seeing one come out of the fifth instar -- how cool. I have photos but not sure how to post


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