Sunday, August 12, 2012

Stinging Discovery in Our Redbud Tree

Stunningly beautiful,
stunningly painful

I jerked the loppers out of the branch and leaves of our ‘Forest Pansy’ redbud tree (Cercis canadiensis) in an involuntary reaction to a searing stinging on my right wrist.

Wasp?  Bee?  Hornet?  It hurt like no other sting I could remember.  I looked at my wrist—which was rapidly turning red.

Then I looked at the undersides of some of the redbud leaves and discovered scores of brightly colored, hairy caterpillars—black with almost phosphorescent yellow spots and some orange at both ends.

My wrist was hurting so badly that I did something unusual.  I went inside and told Ellen that I had been stung and asked that she keep an eye on me for awhile.  She looked at my wounds and suggested I take a Benadryl tablet or two, but I was more interested in getting a better look at my assailants.

I went outside with my camera, finished lopping off the storm-damaged redbud branch, and took some photos of the stinging caterpillars.

Back inside later, I looked at the caterpillar section of my insect book—and didn’t find any photo remotely similar to the redbud critters.  My sting in my wrist continued for several hours and then gradually went away.  The redness seemed to lessen too.

I wrote a sentence or two telling my story and sent several photos to the University of Maryland Extension and asked for help identifying the caterpillars.

“These are white flannel moth larvae,” answered Stanton Gill.  “We usually don’t see these until the end of August.  Everything is early this year.”

“Sorry to hear about the stings,” replied Mike Raupp.  “These are larvae of the white flannel moth, Norape ovina.  In addition to the redbud, they eat leaves of many other woody plants.”

How do the caterpillars sting?  “Stinging caterpillars do not sting in the manner of bees, yellow jackets, and wasps,” writes Lacy L. Hyche, in “Some Stinging Caterpillars on Shade and Ornamental Trees” (Highlights of Agricultural Research, 1997). “Females of the bee-wasp group … have stingers with which they penetrate skin and inject venom. Stinging caterpillars have no such stinger, but bear instead specialized nettling or urticating setae (hairs) or spines. These structures are hollow and contain toxins produced by poison-gland cells to which they are connected. The sting of the caterpillar results from contact, usually inadvertent, with toxin-bearing setae or spines.” 

A day after my encounter with the caterpillars, the pain was gone, the redness was going away, but then I noticed a patch of blisters on my wrist where the caterpillars had stung me.  If I hadn’t known the cause, I might have thought I had a bad reaction to poison ivy.

You can be sure that the next time I need to prune a broken redbud limb in late summer, I’ll look first for stinging caterpillars before I start cutting with my loppers.

Here’s a photo of an adult white flannel moth.

Here’s a link to the University of Maryland Extension’s “TPM/IPM Weekly Report” (August 10), which chronicles reports of insects and diseases affecting Maryland landscape plants.