A mega hatch of Genista larvae on transplanted Texas Mountain Laurels along the Llano River created an uncomfortable “caterpillar quandary” for me this weekend.

Sophora worm, genista moth larvae

Not cool. Hundreds–no, thousands–of these Genista moth larvae, devoured our Mountain Laurels. Photo by Monika Maeckle

It was an odd day, digging up wild parsley in search of chubby, Eastern Swallowtail caterpillars for fostering and fun at home, followed by hours of trying to figure out a humane and responsible way to kill hundreds–no, thousands–of unwelcome critters decimating several precious Mountain Laurels.

The culprit:  the Genista Broom moth caterpillar, Uresiphita reversalis.   Sometimes called the Sophora worm, these moth larvae relish the toxic leaves of our native Texas Mountain Laurels, Sophora secundiflora.

We have painstakingly imported several of the gorgeous native evergreens to our stretch of the Llano, digging difficult holes for transplanting them in the Hill Country caliche and watching the slow growers progress over the last 10 years.  Mature Mountain Laurels are expensive at nurseries.  They serve as a harbinger of spring with their Kool-aid scented purple blooms, which alert us that ground temps have warmed, vegetables can be planted, and summer will be here too soon.

Genista Broom Moth, photo via http://wildflowers.jdcc.edu

Genista Broom Moth, photo via http://wildflowers.jdcc.edu

First I tried picking them off by hand.   Then I fetched a sheet from the ranch house and shook the bushes, watching as they fell by the dozens to the ground.   Finally I got a hose and blew them away with a high pressure jet of well water.    Those handpicked and retrieved from the sheet went into a jar that was placed in the freezer for a relatively painless death.

Texas Mountain Laurel, always a harbinger of spring in the Hill County Photo via Ladybird Johnson Wildflower Ctr.

Texas Mountain Laurel, always a harbinger of spring in the Hill County.  Blooms form on second year growth.                 Photo via Ladybird Johnson Wildflower Ctr.

I felt bad. But my Mountain Laurels were decimated.  Genista larvae favor new growth and eat the buds and terminals of the Mountain Laurel first.  And that’s where the purple flowers form in the spring.  Interestingly, I had never noticed the abundant caterpillars in 20 years in Central and South Texas.

“They’re always around,” said Elizabeth “Wizzy” Brown, an integrated pest management specialist for Texas Agrilife Extension Service in Austin, dismissing my theory that something special was going on.   I read somewhere that Genistas are poisonous to birds, and speculated that perhaps that’s why they were left seemingly untouched by avian species.   Brown dismissed that.

She recommended BT- bacillus thuringeisis, the organic biological pesticide and all- around caterpillar killer.   When I let her know I garden for butterflies and moths–just not THIS moth–she suggested getting out the vacuum cleaner to suck them off the tree.  Wish I had thought of that.

Genista moth caterpillars desinted for the freezer

Sorry, fellas! You’re history.            Photo by Monika Maeckle

Entomologist Mark Muegge, a Texas Agrilife butterfly expert out of Ft. Stockton, felt the pain of my “squish remorse.”

“I understand….I’m kinda the same way,” he said.  “Sometimes you have to use tough love.”

“They’re not a particularly attractive moth or caterpillar,” sniffed Mike Quinn, an Austin entomologist and founder of the useful Texasento.net website.   “There’s no aesthetic reason to not squish them. They’re a pest.”

Brown and Muegge both proposed that the Genista Broom moth’s purpose in the universe is to supply fodder for the food web.

Lizards eat them, the brilliant tachinid fly uses the Genista as a host, laying its eggs on the caterpillars, eating them from the inside out, and wasps also consume the Genista as food.  “They fit into the food web,” said Brown.

“Everything has its purpose,” said Muegge.  “What they’re good for is hard to say.”

According to Muegge, my reaction to the onslaught of caterpillars may have been extreme, an embarrassing admission for a butterfly evangelist.
“I have never seen a tree or shrub die from being defoliated,”  he said.  “They’ll stress, but they’ll come back.”

And, fortunately or not, so will those caterpillars.

More posts like this:

Like what you’re reading?  Don’t miss a single post from the Texas Butterfly Ranch. Sign up for email delivery in the right navigation bar on this page, like us on Facebook, or follow us on Twitter, @butterfly beat.