The Sudden Appearance of Large Horned
Caterpillars Cause Concerns
Blayne Reed, Dr. Pat Porter, Dr. Ed Bynum
In
the past few days I have received multiple phone calls and questions regarding some
very large, horned caterpillars. This
appears to be the annual arrival of the white lined sphinx moth. I alluded to these hornworms being thus far strangely
absent from Hale & Swisher in the June 27 edition of the Plains Pest
Management Newsletter. Since that time
they have made their presence known from Hale Center to Vigo and beyond. Dr. Ed Bynum reports finding this caterpillar
north of Amarillo and Dr. Pat Porter has reports of it near Muleshoe.
As
an adult moth the white lined sphinx is also commonly referred to as the
humming bird moth or the hawk moth. The
moths are large, somewhat motley colored interesting Lepidoptera that lean toward
mimicking humming birds in behavior and body shape when in flight. There are actually several species of sphinx
moths, but these tend to be the most predominate in this area. We noted several in the area through the
months of April and May. The larva can
typically grow to be surprisingly large, up to 3 ½ inches in length, are very
plump, colored with a light green base with yellow, black, and sometimes white
markings, and a large usually yellowish spine or horn near the tip of the
abdomen. These hornworms are known to
feed on a variety of plants which include portulaca, primrose, wild grapes, and
a few types of succulent trees. Despite
a fairly lengthy list of host plants, they do appear to be very picky eaters. Over the past few years, I have noted them
mostly feeding on purslane weeds, almost completely ignoring other plants and
healthy foliage nearby.
The
massive group population and potential movement of the white lined sphinx caterpillars
can be very impressive, with many describing it as downright intimidating. These worms only seem to appear in mass
populations of at least thousands (if not by the million) with just one local generation
annually. The larva will feast on their
preferred vegetation, devouring it quickly and fully before moving to find
another pocket of that preferred vegetation with a mass migration that many
describe with a statement like, “the ground seemed to be moving and wiggling.” Meanwhile the pasture, sorghum, and cotton plants
they were near or fields they were in are left almost completely untouched with
any damage being coincidental.
Just
about all of my encounters with this hornworm over the past 15 years have ended
pretty well. The sheer number of veracious
larva of this size moving into production fields or healthy pasture is enough
to make anyone nervous and is most certainly worth keeping daily tabs on. To date, I have never been forced into recommending
treatment for these hornworms. The
fields they have infested are eventually left almost completely unscathed with
a serious hit to the weed population following either their migration away
from, or eventual pupation of the larva.
I can state with some confidence this pattern of nerve racking benefit
to production fields should continue this season. I cannot be nearly so certain of a
respectable outcome of this hornworm’s impact to a grape vineyard or garden
plot, horticultural or vegetable. There
is likelihood that something within those situations could be what the white
lined sphinx moths picky diet would find delicious.
If
treatment for these hornworms becomes necessary it is believed a good general
pyrethroid would do a good job of achieving control. Thus far, there has not been a need for an
efficacy trial in this region so this assumption has not been verified.
Please call or come by with any
questions,
Blayne
Reed
