2021 will go down in history for some interesting events like the historic freeze.  I admit I did not expect a plague of cankerworms to be the next hot topic, but in our current times, anything seems plausible.

My phone has been ringing off the hook this week with calls about worms all over the trees and hanging from long silk threads.  The weather is beautiful, and we are all enjoying time outside, but it’s not much fun to have a cankerworm drop down your collar or land in your drink.

Spring cankerworms are caterpillars that feed on a wide range of trees in Texas in early spring.  We usually do not notice them because the numbers are low, but periodically we get a widespread outbreak.

Cankerworms are in the moth family Geometridae and range in color from light green to brown.  These cankerworms are cool to watch for a couple of reasons.  Spring cankerworms have fewer abdominal feet than normal caterpillars, only two feet instead of three to five.  This makes them have a looping walk like an inchworm.  They also produce silk from their mouths and can swing from tree to tree or drop down to the ground.  Pretty fun way to travel by foot or by air!

Larvae (caterpillars) hatch in the spring when trees are reaching bud break.  They typically feed for three or four weeks, then drop to the ground to pupate.  Fortunately, spring cankerworm only has one generation per year, so we will not have worms raining down on us for long.

An outbreak of cankerworm can cause defoliation of trees.  A healthy tree that loses its leaves to cankerworms can generally grow new leaves without long term damage.  Trees that are stressed from drought or other problems might need to be treated with an insecticide before the leaves are stripped.

If you need to treat a serious outbreak of cankerworm on a stressed tree, Bacillus thuringiensis (Bt) or Spinosad are good insecticide options that are safe for beneficial insects and bees.  These insecticides should be used early for best control of the caterpillars.

My best advice for you to combat the spring cankerworms is to wear a hat to keep them from falling down your shirt, and enjoy this funny little caterpillar swinging from the trees.

For more lawn and garden information, contact Horticulture Extension Agent, Kate Whitney, at the Williamson AgriLife Extension Office at 512-943-3300.