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The Caterpillars are Falling! (J. Moll – 3/22/17)

Each spring the cry rings out, “The caterpillars are falling out of the trees!”  These menaces are tussock moth caterpillars.  They drop down like rain from oak trees.  Besides the annoying presence of numerous hairy caterpillars, these insects may spin their difficult-to-remove cocoons on houses, boats, picnic tables, slow moving pedestrians and other outdoor items. Hatching occurs during late February and early March, at the same time oak trees are beginning to leaf out. The newly hatched caterpillars move from the egg mass in search of newly expanding spring leaves so they can feed on them. Once the caterpillars start falling out of the trees by the hundreds, they are by and large done with the oak trees.  They have been feasting for several weeks on the tender new leaves.  By the time they fall on your head they have finished feeding and are now completing their life cycle.

Should the gardener worry about these caterpillars while they are still feeding on the foliage of the oak trees?  Caterpillars that feed on mature oak trees have little effect on the overall health of the tree. Large trees retain enough energy to put out a second flush of new foliage with no permanent damage to the tree.  It is difficult and nearly impossible to spray large trees with insecticide.  Therefore spraying big trees is really a waste of money and is unnecessary.  Small trees, on the other hand, may need your help.  Your smaller trees and shrubs could be defoliated if a wind-blown caterpillar happens to land on them. If the tree is small enough, handpick the caterpillars and drown them in a bucket of soapy water for quick, easy and inexpensive control.  Nature provides plenty of natural caterpillar predators like birds and predatory wasps.  When the predators can not keep up with the caterpillar population, control can be obtained with the natural insecticide B. T., sold under the trade names Dipel® and Thuricide®. This product offers excellent control and is harmless to the caterpillar’s natural enemies.  The caterpillars must ingest this product, so they have to still be feeding on the foliage for effective control.  By the time they are falling out of the trees it is too late to spray them.

Another annoyance created by the caterpillars is the cocoons they spin.  Walk around the house with a broom and sweep the climbing caterpillars into a pail of soapy water before they have a chance to spin their cocoons. Remember, they are not eating anymore, so spraying them with insecticide is useless. Spraying them off with a hose will just waste a lot of water.  Should a few make cocoons in unwelcome places you can remove them but it is not easy.  Try to remove them from structures by slipping tweezers or a similar small tool between the cocoon and the wall. Wear a long-sleeved shirt while doing this job.  The hairy caterpillars can shed irritating hairs. A good pressure washing after caterpillar season goes a long way towards freeing your house of the cocoons.

In the long run, these caterpillars are unpleasant but not a huge problem. With patience, this “plague” will be over soon and you can enjoy your piece of paradise once more.

 In Florida, we have three species of tussock moths (Orgyia species).  Orgyia detrita. Caterpillars have a dark body and a red head, with 2 black tufts of hair projecting forward like antennae, there are dense tufts of hair on their backs, and a fluffy tuft in the back which resembles a tail. Unique to this species are the orange-colored spots along the back and sides. Caterpillars of the white marked tussock moth, Orgyia leucostigma, are similar looking but are distinguished by their lighter body color and yellow spots. The rarely-encountered third species, Orgyia definita, has a yellow or tan head to go with its pale body, hair pencils and tussocks.

Photographs by the University of Florida/IFAS Department of Entomology & Nematology

Jim Moll, UF/IFAS Pasco Extension Florida-Friendly Landscaping Program Coordinator (March 22, 2017) and Whitney Elmore, UF/IFAS Pasco Extension Director/Urban Horticulture Agent

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