Controlling Caterpillar Pests with Duct Tape

I was coming in from the laundry room well before sunrise one June morning and in what little light there was, I saw something moving down a mesquite tree that shades the patio. It was a squirming army of caterpillars of some sort, moving down the trunk as fast as they could wiggle.

The caterpillar infestation explained the tree's failure to thrive that spring - the bean crop was vanishing, and unlike the other mesquites, it had not put out many new shoots. It wasn't dying, just not thriving, and had never recovered from the usual ratty winter mesquite look. A co-worker and I discussed the easiest way to get the pests under control and came up with a brilliant idea.

The brilliant plan:
* Let the worms get up in the tree from their daytime hiding place in the pebbles mulch.
* Band the trunk with an adhesive material late that night.
* Worms would get stuck on the adhesive on their way down at dawn.
* Mockingbirds would arrive at daylight and eat the worms for breakfast.
* The tree would be saved.

What actually happened with the brilliant plan:
* The worms went up the tree.
* I banded the trunk with duct tape, wrapped sticky side out in about a 6-inch band.
* The herd of worms trying to descend the tree at dawn was so big that they were pushing each other off the trunk, many of them never reaching the adhesive. Others reached the tape, were repelled by the sticky feel of it, went back up the tree and hurled themselves off the trunk or branches in desperation as dawn approached. It was raining caterpillars.
* When daylight arrived, birds started to dine on the dozen or so worms that did get stuck on the tape.
* My cat discovered the buffet. He sat in the tree, above the tempting wiggly worms, waiting for the birds to get close enough to catch.
* Not only was the tree not saved, a few birds became catfood.

After some more discussions, we designed a worm trap. I placed a 5-gallon bucket at the base of the tree with a stick leading from the tree trunk above the tape into the bucket. A couple of broken flowerpots in the bottom of the bucket gave the worms something to hide under. The first night's collection was sparse, maybe a dozen or so worms. The second night's collection was huge ... a hundred or more worms. Apparently they follow scent trails and the few worms of the first night created a path that led the next night's collection to their doom.

I dumped the collection into a shallow plastic dish and set it on the gate pillar for the birds, away from any cover the cat could use for ambush. Four mockingbirds, a herd of sparrows, and a couple of tiny wrens quickly cleared the buffet. The third night I collected fewer than a dozen worms.

Results - new shoots! Within a couple of weeks I had new leaves coming out, and new shoots on the end of almost every twig. The density of the shade under the tree is almost twice what it was.

The Easiest Control Method So Far

A few days later I taped another mesquite tree that is within a few feet of the infested one, but did it in the afternoon because I wanted to see how many worms were trying to go up the tree that evening. When I checked the tree late that night, although there were worms trying to climb the trunk, large red ants (a species I have never seen in the daylight) were swarming the trunk and hauling the worms away. It doesn't seem to matter whether I prevent them from climbing up or down, they have predators that will get them.

A repeat of the taping over the 4th of July weekend showed a few small worms - those that hatched after the first trap. I had to tape the trees about once a month that summer to keep the worms from regaining a foothold.

The Alternatives

When I posted this method on a newsgroup, a couple of people suggested spraying with Bacillus thuringiensis to kill the worms. Yes, it would work, but it's expensive (especially compared to duct tape) and not nearly as easy to do. I don't want to scramble around in the top of a spiny mesquite with spray equipment if wrapping a few feet of tape around the trunk will accomplish the same thing.

The one caution with the duct tape caterpillar control: don't leave the tape on more than a few days a month. It traps moisture and you can damage the tree's bark.