Walking around the garden after this afternoon’s light rain I noticed that one of the small weeping Golden Chain trees (Laburnum x watereri ‘Pendulum) was mostly defoliated. Heat? Drought? No, I looked closer to find a few handfuls of caterpillars (White-marked tussock moth caterpillar, below) actively munching on the few remaining leaves. I supposed that the white protrusions on the backs of the caterpillars were wasp larvae like I’ve seen on hornworms, but a bit of research by my wife revealed that these are tufts of white hair.
Nevertheless, a solitary wasp was on the prowl, moving the length of each branch (looking for caterpillars, I suppose). I lingered for quite awhile to see what would happen, until the agitated wasp gave me enough dirty looks that I figured I’d best retreat. After a few minutes I returned with a twig to dislodge the caterpillars, and hopefully save the last few leaves. I dared not swat them away by hand. I noticed that the caterpillars had antenna-like protrusions and spines, and in the past I’ve brushed against these to receive a mildly paralyzing sting.
I noticed a second group of four hairy, red caterpillars on the tree, but these were not actively eating leaves at the moment. They were flicked off onto the ground below as well, and I’ll check tomorrow to see if they have made their way back into the tree. In the middle of August I’m not too concerned that the tree will be weakened by the loss of foliage, but I thought it best to avoid losing every leaf.
Along the wooded edge of the garden several small red mulberries are currently infested by fall webworms. In a similar manner these caterpillars have stripped the trees nearly bare, but the mulberries are a bit of a nuisance that I must regularly prune to keep them out of nearby magnolia and dogwood. I occasionally consider taking a few minutes to chopping them out, but there’s always something to be done that involves less labor, so there they stand. It wouldn’t hurt my heart if the caterpillars were to kill the mulberries, but I doubt it will come to that, and the caterpillars are unlikely to spread to the other trees. Both the mulberry and Golden Chain trees will probably have stored enough reserves to survive until spring without foliage.
I don’t think there’s much of a lesson to be learned from this experience. I’ve not sprayed pesticides for bugs of any sort in years, and caterpillars are easily controlled if they are observed early on. I’ve walked past the Golden Chain tree dozens of times over the past week or two when the caterpillars would have begun chowing down, so the blame here is on my lack of attention. With a small number of caterpillars they can be hand picked (or flicked to ground with a stick if you’re afraid of them like I am), and tent caterpillars and webworms can be dislodged with a stick or with a spray of water. The damage they inflict is usually not fatal, in particular when the damage is done at the tail end of the season.