When is a Caterpillar not a caterpillar?
When it’s a Deere.
No, no, that’s not it. What I meant to say is:
When it’s a Sawfly.
Which doesn’t mean it’s a fly … although it might carry a saw. Sawflies are actually more closely related to wasps and bees than flies, and some females use a saw-like appendage to cut into plant stems to lay eggs. The larvae then emerge en masse to strip the plant of its leaves. In wasps the saw/egg-laying apparatus sometimes doubles as a stinger. Not so with sawflies.
Pine sawflies lay their eggs on pine trees, and spruce sawflies on—you guessed it. If you have ever grown mugo pine, you’ve probably seen branches populated by writhing black-headed larvae of European pine sawflies. At first look at the twitching needles it appears that the branches have become living, moving creatures. Get too close and they rear up in unison, Wizard-of-Oz like. (What’d'ya think you’re doing?” cried the apple tree when Dorothy plucked an apple.) You run to fetch some poison, but by the time you make it back to the scene, the pine looks like a badly clipped poodle.
The beady black heads on the “caterpillars” that were busy skeletonizing my hibiscus leaves led me to suspect that they were not really caterpillars. I admit to first spraying them with Bt (a caterpillar killer), to no avail. Bacillus thuringiensis has zero effect on larvae of the Hymenoptera order—a good thing for bees, in this world of Bt modified crops. But I digress. When I came back an hour later to find the little wormies still munching merrily away I did what I do so well. I googled “caterpillars on hibiscus.” Sure enough, up came an image of the culprit.
Yes, they were hibiscus sawfly larvae. Making lace of my beautiful ‘Summer Storm.’ And the little “flies” hanging around the scene were the adults. They have the same black beady heads as the larvae, but the sure identifier is the red-orange smudge just below the heads. Somewhere, hidden on the body, is a sharp egg-laying instrument. At first, the larvae will be visible on the older leaves of your hibiscus. That’s because the eggs take a week or so to hatch. The plant grows so quickly that the new leaves emerge before the larvae are even detectable. They’ll get to the tender stuff soon, you can be sure. I got out my neem/soap spray, which did the job, until the next round of eggs hatched. Repeat, repeat, and repeat again.
Did you know that there are more than three dozen species of conifer-eating sawflies alone in North America? And then there are 700 more species known as the common sawflies. Currant sawflies feed on currants, willow sawflies on willow, and so on with azaleas and ashes, columbines and birches. Every plant, it seems, has its sawfly. Rodents eat the pupae, and some birds—titmice, for example—will eat the larvae, which is why the entire forest has not been reduced to leaf veins. The larvae, in turn, have come up with some sneaky avoidance maneuvers, such as the scary pine branch twitching motion.
This brings me to my next sawfly sighting of the summer.
Dogwood sawfly larvae cleverly disguise themselves as bird droppings by exuding a white waxy substance and curling up into circles. What self-respecting bird would consume its own poop? But place one on your hand and it, apparently, immediately knows that the jig is up. It drops its coat and becomes the color of a leaf—which is not much of a camouflage on a hand, but the wonders of nature have their limits.
Another fascinating member of the sawfly clan is the butternut woolyworm, which looks, at one stage in its life, like a mass of wooly aphids—although why it would take on this disguise is a mystery. You can be sure that I will be looking for this bizarre creature with a penchant for the undersides of Juglans (walnut and hickory) leaves.
And all the rest of the hungry leaf-eating hymenoptera.