Tuliptrees, covered in scales

Tar Hollow State Forest, June 16, 2012. I was down there in the company of Kelly Williams-Sieg and Brian Zwiebel doing a bit of off-road bushwhacking in search of warblers. As a side benefit (?), I got to experience firsthand a phenomenon that I had been hearing about from Kelly, Bob Placier, and others in southeast Ohio.

In Tar Hollow, and just about every other forest in Ohio's hill country, there are plenty of tuliptrees, Liriodendron tulipifera, a large and stately member of the magnolia family.

NOTE: Not "tulip poplar" or "yellow poplar", which are oft-used misnomers for this plant, especially in forestry circles. It's a magnolia - a distant relative of the Salicaceae family, which includes real poplars such as cottonwoods, aspen, poplars and willows.

Now that the nomenclatural theatrics are over, back to the tuliptree, which is the main protagonist of this story. For weeks now, I've been hearing stories about sticky sap raining down from the forest canopy, and more than a few people have been flummoxed as to its origin. So prolific are these viscous secretions that woodland explorers would return coated in with the substance, as if sprayed by a giant mace can full of maple syrup. The gluey stuff provides a nice veneer to which dust, plant bits, and about anything else small enough to drift about can stick fast. Hikers would return from journeys looking like Pigpen.

The upper surface of a common greenbrier, Smilax rotundifolia, glistens with sticky honeydew. Just about all the leaves in the forest looked this way, and by the time I left the woods, so did the top of my head. Running a comb through my hair was akin to dragging a cloth down a strip of velcro; a shower was the only solution for de-sapping.

Bob Placier first tipped me to the cause of the arboreal glue, and shortly after that Dennis Profant posted one of his typically informative essays about this phenomenon on his excellent blog.

The cause of the sticky rain is an odd insect known as the tuliptree scale, Toumeyella liriodendri. The branch in the photo is liberally shingled with the insects, and honeydrew droplets are beading up as if a fresh rain just passed through. When one considers that just about all of the tuliptree twigs are scaled in this manner, it's small wonder that sticky liquid is pelting everything below. As the scales feed on tuliptree sap, they excrete the lovely honeydew that coats everything in the forest. Park your car under some infested tuliptrees for a while, then motor off down some unpaved dusty roads. You'll be heading to a carwash before long.

Tuliptree scales resemble barnacles more than insects, and if one were unfamiliar with them it'd be hard to figure out what they were. Once a female scale insect finds a suitable attachment point, she inserts her piercing mouthpart into the plant tissue, and begins to uptake sap. As the scale grows and matures it secretes a waxy covering, and apparently reabsorbs its own legs and eyes. I don't believe male tuliptree scales feed in this manner; they exist primarily to mate with females. But female scales can do without males, too, it seems - they are capable of parthenogenetic reproduction, or essentially cloning themselves. If you want a more in-depth look at these interesting bugs, check Dennis Profant's blog posts, HERE and HERE.

I haven't heard a good explanation for this year's massive outbreak of tuliptree scale, although the scale of this year's scales is beyond what anyone I know can recall. Perhaps unseasonably warm winter and early spring weather helped them to survive in greater than normal numbers.

There are always exploiters, and in the case of tuliptree scales the winners are certain ants, beetle larvae, wasps, and perhaps other insects that either feed directly on the scales, sip the sweet honeydew, or prey on the aforementioned. If you are a human, and spend a lot of time in forests dense with tuliptrees, you probably will not consider yourself a beneficiary of tuliptree scales.