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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.


Brent C. Kryda said…
It's funny how this tree gets regarded in such strong ways depending on where you happen to find yourself. In Ontario it is considered a "southern tree" and regarded with awe for its amazing potential height and girth, even with the Eastern White Pines we have putting them to shame. In much of the eastern U.S. it seems to be recognized as a lovely tree, but not something worth the praise that it gets in Ontario. In Florida, it is considered a "northern tree", one of many insignificant species that persist this far south, and in some circles is even a nuisance for robbing space and soil from Florida's "true natives". In any case, it is well-known enough to have made it a landscape choice of George Washington who planted the trees which still stand along the front lawn space of Mt. Vernon.
Jim McCormac said…
Good stuff, Brent. I'm with George W. - I think tuliptree is one of the best trees in the eastern forest. Stately, towering and columnar, with exquisite flowers, and playing host to tiger swallowtails, tuliptree beauty moths, and many other cool insects.
terskac said…
My neighborhood trees were covered with a white scale insect a decade or so ago. I think they were on both maples and pin oaks but it has been so long I don't recall exactly. It was a real infestation but they have not returned. They caused a lot of worry among the homeowners at the time. These also emitted sticky goo on everything. They looked like tiny cotton tufts
Carole said…
Do the scales harm the trees?
Brent C. Kryda said…
If you ever get the chance, explore Rondeau Provincial Park and the surrounding areas on the other shore of Lake Erie. There are some towering Tulipiferae there that also grow in rather swampy soil, creating something of a Bald Cypress swamp effect during the spring.
Jim McCormac said…
Thanks for your comments everyone, and Carol, I don't think the scales do lasting damage - just create a short term mess.
zippiknits said…
We had a couple of beautiful tuliptree specimens growing on a slope behind a local historical building. Then the slope gave way, taking the trees with them.

They were beautiful trees, very large, and I still miss them. Scale we have, too, usually all over my citrus trees. I wash them down with soapy water because they harm the trees since our garden citrus trees are dwarves.

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