Wednesday, July 25, 2007

A Glimpse of the Black Walnut Canopy

Black Walnut inflorescence

Canopy trees conduct most of their business out of our sight. Upward-facing leaves photosynthesize, flowers exchange pollen via wind or winged pollinators, and only a fraction of their fruits and seeds fall to the ground where we can see them. That's why trees like these black walnuts on the forest-edge are a special treat--they are open for business near ground-level.

Besides this glimpse of floral morphology, these black walnut trees (relative youngsters, with trunk diameters under 12 inches) have been displaying their canopy fauna for me. The most spectacular insects feeding on walnut are the saturniid moths. My Luna Moth and Imperial Moth both fed on walnut leaves as caterpillars, and I suspect this sphinx moth is from a walnut-feeding species as well.

The assassin bug (Zelus sp.) is a predator, not host-plant specific, but usually found on shrubs and trees with sunny exposures. With a busy assemblage of hemipterans, caterpillars, and flies, these walnuts provide a rich hunting ground.

In contrast, the spittlebugs and the membracids I've followed are probably host-plant specific to walnuts and their relatives. (There were also several tiny mirid species too small and quick to photograph, and I know some of these are host-plant specialists.) Walnut sap is rich in aromatic compounds and special enzymes allow sap-feeding specialists to detoxify their food.

The hemipteran insects I've been photographing completed their life cycles early in the season and disappeared by the first week in July. At this point, I'm only seeing generalists like Japanese beetle working the leaves. I'm still watching, though. There are some interesting gall-like growths on the lowest walnut branches, and I expect I will have more surprises before winter. Perhaps, if the walnut fruits don't abort, squirrels and bears will visit. A few years ago, a bear woke us at dawn with loud crunching. He was stretched out on the porch, chewing up my hulled walnuts, sucking out the meat, and spitting out the shells in a tidy little pile next to the walnut bag. Anyone who has cracked black walnuts can marvel at his strength of tooth and jaw.


Dave said...

We have a lot of walnut trees. I'm going to have to start looking for some of these things. I didn't know bears ate the undeveloped nuts!

OfTroy said...

My that is a strong jaw.

Joy of Cooking suggest putting walnut into a gunny sack and driving the pick up truck over the sack a few times to crack the hulls..
(funny to me, who grew up in NYC, didn't have a driveway till i was married, and never have owned a pick up truck (compacts!--parking is at a premium.. small cars fit into small spaces!)

Rebecca Clayton said...

Dave, tastes differ in bears as well as people. Our bear wasn't eating undeveloped nuts, though. He was eating walnuts I'd hulled but not yet shelled. I understand you can pickle green walnuts, but I'm not sure if that would work for black walnuts or not.

Helen, (That's how I think of you, although maybe "oftroy" means something completely different--if so I apologize.) I hulled these walnuts with a minivan--I suspect a small car would work well enough. Black walnut shells (which are inside the sticky, brown-staining hulls) are so tough that they usually don't crack even from a car driving over them. I use a hammer.