An abundance of morning fog & tenting caterpillars
- John Lorson: The Rail Trail Naturalist
- August 21, 2020
- 1179
For as long as I can remember, I’ve marked each foggy morning in August with a smile and a prediction: This means another snowfall come winter.
I’m quite certain the folklore prognostication was handed down to me by my mother, who grew up on the farm at the knee of an old dairy farmer. Before Doppler radar and 24-hour-a-day weather alerts, folks had legend, lore and a very keen sense of their surroundings. Mom could feel rain coming two days away and could call it to the minute by looking at the leaves on the trees.
There’s a lot to be said about folklore and weather predictions, and some of it is probably even true. As for the number of August fogs and their correlation to winter snows, I’ve never actually tabulated the accuracy of the statement, but that doesn’t keep me from having some fun with it.
So far this August I’ve seen only a handful of foggy mornings. Fog typically forms when cool, clear nights follow warm, humid days. Overnight, the earth radiates heat into space and cools at the surface. Heavy, moisture-soaked air crowds the valleys, and cool air rolls down the hillsides to gather in those same lowlands, driving the thermometer down to the “dew point” — the temperature at which the air is fully saturated and water vapor condenses into tiny water droplets. The result is essentially a cloud trapped so close to the ground that we’re walking, riding and driving through it.
It should go without saying that traffic, no matter the conveyance, needs to slow down appropriately in the fog and use caution both on the roadways and on the trails. Folks traveling the trail often presume that because they are simply walking or riding along at a relatively slow speed, they’ll have plenty of time to react if another traveler approaches through the fog. That’s not necessarily so.
If you are riding your bicycle at 20 mph and I am riding toward you through the fog at the same rate, we are closing in on each other at nearly 60 feet per second. That’s not a lot of time or distance to steer clear of disaster. It’s always best to be as lit up and visible as possible, especially on those foggy mornings. A flashing white strobe light (like those on top of a school bus) can go a long way toward cutting through the murk to show someone you’re there.
While fog can limit visibility of distant objects and even make close and familiar shapes appear a bit foggy, some things are actually accentuated by the fog. Take for example the work of the fall webworm, the tent homes of which seem to collect the fog and “glow” like ghost arms reaching out from the trees.
The lesser evil of two common caterpillars that are sometimes mistaken for each other, the fall webworm often gets a worse rap than it might deserve because of the damage done by its cousin, the eastern tent caterpillar. The latter is a spring-active caterpillar that spins its “tent” home in the crotch of a budding tree. During the day the caterpillars venture forth to eat young foliage before it ever has a chance to benefit the tree. In the evening they retreat to the safety of the tent. The location of the nests can thwart tree growth and cause death to individual branches.
The fall webworm, while admittedly unsightly, is often less damaging to its host because it reaches its most active state later in the season (July and August) after a good bit of photosynthesis has already taken place in the leaves it consumes. Also, the fall webworm typically nests near the ends of branches, devouring this season’s foliage but leaving the branch intact and, hopefully, ready to bud again come spring.
Both eastern tent caterpillars and fall webworms have a broad range of natural predators. Each becomes quite vulnerable as they spend time on the ground to pupate, and when they take to the air as moths — the eastern tent moth a rather nondescript brown moth and the fall webworm moth a striking, nearly all white edition — both become a valuable food source to a whole host of other creatures as they mature, are an important component in the food web, and are nowhere near as destructive as the non-native gypsy moth and other such invaders.
If you have comments on this column or questions about the natural world, write The Rail Trail Naturalist, P.O. Box 170, Fredericksburg, OH 44627, or email jlorson@alonovus.com.