Somebody laid eggs on my bur oak branch

I’m tracking the passage of the seasons by following a branch on a stately old bur oak at the University of Minnesota.

The season hasn’t changed, of course. It’s still summer, and, in fact, the temperature in my neighborhood probably jumped last week with all the students wandering around looking for classes and waiting for buses.

But the start of school feels like fall, a correlation that’s hard-wired into most of us, so I went over to the tree last week to take a look.

The campus may have been sleepy this summer, but my branch looked as though it had seen plenty of activity. Here’s how it looked a few months ago on the solstice:

The picture of arboreal innocence and optimism — velvety leaves, fuzzy new branch growth. But last week there were holes in the leaves and a mysterious black knob.

For help with interpreting what I saw, I sent my photos to Jana Albers with the Minnesota Department of Natural Resources. She said that my photos showed evidence of eating and egg-laying.

First the eating.

Picky eaters just go for the green part

Beetles, the kind that prefer green cells, not the tough leaf-vein cells, probably nibbled on this leaf, she said, and left behind the lacy holes.

Somebody else, a less discriminating eater, chewed a jagged hole in another leaf.

Wholesale munching here

It was probably a forest tent caterpillar. No delicate nibbling with forest tent caterpillars. They gobble everything — tender green cells and the tougher vein cells. Forest tent caterpillars are native to Minnesota, and this oak tree certainly isn’t being eaten to death by them. Still, it was a little disconcerting to discover evidence of them.

On to the egg laying.

A moth apparently took advantage of my oak branch to start the procreation process.

See if you can count the eggs!

The dark round object surrounding the branch is an egg mass, probably deposited (laid?) by some kind of moth. Albers said she couldn’t tell which kind of moth, but she suggested I look for fifty to one hundred tiny caterpillars emerging next spring.

This was starting to feel like Charlotte’s Web.

My branch has no acorns on it, but other branches on the tree undoubtedly do because the tree is starting to drop them. Bur oaks drop their seeds between August and November. Some of the oaks nearby had dropped a lot, but there were only a few beneath my tree. On this day, they cast long shadows across the sidewalk in the late afternoon sun.

Bur oak acorns hide inside a bristly fringed cap

The university is no longer sleepy. Standing near my tree in front of Eddy Hall, I saw quite a few of those students doing the fall thing — wandering around, waiting for buses. I also watched a young man (black car, lower left in the photo below) spend nearly an hour at the intersection. The engine was idling, but he was busy. Texting. Hope he didn’t miss any classes.






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