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Golden sunshine and a bluebird sky arched above as we meandered down a lonely backroad. I was paying attention to driving, but my passenger was focused on something else. “Apples!” he exclaimed suddenly, as we cruised past a few trees in the road ditch. He’s always on the lookout for apples. We turned around and pulled off the shoulder, then rummaged around in the car for bags. Soon we were clambering down the bank.
The first tree we came to had small, yellow apples. One bite was all I needed. The tart, dry flesh was impossible to swallow. We moved on to the next tree. Plucking a deep red apple, I discovered that it had a large brown spot on the far side. A tentative bite revealed mushy, sweet innards. “Might be good for sauce,” I mused. Every fruit we picked had a brown bruise, though.
Looking back toward the first tree I noticed a third trunk, its branches so intertwined the others that we hadn’t noticed it at first. The large, yellow-green apples were burnished with red, and they dangled invitingly among deep green leaves. One bite was all I needed. Crisp flesh fairly jumped through my teeth, and a tart zing added interest to the sweetness. Now this was an apple. We quickly filled our bags.
Arriving home, we discovered the driveway full of an entirely different type of apple. Small, brown, dried-out spheres lay among the fallen oak leaves. If you could make ping pong balls out of brown paper bags, this is what you’d get. Not very appetizing, but then that’s not their goal, and their purpose has already been fulfilled.
Oak apples are not a fruit at all. They are galls – the nurseries for tiny wasp larvae. Earlier this summer, a woman pulled a similar gall out of her pocket so I could identify the outbreak at her home. The color drained from her face when I mentioned wasps, and I could see through her panicked expression that she was imagining a swarm of yellow jackets ambushing her yard. Luckily, the wasps that create these galls are the small, non-stinging kind, and she has nothing to worry about.
While oak apples won’t make good applesauce, they do provide food for thought. Oak apple gall wasps (there are several different species) have a complicated, double life cycle, known as the “alternation of generations.”
The brown, papery galls now on my driveway once protected growing and pupating wasp larvae high in the branches of an oak tree. Male and female adult wasps exited the galls this summer. The wasps mated, and then the females burrowed into the ground where they laid their eggs on the roots of oak trees. The larvae from those eggs will feed on the roots of the oaks for more than a year before they pupate. They emerge as generation of female-only, wingless wasps. This underground segment of the life cycle, from egg to larvae to pupa to wingless female adult, takes over a year. The offspring of the galls I found this fall won’t surface until May of 2017.
As the ground warms in spring, the wingless females will emerge and crawl up a nearby oak tree. In this asexual generation there is no need to mate. The females will inject eggs into expanding leaf buds. The small, round, larvae of the next generation include both males and females who chew into the leaf stems. Chemicals in their saliva stimulate the leaf tissue to swell. The galls continue to expand as the leaves and larvae grow, providing both food and shelter to the developing wasp.
These larvae pupate in late summer, and emerge as small, dark, male and female wasps to begin the cycle again. Once empty, the galls drop to the ground and dry out.
Just like the true apples we picked along the road, galls come in a diversity of colors and textures. There are over 50 species of wasps that produce oak apple galls in North America, and each wasp’s gall is slightly different. Most fall into two general groups – galls that have an airy web of fibers radiating from the central larval capsule, and galls that have juicy, spongy, fruit-like tissue. All galls made by Cynipid wasps would taste terrible, though, since they concentrate bitter tannic acid from the oak as a defense against fungi and bacteria.
The tart zing in my apples will also keep bacteria at bay – and taste great – once I preserve them as sauce. Oh autumn, you are the apple of my eye!
For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI! Our new exhibit: “Lake Alive!” opened May 1, 2015, and will remain open until March 2016.
Find us on the web at www.cablemuseum.org to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot, http://cablemuseumnaturalconnections.blogspot.com.