With a firmly packed trail under my feet, I could let my eyes wander. Blue sky peeked through gaps in the red pine canopy, and the orderly rows of their trunks made pleasing patterns against the snow.
On this hike, though, I wasn’t looking for uniform trees. This was a scouting trip for an upcoming interpretive hike, and my eyes were peeled for special or unusual bits of nature that would make participants go “wow!”
Through a brushy patch I noted a young boxelder tree with winged samaras still drooping from the twigs. Across the trail, a cherry sapling sported the wrinkled growths of black knot fungus, and the leaves of a young oak tree fluttered in the wind.
This could be a stop where I talk about easily visible clues to winter tree identification, I thought.
A few steps down the trail, another oak sapling caught my eye. This one was only chest high and barely half-an-inch in diameter where it disappeared into the snow. And it was hairy.
My second look revealed that the twigs were covered with small, shiny, brown domes, and from most of these domes sprouted a forest of little black clubs. Their shape reminded me of Earth tongue fungi and pin lichens, both of which I’ve written about previously. As I finished hiking the loop, I spotted these odd-looking twigs everywhere.
The domes I recognized. Several years ago I spotted the same type of critter on an ironwood tree. These were scale insects. Like their relatives the aphids, scale larvae insert sucking mouthparts (called stylets) into the leaves and start drinking.
In order to get enough nitrogen, they must drink an excessive amount of the sugar-rich sap, which they concentrate and excrete as “honeydew.” Ants take advantage of this just like they do with aphids, and can often be seen drinking honeydew off the scale insects.
As the nitrogen and sugar fuel their growth, the scale larvae molt. With each molt, their bodies become larger, and their legs become smaller. Finally, in late summer before their legs completely disappear, the nymphs walk back down the leaf stalk and onto their winter home on the twig. They build their waxy, protective shells, and do not move again. Spring brings maturity, egg laying and death.
Death, in this case, came early. I sent a photo of the scale insects with clubs erupting from their shells to Britt Bunyard. Britt is the editor of Fungi Magazine and a frequent field trip leader for the museum. I affectionately refer to him as “my mushroom guy” and send most fungi-related questions his way. He studied entomology as well, so this mystery was perfect for him.
Britt wrote back that these fungi were most likely cordyceps clavulata. Cordyceps fungi are well known to plant pathologists and agronomists because, according to Britt, “they are one of the rock stars of biocontrol of insect pests on economically important crops.”
In other words, these fungi are on our side and help control pests.
Cordyceps are fungi who parasitize insects (mostly). First, a spore encounters a tasty host, then it sends web-like mycelium throughout the body of the insect to digest it. Finally they send their club-like reproductive structure up into the air to release spores. The cycle repeats.
According to Britt, there is only one known reference to cordyceps fungi parasitizing scale insects. This could be a unique observation and important to science! I have marching orders to collect samples for further research.
You may be familiar with cordyceps, because HBO’s recent zombie thriller “The Last of Us” is purportedly about cordyceps that switch from attacking insects to attacking humans. I’m not sure because I haven’t seen it. I don’t watch the horror and apocalypse genre, especially when it’s based in nature.
For one, I do not want to be thinking about that stuff while I’m in the woods. For two, real nature has plenty of suspense and gore if you know where to look. Luckily these real-life fungi are the good guys. They’ve just taken care of what looks like a huge outbreak of scale insects in this section of forest.
As I searched for more details, I discovered that oak lecanium scale insects become pests most often in cities. Sometimes it’s because the heat island effect in cities both stresses out the trees and allows the scale insects to develop faster.
Sometimes it’s because spraying for mosquitoes has killed off the predators and parasites who would control the scale insects. I called around to nearby landowners, and no one admits to having sprayed for mosquitoes in this forest. My friend who hikes there in the summer confirms that there are plenty of skeeters on these trails. So the cause of the outbreak remains a bit of a mystery.
Happily, mysteries are fun to teach about. Not only did I find something interesting to show the visitors next week, I discovered something that made even my mushroom guy go “wow!” Now that’s a successful hike.
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