Slugs at Lake of the Clouds

2016 June 1

We took a day trip down to the Porcupine Mountains[1] to see the Lake of the Clouds on June 14, 2015, just to see what we could see. This is the view from the cliffs overlooking the lake, a few hundred feet up.


As you can see, it is a bit on the cool and moist side. This is a pretty typical climate for the region. Which means that if you take the trail from the lookout down into the woods, it is practically a rainforest down there.

And where there is moist vegetation, there are usually slugs.


These are the kind of slug we usually see around here – a bit over an inch long, and kind of wrinkled.


I understand that their “eyes” aren’t actually very good at imaging, they are more just light detectors.


I am not entirely sure whether there are any land slugs that are native to Michigan, all the references I find to Michigan slugs only mention non-native species. Probably because unless a slug is a pest, nobody much wants to know about them, and non-native species of anything seem to be more likely to be pests than native species. These look kind of like Dusky Slugs, Arion subfuscus, which are supposed to be well-established in woodlands throughout Michigan even though they originally came from Europe.

We also found this snail.


A likely ID is the Eastern Forest Snail, Anguispira alternata, which evidently is a native species. These are pretty common in moist forests. They are also one of the hosts for brainworm, a deer parasite. The snails eat deer droppings that contain brainworm larvae. These then develop inside of the snail, until eventually the snail gets accidentally eaten along with a mouthful of leaves by a deer. The brainworms then migrate inside of the deer’s body, and mature in the membranes surrounding the brain. The mature brainworms then lay eggs that migrate to the deer’s lungs, where they hatch and are coughed up and swallowed. From there, the larvae are carried out into the deer droppings, and the circle of life is complete. The white-tailed deer that we have around here tolerate these parasites fairly well, but if a moose gets infected then the brainworms penetrate too deeply in the brain. The moose gets weak, lame, disoriented, partially or completely blind, and loses fear of humans to the point where they are likely to wander into towns. If the infection is severe, it is likely to be fatal.

I don’t think brainworms can infect humans, but just in case – don’t eat raw snails that you find in the woods.

[1] Yeah, yeah, I know. All you people who live out west or someplace like that are saying, “You call those mountains? Those are just hills!” Well, they’re what we’ve got. But at least our mountains are old. They were uplifted as part of the Penokean orogeny about 1.8 billion years ago, with some significant extra lava flows and uplifts during the formation of the Midcontinent Rift System 1.1 billion years ago, and have been wearing down ever since. As opposed to, say, the Rocky Mountains, which were mostly uplifted in the period from 80 million – 55 million years ago, and haven’t had nearly as much time to erode away. Or the Himalayas, which are still being uplifted now, and are growing at a rate of about 5 mm/year.

2 Responses
  1. Carole permalink
    June 1, 2016

    Life cycles can be amazing. Florida is only 53 million years old.

  2. July 6, 2016

    Carole: Yep, the geologic history of Florida is very, very different from that of Michigan

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