Monthly Archives: August 2012

Unusual mating behavior alerts us to an invasion of giant slugs

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A pleasant outdoor evening for Cari and Jason Reynolds was interrupted by the antics of some rather large slugs. The slugs had entwined their bodies, then suspended themselves from a stiff strand of mucus. Two large translucent structures emerged from their heads and coiled together. Sex, slug style. More precisely, sex, European slug style; American slugs have more pedestrian ways of completing their unions. For readers with sluggy, salacious turn of mind, the Ever So Strange Animal Almanac has a description (note for the bemused: some British slang involved) and David Attenborough narrates the whole process with some “marvels of nature” music playing along. Bottom line: the translucent structures were penises, exchanging sperm between two hermaphrodites.

Cari alerted the world through Facebook and I requested a closer look at these creatures. Thanks to a prompt delivery by Jason, I’m now in possession of two specimens of Limax maximus (well named, they grow to eight inches long; photos below). These are the first that I have encountered on the Cumberland Plateau. This worries me a bit, not just because the spotless innocents of Sewanee and surrounding areas are perhaps not ready for regular exposure to giant penis-dangling hermaphrodites, but because these monster slugs may be about to invade our woodlands and out-compete native species. We’re in one of the world’s epicenters of gastropod diversity, so such an invasion would be one more loss in the ongoing worldwide (and local) erosion of biological diversity. In the northeastern U. S., non-native slugs have thoroughly disrupted the local ecology. We have far more native species, so the damage here would be that much more troubling.

The species has been present in the cities of the Northeast since at least the late nineteenth century. Tyron’s Manual of Conchology published in 1885 includes a plate featuring Limax maximus (top two animals in the plate). In these more northerly areas, the slug seems to prefer to live in disturbed habitats and gardens, so it might not invade the forests here. However, our climate is more slug-friendly that that of Boston and Philadelphia; we can’t assume that the species will behave in the same way here as it does elsewhere. Stay tuned for further adventures in the biology of invasive species. Up next: Arion, an exotic slug that is ubiquitous further east, but has not yet been seen in Sewanee (to my knowledge — keep the reports coming!).

Limax maximus. Junebug for scale.

One common name is “leopard slug.”

Five inches. Three more to go. They can live for several years.

“There sleeps Titania sometime of the night, / Lull’d in these flowers”

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Now that late summer is upon us, bumblebee nests are full of worker bees. These bumble-workers often stay out in the field at night, sleeping in flowers. I found this bee in a dewy Yellow Cosmos bloom. She was completely still, paralyzed by the cool morning temperatures.

Like mammals and birds, bumblebees are endothermic, meaning that they warm themselves from internal heat sources. Bumblebees do this by shivering their flight muscles as they wake in the morning. Until they reach running temperature, they are sluggish and can barely move a leg, let alone fly.

In the arctic, some bumblebees use their bodies’ heat to incubate eggs and young bees, just like a mother bird. Without a boost of maternal muscle-heat, the bees would not have enough time to complete their life cycle during the short arctic summer. This endothermic physiology explains why bumblebees, especially northern bumblebees, are furry: like birds (feathers) and mammals (hair), they have a layer of insulation to retain hard-won heat.

Our local bees’ nightly cold stupor saves energy. But immobility is is a dangerous habit, especially for footloose bees who like to sleep outside of the nest in exposed flowers. Yesterday, I watched a European hornet patrolling the profuse blossoms on a clematis vine. Every time it came across a bee or fly, the hornet lunged, trying to grab the victim.

Look sharp, little bee. An evil Puck is after your life.

Saddleback caterpillar, Acharia stimulea

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The pain receptors on Marianne Tyndall’s arm found this impressively spiny caterpillar on some garden vegetation yesterday. The caterpillar is about two inches long. Its sting causes pain that feels like a combination of burning skin and tearing muscle. Pretty impressive. The pain is bad enough to cause some people to call a poison center, as reported here. Note that the paper in this link uses the old genus name, Sibine. The paper also relates events in Louisiana where people evidently have different attitudes to caterpillar attacks — in Sewanee, we suck up the pain, then carefully gather the caterpillar to bring it to fellow naturalists.

The stinging hairs deter predatory wasps and assassin bugs. Wasps learn to recognize the caterpillars and after a few inspections, leave them well alone.

The colorful caterpillar turns into a fuzzy brown moth.

Ringneck snake

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I found this ringneck snake (Diadophis punctatus) under a piece of firewood from the pile in our driveway. The snake either came as a free bonus with the wood or it colonized the new hiding place in the last couple of days. Either way, the wood is stacked, so the snake is roaming the garden. It is probably joining many others of its kind. This species can, in the right conditions, live at very high densities (hundreds per acre).

I held the snake for just a minute or two, and in that time it demonstrated its two favorite methods of defense. First it writhed around, flashing its bright underbelly at me, then it oozed nasty-smelling saliva from its mouth. Despite a thorough scrubbing, my hands still smell musky. If severely provoked, the snake will bite, but I merely handled it for a photo, then released it, stopping well short of this level of torment. The bite is not dangerous to humans.

Ringnecks are mostly active at night when they hunt for small salamanders, insects, slugs, and any other animal that can fit down their gullet. They, in turn, are preyed on by larger snakes, raccoons, and, occasionally, birds. I’d guess, from the smell, that they taste pretty bad. I usually encounter them under rocks and logs. The contrast between their smooth dark backs and bright bellies makes them one of the more visually appealing (I was going to say…striking…but we’ll leave that word for the copperheads) snakes in our area.

Range maps for the species indicate that this is a “northern” ringneck. But the color patterns are ambiguous. The animal has a complete neck ring (a characteristic of the northern subspecies, D. p. edwardsii), but the belly is patterned (a characteristic of the southern subspecies, D. p. punctatus). Some recent molecular work suggests that this “species” — the ringneck snake whose range covers much of North America — may in fact be a complex of multiple undescribed species. In addition, some of these undescribed species seem restricted to particular habitat types, suggesting ecological as well as evolutionary diversity within the group. So taxonomic revision is coming, I suspect.

Carpentry

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I’ve been using some salvaged wood to make repairs to the goat barn. One of the pieces seemed unusually light. I flipped it over and found a perfectly round hole on one side: the entranceway of a female Eastern carpenter bee, Xylocopa virginica.

The bee that left this hole used her mandibles to gnaw into the wood, then she slowly tunneled through the timber. I’ve seen these bees at work on the rafters of several of the small barns that we’ve built for animals and hay. On a quiet day in early summer you can hear the crunching of chitin on wood as the bees make their slow progress. Below the holes, small piles of sawdust accumulate.

I’ve seen many entrance holes, but never had the opportunity to see the extent of the tunnels inside. So I made a series of longitudinal cuts in my wood scrap, a 4×4 dissection of sorts. Inside, I found the tunnels extended about a foot away from the hole. One or two tunnels branched. This is an impressive hidden network, like a subway with just one exit. No wonder the piece of wood was so light.

The bees make these tunnels for their young. The female makes a ball of pollen and nectar, then lays an egg. All this is sealed into the tunnel with a slug of compressed sawdust. Once the passage is sealed, the mother leaves her offspring to their fates. These futures sometimes involve woodpecker beaks. The drilling of these hungry birds will finish what the bees started. The two species, bee and bird, are an anti-carpentry team. But I also think of these animals as supreme carpenters: they’ve been making homes from wood for millions of years and they spend their lives happily sprinkled with the sawdust of their labor. So they are both über- and anti-carpenters.

Away from wood, the bees do good work as pollinators. They are eager visitors to many species of flowering plant. Some farmers even erect pieces of wood to attract them into their orchards. I’m OK with a few at our place, but a year ago we had an invasion of battalions of barn-destroyers. So I relived my glory days of college squash-playing, dispatching them with a killer backhand from a dustpan. I felt bad, but not as bad as I would have had the barn needed rebuilding. These days we just have a few carpenter bees buzzing around and I leave them alone.

The Forest Unseen — readings from the woods

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I’ve posted some short readings from The Forest Unseen on the book’s website. I recorded these excerpts in the woods, sitting at the same small area of forest that is the book’s focus. Unlike studio recordings, these audio clips have plenty of background noise, especially cicadas. That seems fitting, given the book’s setting and subject matter. After all, one of the themes of the book is that the world’s “background noise” is worth hauling out of the background and into our field of attention.

I have one or two more audio files in process…so I’ll post more next week.

Shakerag Hollow: damage from construction continues

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I visited Shakerag Hollow this afternoon to make some sound recordings. A good thunderstorm blew in, giving us another inch or so of rain. Unfortunately, on my walk out, the intermittent stream near Green’s View was running the color of milky coffee. I walked up to the construction site and found water pouring off the bare ground, hitting a construction fence, then running underneath, and into the woods. The fence added about 30 seconds to the water’s travel time, so it would be technically incorrect to say that the barrier did nothing. Just next to nothing, in my opinion.

Disturbed by this sight, I diverted my return walk to look at the larger drainages. On one, the retention walls and sodding did seem to have slowed the rate of soil loss. The water running off was dirty, but not completely opaque as it has been. But on the largest drainage, water ran right through the rock walls, across the small ponds, and straight out into the stream leading into Shakerag.

So the streams of Shakerag Hollow, and the waterways into which these streams flow, continue to be severely impacted by the golf course construction that I discussed in a previous post.

Looking from the edge of the construction into the woods. This flows directly into the stream near Green’s View.

The main flow from the golf course leads to a series of waterfalls.

Water running under and through rock walls.

Muddy retention pit. Water flows directly out of this pit into the stream.

This water runs into the woods and a stream, slowed slightly by having to go under the construction fence.

“…somewhere about the middle of the month when suddenly there’s a foretaste of fall”

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This morning, my friend Bill Keener sent me the following words from Faulkner. They relate directly to the bodily experience of the past few days, so I though I would share them here.

The quote comes from a 1957 question-and-answer session in an American Fiction class at the University of Virginia. You can hear digital audio clips of portions of the session here.

Question: “You spoke of titles before, Mr. Faulkner. I’d like to ask you about the origin of Light in August.”

Faulkner’s answer: “Oh, that was—in August in Mississippi there’s a few days somewhere about the middle of the month when suddenly there’s a foretaste of fall, it’s cool, there’s a lambence, a luminous quality to the light, as though it came not from just today but from back in the old classic times. It might have fauns and satyrs and the gods and — from Greece, from Olympus in it somewhere.  It lasts just for a day or two, then its gone, but every year in August that occurs in my country, and that’s  all that title meant, it was just to me a pleasant evocative title because it reminded me of that time, of a luminosity older than our Christian civilization…that light older than ours.”

If this seems an overblown response to a cool day in August, remember that Faulkner lived in Mississippi, without AC. For months, life was lived under a sheen of sweat. Any exertion, even in the relative cool of morning, would soak a shirt. At night, lying immobile in bed, tiny rivulets pool in the hollows of collarbones. And the light? A haze of water drawn into air. So when these August days come, the texture of life is transformed. The heat-fogged light snaps into clarity. The simple pleasure of working outside all day and barely breaking a sweat takes on a mythic quality — the body is transported, abruptly, to another world.

Earthstar

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Indulge me by letting me start with a short quote from The Forest Unseen:

“August 8th — Earthstar. Summer’s heat has coaxed another flush of fungi from the mandala’s core. Orange confetti covers twigs and litter. Striated bracket fungi jut from downed branches. A jellylike orange waxy cap and three types of brown gilled mushroom poke from crevices in the leaf litter. The most arresting member of this death bouquet is the earthstar lodged between rafts of leaves. Its leathery outer coat has peeled back in six segments, each segment folded out like a flower’s petal. At the center of this brown star sits a partly deflated ball with a black orifice at its peak.”

And, several years later, right on cue in early August, here are the earthstars in Shakerag Hollow. They must be the most gorgeous fungi ever. The one pictured above is Geastrum saccatum. It is about the size of a quarter.

My essay in The Forest Unseen rambles off in the direction of golf balls. Here I’ll keep my eye on the fungus.

Earthstars belong to the Gasteromycetes (“stomach fungi”), a motley collection of mushrooms that hold their spores in a stomach-like sac. Other members of the group of puffballs, stinkhorns, and bird’s nest fungi. Unlike the gilled mushrooms, bracket fungi, and others that forcibly eject spores using microscopic catapults, Gasteromycetes take an entirely passive approach to dispersing their spores. They hope for a raindrop, or the step of a beetle, or a prod from a falling twig to puff their spores into the air.

The evolution of these Gasteromycete fungi reveals some interesting evolutionary processes. Once the “stomach-like” form evolves, there is no turning back. Although “normal” gilled mushrooms have evolved earthstar or puffball-like structures at least four times, there are no known evolutionary transitions in the other direction. Why? The catapult mechanism is so complicated that it is very unlikely to re-evolve once it has been lost. After the catapult genes have been discarded, only a very long stretch of time and some lucky mutations could bring them back.

The loss of forcibly discharged spores has unexpected consequences. It turns out that having a passive spore dispersal mechanism makes a species more likely to split into new species. Exactly why this should be so is not clear. Perhaps their spores do not travel as far, so allow populations to become isolated from each other, leading to reduced gene exchange and then speciation? Regardless of the mechanism, the Gasteromycete fungi have been speciating more rapidly than their gilled relatives.

So the future belongs to the earthstars. Especially those that can figure out how to eat golf balls.

____

For those interested in digging deeper, the relevant articles in the scientific literature are listed below.

Hibbett, D. S., E. M. Pine, E. Langer, G. Langer, and M. J. Donoghue. 1997. Evolution of gilled mushrooms and puffballs inferred from ribosomal DNA sequences. Proceedings of the National Academy of Sciences, USA 94: 12002–6.

Wilson, A. W., Binder, M. and Hibbett, D. S. (2011), Effects of gasteroid fruiting body morphology on diversification rates in three independent clades of fungi estimated using binary state speciation and extinction analysis. Evolution, 65: 1305–1322. doi: 10.1111/j.1558-5646.2010.01214.x