Reciprocal Flows

There has been a traditional divide between the worlds of water and dry land in ecology and management, one that has greatly impeded our understanding of the linkages between the two, and long prevented us from realizing, once again, that the artificial divisions we place upon our perception of the world in an attempt to make it easier for us to understand or manage are just that- artificial.  I realized this more fully when I first began to work with the land we owned along the creek north of town.  At first it seemed straightforward enough.  There was creek, and there was upland, and there was only a narrow ragged remnant of forest running along the banks.

It is a fairly short creek, only a few miles from headwaters to its confluence with a small river.  The source is on the major ridge to the north of us.  From there, the creek cuts quickly downslope until it reaches the valley floor not far upstream from us.  The creek slows down a bit there, taking the time to begin to meander, and it supports a nice riparian woodland of bigleaf maple, pacific ninebark and Indian plum, and wildflowers such as delphinium and trillium.  By this point, the creek is big enough to throw a good temper tantrum during a winter storm, and of maintaining a base flow during the summer drought.  Both are important not only to the life of the creek, but to the life of the forest as well.

The riparian zone upstream. Photo: J. A. Gervais

The water doesn't just come from the channel coming down from the north.  There are numerous seeps along this section of the valley, places where suddenly sedges bristle up, where you can sink a tractor up to its axle before you can blink (we've done that).  Fencepost holes sometimes filled with groundwater within minutes, making us rethink the placement of fence lines.  This water is coming from the ridges that run to the west and east, traveling below the surface for perhaps a kilometer or more before bubbling back up into daylight. Some of it likely comes up right in the creek bed.  This is known as hyporheic flow.  It means there's more to the creek than the channel, and that wearing mud boots is generally a good idea even in the meadow.

I've been slowly bridging the divide in my formal education, reading more about just how much a mix of upland and aquatic worlds a riparian zone really is. Large woody debris slows the flow of water, allows sediments to settle, and provides pools.  There isn’t any large wood in our section of creek, because there haven’t been large trees to provide it for many years, and it probably was dragged out if it had fallen in.  There isn’t much of a floodplain here anymore either, because the creek has cut a channel too deep to climb out of in all but the worst floods.  The end result is a truncated system, created from historical misuse.  The floods this past January, however, began to pile up debris and created side channels, the first signs of returning complexity in our section of creek.  Maybe we're getting somewhere, reestablishing the connections between aquatic and terrestrial, past and present.

 Creek bed after the floods rearranged it.  Photo: J. A. Gervais

This patch of land has been farmed for decades.  The last people who lived here rescued abused horses, and fenced in a broad wedge that included the creek.  The horses, over a dozen of them, trampled the banks and stripped the trees, until only a thin, wavering line of vegetation remained.  When the horses left, invasive blackberry thickets grew to over ten feet in height, choking out any hope for new native trees and shrubs.  But this creek has been designated a possible salmon stream, and landowners along the length of it have been encouraged to restore the riparian forest that once graced the length of its banks.

The forests along waterways support the life in the water, which in turns provides resources to the life on land.  Hatches of aquatic insects such as mayflies don’t just feed the fish, but they also support the birds and bats and spiders living along the banks.  In turn, terrestrial insects and plant matter falling into streams and rivers provide major sources of nutrients and energy to the aquatic community.  In fact, one study suggested that nearly half of the annual diet of rainbow trout was made of insects that fell into the stream.  The terrestrial insects are strongly affected by the vegetation along the waterway.  If we wanted to see salmon return, we needed to plant trees.  I had just plunged across the terrestrial/aquatic divide.

 Future ash swale, four years after planting.  Photo: J. A. Gervais

We mowed down the blackberry and with a good number of friends, planted over a thousand native trees and shrubs into the two acres along our section of creek.  Things are looking up.  The planted trees and shrubs have done pretty well, especially the willow.  Even more encouraging, a number of tough volunteers have sprung up from the areas once smothered by blackberry.  We’ve found banana slugs and rough-skinned newts on our property.  We’ve heard frogs in the seeps along its banks and seen fish and invertebrates in the water.  We’re not back to the conditions that existed a hundred and fifty years ago, but they're probably better now than in any point during the past three quarters of a century.  We hope the trend continues beyond our ownership.

Although you can’t stand in the same river twice, the continuum of history and geography shapes the water flowing around your legs.  There is still old farm junk caught in the creek bed, sheets of sediment twisting and crumpling against the bits of rooted rusting iron.  The fence line is new, barely five years built.  When we put the fence in, it was set far enough back that there was easy safe distance from the wire to water.  The creek has looped toward the fence since then, maybe wanting to add more metal debris to its collection.  The creek already reclaimed the lower pasture corner during that violent storm last January, jumping out of its bed and sweeping an arm across the grass, depositing silt from the high ridge.  Remember what's happened before, what came and went, where proud accomplishments failed.

 The tenuous boundaries between terrestrial and aquatic systems. Photo: J. A. Gervais

What we do on the banks of a river affects what happens between those banks, but it’s all pretty temporary in the lifespan of moving water.  In the end, erosion will wear down the divides.


Resources:

• Baxter, C. V., K. D. Fausch, and W. C. Saunders. 2005. Tangled webs: reciprocal flows of invertebrate prey link streams and riparian zones. Freshwater Biology 50:201-220.

• Gregory, S.V., F. J. Swanson, W. A. McKee, and K. W. Cummins. 1991. An ecosystem perspective of riparian zones. Bioscience 41(8):540-551.

• Iwata, T., S. Nakano, and M. Murakami. 2003. Stream meanders increase insectivorous bird abundance in riparian deciduous forests. Ecography 26:325-337.

• Kawaguchi, Y. and S. Nakano. 2001. Contribution of terrestrial invertebrates to the annual resource budget for salmonids in forst and grassland reaches of a headwater stream. Freshwater Biology 46:303-316.

• Kawaguchi, Y., Y. Taniguchi, and S. Nakano. 2003. Terrestrial invertebrate inputs determine the local abundance of stream fishes in a forested stream. Ecology 84(3):701-708.

• Laeser, S. R., C. V. Baxter, and K. D. Fausch. 2005. Riparian vegetation loss, stream channelization, and web-weaving spiders in northern Japan.  Ecological Research 20:646-651.

• Nakano, S., and M. Muraami. 2001. Reciprocal subsidies: dynamic interdependence between terrestrial and aquatic food webs. Proceedings of the National Academy of Sciences 98(1):166-170.

The various contrivances of orchids

I joined the local orchid society this winter.  The months of soggy dark require unusual coping measures at times; the displays of blooming orchids on the "show and tell" table at the monthly meetings alone are worth the membership.  My own little collection isn't doing too badly.  My phalaenopsis and paphilopedilum are blooming, and the zygopetalum's buds are swelling steadily. 

Phalaenopsis, known as the moth orchid.  Photo: J. A. Gervais

Orchids make up the largest plant family on the planet, with about 24,000 species.  They live in a staggering array of environments, from the tropical rainforests most of us associate with them to tundra environments, in the deep shade and out in the open sun, perched in trees or on the ground.  They are united, however, in their extraordinary biology, making use of an incredible array of other organisms to help them through their life cycle.

The local orchid society has about thirty members, small enough that guests are immediately recognized as such and welcomed with enthusiastic delight.  How do you not join a group of people who love to talk about flowers?  The skill level ranges from experts who hone their skills cultivating the most challenging plants, to people like me who can kill just about any orchid effortlessly.  I suspect the experienced growers look on us neophytes as a great way to clean out the clutter of their greenhouses: giving an extra orchid to someone who at least admires it seems less heartless than throwing it straight on the compost heap.  I view it as a type of symbiosis, although the plants may not.

Orchids have developed trans-species  interrelationships to a remarkable degree on several fronts.  The seeds require the services of a mycorrhyzal fungus in order to germinate, relying on the fungus to make up for their lack of endocarp.  Many species are epiphytes, perching on the trunks and branches of larger plants.  The pseudobulbs of other orchids harbor ferocious ants that offer protection to their hosts.  Most noteworthy, some orchids have developed extraordinary coevolutionary relationships for pollination.

Anagraecum sesquipedale.  Charles Darwin hypothesized that this magnificent orchid is pollinated by a hawk moth.  The moth, Xanthopan morganii, wasn't discovered for another 41 years, and proof of pollination services had to wait 130 years after Darwin's insight.

Although many flowering plants have built relationships with animals for the purposes of both pollen delivery and seed dispersal, orchids have gone to extremes.  The pollen of the vast majority of plant species is released as a dust of individual grains, but in nearly all orchids pollen is wadded up into two to twelve waxy balls, called pollinia.  It's a high-risk strategy, because each flower on the plant (and many produce only a single flower) has exactly that many chances to fertilize another plant's flowers for seeds.  It's a twist on putting all of one's eggs in a very few baskets.

The pollinia are designed for long-distance transit.  Pollinia on hawk moths in the wild have remained stuck in place and ready for deposit for over three weeks.  Insects, birds, and moths that visit orchids may have multiple pollinia stuck to their heads, beaks, and proboscuses like yellow bunny ears.  Different species of orchids place their pollinia in slightly different positions on the pollinator, ensuring correct delivery when the animal visits the appropriate orchid species again. 

This trait can be quite useful for someone interested in propagating orchids, and in creating new hybrids.  It isn't hard to use a pencil or other pointed object to lift the pollinia free of the flower column; they will quickly bind tightly to the object and orient themselves for maximum contact with the receiving flower's stigma.  It is a system easily manipulated by people.  In fact, we're the only mammal that pollinates orchids.  Once fertilized, the flowers quickly wilt.  This, announced my high school biology teacher with a wicked grin, opens up interesting possibilities if you don't like the prom date to whom you are expected to offer an expensive orchid corsage.

The flowers are all about sex, as all flowers are, but for some orchids it's a double entendre.  The sneakiest orchids are those whose flower parts have evolved to resemble female insects, complete with a release of chemicals that mimic the insects' own pheromones.  The strategy is known as pseudocopulation, as the befuddled male insect attempts to copulate with the flowers, and gets tagged with a pollinium for his pains.  Presumably he either doesn't learn, forgets quickly enough, or becomes desperate enough to visit another orchid of the same species before he dies.  The odds are long, and because of that the flowers remain intact for many weeks.  This is, of course, one of the characteristics that makes them so irresistable to humans bent on romance. 

The aptly named bee orchid, Ophrys apifera.  It is pollinated by male bumblebees and is an example of pseudocopulation.  Photo by Nancy Cottner

Not all orchids try to forgo paying the pollinators for their services through deceit.  Many offer nectar, which varies in sugar concentration depending on the pollinator. Specialized avian pollinators such as sunbirds earn the highest reward; hawk-moth-pollinated flowers offer a somewhat lower sugar level, and the least concentrated nectar is payment to the least-specialized pollinators from the more generalist orchids.  Within the flower, the most concentrated nectar is the farthest in, encouraging a good push to obtain the reward, and maximum contact with the pollinia.  Other orchids offer scents or waxes and resins that are gathered by their pollinators.

My fellow orchid enthusiasts range from generalists who do not seem to have ever met an orchid they didn't like, to those who specialize on one small subgroup.  Some folks seem taken up entirely by the challenge of the cultivation of the most exacting varieties, whereas others of us are unapologetic fans of the lowest-maintenance plants that reliably produce bright, interesting blooms with the least amount of fuss.  We're all in it for the flowers. 

For all their trickery and bribes, less than one in five tropical orchids typically achieves fruit set in the wild.  Pollination is generally thought to be the limiting factor for reproduction in wild orchids, even with their absolute dependence on fungi for seed germination.  Wild orchids are perhaps most amazing in the fact they exist at all, let alone having successfully woven themselves into the ecological fabric of so many places.

The orchids on the monthly show and tell table are often so hybridized by human breeders that the names of the crosses don't always fit on the plants' tags.  These are organisms of the greenhouse and windowsill, depending on the passion, space, and financial allocations of the owners.  I asked one of my fellow club members how many plants he had.  "Seven hundred, I think," he answered.  "I have two greenhouses now.  We all started with a few orchids on a windowsill."  Orchids have been amazingly successful at bending yet another species to the task of continuing their existence. 

I swear my little collection isn't going to need more space than my windowsills.  Soon, after the peas have sent up tendrils and the lambs have all been born, I'll be out in the woods hunting for my favorite orchid: Calypso bulbosa, which grows in heavily shaded understory, and tricks bumblebees into pollinating it.  I don't have to do anything at all, except admire it and the extraordinary ecological relationships that sustain it.  I don't think, however, that either the club members or their orchid masters have given up on me.

Calypso bulbosa.  Photo: J. A. Gervais

Sources:

Boyden, T. C. 1982. The pollination biology of Calypso bulbosa var Americana (Orchidacea): initial deception of bumblebee visitors.  Oecologia 55(2):178-184.

Cozzolino, S., and A. Widmer.  2005.  Orchid diversity: an evolutionary consequence of deception? Trends in Ecology and Evolution 20(9):487-494.

Darwin, C.  1882.  The various contrivances by which orchids are fertilized by insects. 2nd Edition, Revised. London: John Murray.

Micheneau, C., S. D. Johnson and M. F. Fay.  2009.  Orchid pollination: from Darwin to the present day. Botanical Journal of the Linnean Society 161:1-19.

Tremblay, R. L., J. D. Ackerman, J. K. Zimmerman, and R. N. Calvo.  2005.  Variation in sexual reproduction in orchids and its evolutionary consequences: a spasmodic journey to diversification.  Botanical Journal of the Linnean Society 84: 1-54.

Driloleirus macelfreshi lives!

This week marked the third anniversary of a significant scientific discovery made by my dogs.  We were out on a walk on a messy afternoon marked by mud, driving rain, and wind, courtesy of a Pacific winter storm.  Young dogs still need their walks, and so do their owners.  I can't really say quite how it happened, other than as I bent down to discharge my responsibility as a dog walker after my old dog had finished her business, I glanced back and saw the young one standing with a long pinkish stringy thing hanging from his jaws.  He looked quite pleased with himself, and was an instant away from flinging up his head and consuming his prize.  I witnessed this in the split second between discovery and annihilation. And somehow I knew that he absolutely must not be allowed to eat this thing, not for any risk to himself, but because of what it was. 

I leaped at him, howling at him to drop it, which is absolutely not how you are supposed to train a six-month old pup to surrender highly desired objects.  Fortunately for science, he was so shocked at my behavior he did drop it, and in his moment of indecision I swooped on his find and scooped it into a spare plastic bag.  The dog was utterly unimpressed at my inexusable theft of what he regarded as rightfully his.  There are times when I wonder whether he still remembers this.

At that time, however, we went home, and I laid the dog's find out on the counter.  It was an earthworm, and it measured four feet four inches long.  It was flabby, pale pinkish-gray, impossibly thin, and quite dead.  It was also the first specimen of the Oregon giant earthworm, Driloleirus macelfreshi, to be documented in twenty-seven years.  We know very little about this species, other than it seems to be endemic to the wooded bottomlands of the Willamette Valley.  It had been pretty much assumed to be extinct.

There are many little pieces to this discovery, each of which made that sudden, instinctive recognition on my part possible.  Over a decade ago, I had the great fortune to meet two of the last earthworm taxonomists in the world, Dorothy McKey-Fender and her son, Bill Fender.  This in itself was a culmination of improbable circumstances, but the crux was a workshop, conducted by Dorothy who was then in her eighties, on how to identify native earthworms.  The workshop was followed by a search for native worms in 2000.

Bill Fender and Dorothy McKey-Fender with a specimen of Driloeirus macelfreshi in their laboratory in 2000.  Photo: D. K. Rosenberg

I know a little about earthworms, as much probably as any average gardener or curious naturalist knows.  Native worms have been largely replaced by exotic species, and most of the worms we see as we go about our daily lives are descendants of recent immigrants to this continent as most of us are.  Ecologically speaking, we do not even know what we've lost, because the native worm fauna has been very poorly studied and described.  We do know that different families of worms behave differently, and affect nutrient turnover and soil humus in different ways.  We do not understand all the implications, although they include reducing the humus layer, which is itself a vital habitat for many organisms, and allowing exotic weeds to establish on the surface of soil no longer protected by that deep blanket.  For the most part, though, we just don't know what we've broken or what pieces remain somewhat intact.

There are earthworms out there, native worms, very different from the nightcrawlers we all immediately identify as the ultimate worm.  Even more amazing, there happens to be a gigantic native worm called the Oregon giant earthworm, Driloleirus macelfreshi.  Dorothy McKey-Fender herself had studied most of the specimens that have ever been collected- a scant few dozen in all.  They were far too rare to allow the workshop participants to examine, but Dorothy moved around the lab room set up with dissecting scopes and trays filled with other worms pinned to the black wax, delighted to share some of the knowledge accumulated over a lifetime.  Her love and respect for these animals was palpable, and her excitement contagious.  I've been more aware of worms since then, for their own sake, not just for what they do.

So there we were, in a wet riparian forest at the tail end of a storm dumping heavy rains, swelling the Willamette River until it licked and curled at the bases of the cottonwood trees along its banks.  A party of several people and several dogs ahead of us had walked right by the corpse of the giant worm lying on a bed of fallen leaves, not far from the floodwater's edge.  I would not have noticed it either, if my young dog hadn't loved to eat dead things.  But at least in that instant of seeing it, I was open to the existence of giant native worms.  Without that, the discovery would not have been possible, even if I had still looked straight at my dog in that instant before he snatched and swallowed.

Looking for another giant worm- the last one was right around here somewhere...

The worm is now among those in the McKey-Fender collection, although a small segment of the tail sits in a vial on my desk for possible genetic analysis.  More importantly, we know we can still look along the rivers and woods and hope for more than we recently dared hope for, that one of the unique forms of life on this planet may still be with us.  If we can be open to those possibilities, I hope we can also be open to more creative visions of how to live more gently and equitably among all of our fellow species.

Unintended Consequences

She kicked hard, flailing her sturdy legs madly, just missing my restraining hands.  She didn't have much of a range of motion because of her shell, but that didn't stop her from trying, stretching her neck around to snap at my fingers.  Once her hind leg kicked my wrist, and I was startled by how strong she was.  I had a good grip, however, and what happened next was my decision, not hers.

The turtle in my hands was a red-eared slider.  Like me, she was a native of the eastern half of the country.  I had come west a quarter-century ago, seeking broader horizons, while she had arrived here thanks to the pet trade. Whether she had once been released by a well-meaning but misguided pet owner who no longer wanted her, or had been born wild herself, I couldn't tell.

Red-eared slider, Trachemys scripta, basking in non-native waters.

It's against the law in many states to release non-native pets, and red-eared sliders are not even legally sold in Oregon in the first place.  But they're here, and they have found Oregon's waters to be enough like home to settle down and raise large families.  We don't really know all the potential consequences of this, although there is evidence that the native turtles don't do well once they're forced to share their space with this new arrival. 

My scientific permits specify that I cannot release any non-native turtles if I catch them.  This is meant to help remove the invaders, and give the native species a better chance of survival.  It isn't about just the individuals, or even individual species, but the sum of all the plants and animals, and the unique communities they form.  These communities can affect how water flows, how frequently and severe wild fires will burn, and whether soil will be swept away before the wind.  These processes are of fundamental importance to our well-being, if not our very survival.

I hold another set of permits, this set from the university.  These specify how I must handle individual animals in order to reduce any pain or suffering.  I have stated exactly how I'll keep any sliders I catch, and for how long, before delivering them to the state veterinarian for what amounts to their execution.  Under those conditions, the Institutional Animal Care and Use Committee gave me permission to proceed.  This set of permits is not at all concerned about ecological processes, but it is deeply concerned with the welfare of individuals.

There are very good reasons for both permits.

Turtle trap with red-eared slider inside.

Personally, I happen to really like animals.  I happily share my house with two dogs and a geriatric cat and there would be more if it didn't mean serious strife with my husband.  We raise sheep and goats, and the fact we slaughter our own meat makes us acutely aware that living beings are individuals, each with their own perspective and purpose.  I do not take killing lightly.

As a professional, I am only too aware to how careless introductions have changed everything from the composition of trees in the forests in much of the country to the soil dynamics beneath my feet.  I don't know if red-eared sliders will end up being the biological equivalents of neutron bombs in Oregon's aquatic systems, although they will have impacts.  I suspect probably not, although other invasive species may deserve the comparison.  However, I am not a policy maker, and it is not my call.  The law, and my permits, are clear.

Yet it is amazing how the ancient instructions for life have adapted these turtles to an utterly new place, one dominated by humans.  Sliders are doing fine here, and may do better still as the Pacific Northwest climate shifts to warmer and drier weather.  At some point, we may need to choose based on what can exist in the future, rather than what existed in the past.  The changes we're bringing about on our planet are so great that asking these questions is no longer only the business of theoreticians.  What do we want our future world to look like, given our past actions, and the choices we now have?

That is the big picture.  The small picture is me, holding this turtle, next to a drainage ditch near the airport, on a cool overcast windy day.

It isn't the turtle's fault.  She was only following the instincts that have carried her kind forward for millions of years before she swam into the trap baited with overripe sardines.  I personally didn't bring her here.  All that matters now, however, is that I have caught her, and what happens next is solely my decision.

I do what I must, based on what I know and what I have agreed to do, and she goes in a plastic bin filled with an inch of ditch water.  I wish her a quick and painless death as I look out over the landscape she won't see again.  I lug the sloshing bin to the truck.  It is a good deal heavier than a five-pound turtle, a gallon or so of water, and the container.  I am also weighed down with the ethical costs of undoing what never should have been done in the first place.

Bananas in the woods

It is finally getting warm here in western Oregon, but it is still very humid so the banana slugs (Ariolimax columbianus) are still active.  I have a soft spot for banana slugs.  The idea of a six-inch long monster yellow slug that looked like a piece of overripe fruit seemed too far-fetched to believe when I knew them only by reputation.  I was delighted to find them just as large and spectacular in life as legend made them out to be.  My interest in them from a biological point of view began while I was doing research for my Master’s degree, on the seed dispersal dynamics of salmonberry in the Oregon Coast Range.  One rainy afternoon in early June, I looked down and realized there were a dozen massive slugs slowly working their way through the tangled vegetation within the bounds of my one-meter-square quadrat.

Photo: National Park Service

That’s a lot of animal when you look at it from a biomass standpoint, even if the animal possesses a very slow metabolism.  Slugs eat everything, from fungus and fruit to their dead kin and other animals’ feces.  Mostly they are herbivores.  Work in the 1970s demonstrated that slugs can affect plant community composition in the forest understory.  They also act as a host to a number of generalist parasites (another good reason not to eat one, even if the slime didn’t put you off), and they likely disperse the spores of fungi as well.  In other words, slugs do stuff to their environment. 

I found salmonberry seeds in their droppings and asked the obvious question: are they seed dispersers, or seed predators?  I set up ten Tupperware slug houses, raided the nearby forest for volunteers for science, and kept ten slugs going on potato, carrot, and fresh lettuce in addition to the salmonberries and other wild fruits in my living room.  You could actually hear the slugs chewing.  Fortunately, my roommate thought this was intriguing if a bit weird.  After the animals obligingly ate a series of fruits from the local forest, I let them go, perhaps a bit fatter than they were before.

Salmonberry (Rubus spectabilis) and its two color morphs. Photo: J.A. Gervais

I planted the seeds, and discovered that banana slugs do disperse viable seeds, although their gut kills some of them.  Interestingly, red salmonberry seeds were more likely to die during gut passage than orange ones.  All of the other seeds from native plants producing fleshy fruits also were capable of germination.  I tried to use the word “molluschrory” to indicate this novel dispersal agent of seeds, but my co-author on the paper, ecologist Mary Willson, shot that down.  It is hard to have your tongue in your cheek in a scientific paper, apparently, and have others get the joke.

Slugs aren’t the most spectacular seed dispersers, because in the twenty four hours that it takes them to pass a seed, they don’t go very far.  In fact, slugs have fairly small home ranges with a number of shelters that they will return to repeatedly, following their own slime trails around their neighborhood.  The slime they secrete under the muscular foot is astonishing in itself.  Slugs change the chemistry of the slime according to their needs, secreting a more watery version when traveling along the ground, a tough cord they use to rappel down from the heights of a shrub, and thick viscous goo to deter predators.  They can change the composition of the slime to fit the circumstances, and the chemistry can be altered in a matter of minutes.

Predators can track the slugs from their trail of slime, so their trails may work against them.  One slug, the jumping slug (several species in the genus Hemphillia) actually twists off its slime trail, breaking the chain of evidence a predator might use to track it down.  Another slug, the tail-dropper of the genus Prophysaon, drops a bit of its tail to distract a predator while it makes its getaway.  I am not making this up.  The banana slug has no such defense, and must either outrun or hide from its enemies, which include predatory ground beetles, snakes, Pacific giant salamanders, and even other slugs.  You can blink more than once while watching a predatory slug hot on the trail of a fleeing banana, but it is still a race of life and death for the participants.

The magnificent blue-gray tail-dropper (Prophysaon coerleum), photo: USDA Forest Service

Scientific literature is not often very amusing, but one of the best papers in my collection describes how to individually mark slugs by freeze branding them.  The publication included illustrations of miniature brands and instructions on how to use dry ice to do the deed.  The spotted slugs’ markings are unique to the individual, so photographic records work for identifying them.

Getting to know slugs as individuals revealed that banana slugs can reach at least six years of age in the wild.  They aren’t prolific egg layers, relying on their longevity to produce enough young to carry the species.  Simply put, a nice-sized banana slug may be older than the vast majority of mammals on earth.

 The study of banana slugs pretty much petered out 30 years ago, although the Northwest Forest Plan did at least pay them lip service in terms of requiring that forest managers survey for them.  It is good to remember there is a great deal we don’t know about our fellow travelers, even the ones right underfoot.  Step carefully.