Backyard Boa

Billie appeared at my doorstep in the heat of the afternoon, her hands cupped firmly together and held against her body.  "I've got a boa," she said.  "It came out of a weedy area I was mowing, and I don't want it to get into the road.  Can we release it in your rock wall?"

By all means.  The elusive rubber boa, Charina bottae, is one of those common and utterly overlooked creatures that echos greater things.  It is the small and nearly invisible cousin of the impressive anacondas, pythons, and boa constrictors, massive snakes large enough to eat small deer and peccaries.  The boa family line has some unusual characteristics among snakes.  The members carry two lungs, rather than the single lung considered adequate by most snake species, and boas retain their eggs in their bodies, giving birth to fully-formed young rather than laying the eggs like many other snakes do.  For the uninitiated, boas hunt by lunging out at unwary animals, encircling their prey in coils of their thick, smooth bodies, and strangling their dinner.

 

Rubber boa. Photo: J. A. Gervais

But the boa family is probably most noteworthy for another reason: they are snakes with legs.  They still retain the tiny nubs of what were once fully functional limbs.  Both sexes carry small spurs placed along their sides above the vent, used primarily by the males in courtship. 

The northernmost branch of the family ranges into North America in the form of two species, the rosy boa and the rubber boa, which extends up into British Columbia.  These are the poor cousins of the spectacularly patterned and impressively sized South American relatives.  The rosy boa boasts some handsome stripes but its northern cousin, the rubber boa, is notable for its plainness and the fact they occur in a wide variety of habitats although they are rarely noticed.  The body is olive or brown or pinkish, the belly lighter and possibly more shaded with yellow, and there are no lovely patterns of brown or black or green, no rings or stripes or spots or really anything of interest at all.  Their scales are small and very smooth and hardly offer any texture to break the monotony of their skin.  All in all, they are spectacularly uninteresting, other than the chance to see those relict legs that are now reduced to small spurs.

Except for two things: rubber boas have tiny eyes.  And they have thick, knobby tails that are as large as their heads.  With the very fine scales and tiny eyes, you might mistake one for a large fat worm.  The legs are pretty surprising, but they're easy to overlook.

Rubber boa head. Photo: J. A. Gervais

Rubber boas spend much of their time underground, haunting rodent burrows and cracks in the earth, sheltering under appropriate human junk.  They seem to do much of their hunting at night, and they are the scourge of the cozy nests of mice, shrews, and other small mammals.  The snake will eat all of the babies if it can, holding the mother at bay with that thick, knobbed tail.  One report also documents a snake consuming both a mother ensatina salamander and her clutch of eggs, which the salamanders brood until hatching.  These snakes are the real cradle-robbing monsters of nightmares.

 However, the boas themselves are often heavily scarred, and some voles and mice will counter-attack repeatedly to defend their offspring.  They may even kill the attacking snake if the snake is a small one.  Bigger boas will also eat birds if they can catch them, and smaller snakes feed on the eggs of other reptiles.  There are reports of big boas trying to eat smaller ones, although these incidents were seen in captivity.  There's a lot of tabloid-style drama going on out in the fields that we never notice.

Billie put out her hands and slowly opened them so I could see the boa.  It was olive in color, with a yellowy underside, about two feet long, and much more interested in hiding its head and presenting its tail to us than escaping.  The rubber boa is also one of the most docile of snakes, moving slowly and nearly impossible to provoke into biting.  They are far more likely to release musk from their vent to deter rough handling, and need to be harassed to do even that.

Down a mouse hole. Photo: J. A. Gervais

Rubber boas in the northwest breed in early spring.  The spurs are part of the courtship ritual, used primarily by the male snakes, whose spurs are more mobile.  Females' spurs are also more conical in shape, where the male snakes have spurs shaped like hooks.  Adult females are larger than males, with shorter tails, and more tail scarring, possibly because the demands of producing young require more hunting.  Females may not eat the entire summer that they are carrying their young.  Instead they seem to spend as much time as they can keeping their body temperature as high as possible to speed the babies' development and birth.  They will be born in August, not long before temperatures drop and all of the snakes must find sites to spend the winter.

Rubber boas are homebodies, frequently caught over and over in the same small area year after year.  They are also impressively long-lived, perhaps reaching a half-century even in the wild.  Their habit of rarely showing themselves in the open keeps them safely off the roads that take the lives of so many garter and gopher snakes, and helps ensure their reputation as the boa you never knew about living right in your backyard.

We looked the snake over closely but missed seeing the spurs, which I didn't know about at the time.  The snake might well have been a female, whose spurs are hardly larger than her scales and may not even be visible.  We released it in the grass not far from the half-buried line of concrete rubble that runs along the edge of our yard, the remains of an old barn foundation we had recycled into snake habitat.  There are too many mouse droppings in the bike shed.  I hope this snake sticks around.


References:

•  Dorcas, M. E., and C. E. Peterson. 1998. Daily temperature variation in free-ranging rubber boas. Herpetologica 54(1):88-103.
• Hoyer, R. F. 1974. Description of a rubber boa (Charina bottae) population from western Oregon. Herpetologica 30(3):275-283.
• Hoyer, R. F., and G. F. Stewart. 2000. Biology of the rubber boa (Charina bottae) with emphasis on C. b. umbratica. Part I: capture, size, sexual dimorphism, and reproduction. Journal of Herpetology 34(3):348-354.
• Hoyer, R. F., and G. R. Stewart. 2000.  Biology of the rubber boa (Charina bottae) with emphasis on C. b. umbratica. Part II: diet, antagonists, and predators. Journal of Herpetologica 34(3):354-360.
• Macey, R. M. 1983. Charina bottae food. Herpetological Review 14(1):19.
• Peabody, R. B., J. A. Johnson, and E. D. Brodie, Jr. 1975. Intraspecific escape from ingestion of the rubber boa, Charina bottae. Journal of Herpetology 9(2):237.
• Rodriguez-Robles, J. A., C. J. Bell, and H. W. Greene. 1999. Gape size and evolution of diet in snakes: feeding ecology of erycine boas. Journal of Zoology 248(1):49-58.

Manipulative Bounty

It is late summer in western Oregon, meaning the wild blackberries are just ripening, dangling tantalizingly between the wicked thorns of canes that can arch up over fifteen feet in the air.  The canes form thickets impenetrable to animals larger than rabbits.  Come and get it- just don't forget your machete and a willingness to make a small blood sacrifice.

We don't give plants much credit for intelligence, at least not as we typically define it, but the dark, sweet fruit is all about making up for the one thing plants sorely lack once they've put down their roots: mobility on a time scale relevant to getting your kids out from underfoot.  Trouble is, if you dump your offspring right around your knees, you're liable to kill them by outcompeting them, for space, water, and especially light. You are also a magnet for seed predators, waiting for the bounty to fall.  So, somehow, plants have to get their seeds away from them.

Some plants have gone the engineering route, and over time natural selection has outfitted them with pods that burst open, giving their seeds the equivalent of a blast from a cannon, or lightweight parachutes to help them drift away.  These plants don't ask for help from another living organism.  Some plants produce seeds that float to new locations, like coconuts.  Other plants have done some modified engineering, covering their seeds with sticky coatings or grapple hooks to catch a ride on any passing animal.  They are the freeloaders, getting a lift on the sly and offering no compensation for the service.

Jewelweed, Impatiens capsensis, has exploding pods, earning it a second name, touch-me-not.  Photo by Catherine Khalar

But plants with fruits definitely do ask for help from organisms that are capable of quick movement.  They pay a fee up front, and hope the agent delivers the goods as planned.  In short, fruits are a biological bribe.

The intended agents are those animals whose guts digest the fruit but leave the seeds unharmed.  The time it takes to process the meal helps guarantee a final deposit away from the parent plant, protecting the seeds both from infanticide and from the usual buildup of seed-eating insects or fungi that prey on the fruit that drops to the ground from the parent plant.  Think of an untended feral apple tree.

Some plants have evolved to rely primarily on birds to disperse their seeds.  Bird fruits are typically fairly small so they can be swallowed whole, and are often black, blue, or red and placed out on the ends of slender branches.  Other fruits appeal more to mammals, with big green or pale yellow fruits, often with an odor.  Many other plants outfit their seeds with small fleshy bodies called eliasomes, that appeal to ants.  The ants take both the seed and the eliasome back to their nests, where the elaisomes are consumed and the seeds are discarded, often in a safe underground spot perfect for germination.  Even fish eat fruit.

The fruits of salal, Gautheria shallon.  Photo by J. A. Gervais

Some fruits are simply weird, such as the osage orange.  If you've never seen one, it is a fruit the size of a softball and about as appetizing.  You need a hammer to crack one open.  The Missouri Department of Conservation considers the fruits hazardous and advises wearing hard hats in their vicinity.  In her engaging book The Ghosts of Evolution, author Connie Barlow makes a compelling case that such fruits actually are anachronisms, whose main seed dispersers were now-extinct large mammals and possibly even dinosaurs.  These fruits now "disperse" by crashing to the ground and possibly rolling away a little, sometimes helped along by flowing water.  Seed dispersal isn't an exact match of goods for services.

There are plenty of cheats, too, animals or other organisms that take the payment without delivering the goods.  My goats eat blackberries with gusto, but no seed will survive the ghastly conditions of their rumens.  Fungi readily infest fruit, and usually also destroy the seeds.  I've found that banana slugs eat fruit, but they damage a percentage of the seeds they eat, taking a higher payment than planned for their services.  The plant has to offer enough fruit to ensure that some of it falls into the right mouths- the first step, but only the first step, in the chain of events that will ultimately lead to a new plant that will someday produce its own seed.

Animal delivery may also come with a secondary benefit.  Tapirs in South America use latrines, small areas of communal relief.  Along with the rest of the waste, they deposit the seeds of the palm, Maximiliana maripa. Over time, these turn into stands of fruit-producing trees.  Tapir poop, too, seems to discourage the beetles that eat the seeds.  Ant garbage dumps are excellent germination sites for many plants.  Bear poop contains thousands of seeds which later germinate in the clumps of calling cards the bears leave behind.

Black bear fattening up on blueberries, Sol Duc wilderness, Olympic National Park. Photo: J. A. Gervais

Hot peppers are my favorite example of botanical craftiness.  Hot peppers get their kick from a compounds called capsaicinoids, which includes capsaicin.  The capsaicin triggers a specific receptor in mammals that is infamous for its response.  It is used in many different cuisines around the world, and also mace (something to think about when contemplating how spicy-hot you want your meal).  Turns out that peppers use birds as seed dispersers.  Birds can't taste capsaicinoids because they don't have the receptors- no tear-gas effect for them.  The compounds do, however, affect how quickly the birds' guts process the meal, shaping the rain of seeds over the landscape, and preventing a huge pile of seeds  from being deposited all in one place.  When that happens, most of them die from the competition.  The capsaicinoids also protect the fruit from attack by fungi, which would destroy the seeds.

The blackberries that are so common locally involve another twist.  They are an exotic species, Rubus armeniacus, originally from the Himalayas.  In open areas with plenty of sun, they can overgrow small buildings, abandoned cars, and nearly any other plant.  They also produce prodigious quantities of very tasty fruit, which feed nearly every wildlife species in the area judging by the bright purple bird droppings deposited on the car and mammal scat along trails in the woods.  Those seeds really get around.  The plant is a pernicious challenge to people trying to restore meadows, pastures, or stream forests. 

The blackberry thickets provide shelter and food to small mammals, birds, and reptiles in the forgotten wastelands that have been badly disturbed, but never rehabilitated or fully claimed by people.  At least the thickets are a good fortress against free-roaming cats, and offer a terrific late-summer energy boost to birds about to migrate.  They also provide us with an abundant supply of local fruit for the freezer, and blackberry jam in midwinter is one of the finest wild gifts we receive from the woods and fields around us.

Blackberry thicket overgrowing a roadside.  Local bunnies taunt the dogs from under this natural razor wire. 

Photo: J. A. Gervais

Life in a Sandwich Board

Imagine living in a sandwich board.  Not one you could remove, like an advertisement people parade at busy intersections, but one that is made of your own bones and will be with you for your entire life.  No bending to touch your toes.  In fact, forget about touching your toes.  Forget about curling up, sitting down, even rolling over.  You can't breathe by expanding your rib cage, instead you have to pump air into your lungs using the muscles in your throat.  Now imagine that you need to swim around in order to survive.

Red-eared slider, Trachemys scripta. Photo: J. A. Gervais

This improbable body plan is actually a pretty ancient idea, because turtles have been using it, without major changes, since the Triassic.  In other words, over 200 million years.  Good ideas simply don't go out of style, and this good idea has endured ice ages, drifting continents, the disappearance of the dinosaurs, the appearance of mammals, and the arrival of the ape with the big brain and opposable thumbs.

The shell is an extraordinary piece of biological architecture.  Formed from the ribs and the spine, it incorporates the the carapace, or top shell, the plastron, or lower shell, and the bridge, the plates that hold the two together. The hips and shoulder blades are encompassed inside the rib cage.  Ultimately, nearly half a turtle's mass is bone.

Red-eared slider, Trachemys scripta.  Photo: J. A. Gervais

Life inside the shell has its advantages, in that you carry your fortress with you.  Although the shell offers some protection, determined otters and other predators have been known to pry legs or the tail free and gnaw them off.  There are no fast getaways, and if the fortress is breached, there isn't much that the turtle can do about it.

There are other drawbacks.  Reproduction is challenging, to say the least, when both participants are dancing in suits of their own unremovable armor.  The distinctly domed carapace of the female makes things more difficult, as does the fact that most female turtles are larger than the males.  The male turtles' plastrons are slightly dished, and their front claws are extra long, to help them hang on to get the deed done.  It's an awkward affair, but one that has worked well enough for a long time.

The shell has to grow with the turtle.  Each bony plate must grow in synchrony to keep the shell in its proper shape.  Turtles lay eggs, and unlike birds, they form a clutch and lay it all at once.  All those eggs have to fit in there somewhere, which is why females have taller, more domed carapaces than males.  Too big a shell wastes energy, both in its growth and in the effort needed to haul it around.  Too small, and turtles cannot gain weight to form their eggs, carry them til laying, or get fat to survive the winter- not to mention draw deep enough inside to be safe from their more nimble, agile enemies.

Turtle shells have worked so well they've not only been around for millions of years but turtles and tortoises also occupy all continents except Antarctica, in habitats ranging from the deep ocean to deserts.  They can survive in some pretty degraded environments, appearing to be much more robust than many other vertebrates to pollution, reduced water quality, and other challenges thrown at them in recent times. 

This pond supported turtles...  Photo: J. A. Gervais

However, the ape with the big brain and opposable thumbs may be too much for them, as wetlands disappear and turtles fall victim to roadways, over harvesting, the pet trade, and other human activities.  With a little care, however, at least a few may survive for another few million years, moving through time in that same cautious, patient manner that has served them so well for so long.