If I learned anything from Honey I Shrunk the Kids, it’s that turning into a human that’s small enough to fit in a Cheerio comes with a unique set of challenges. Scorpions become even bigger jerks than when you’re normal-sized, for instance. And your dad almost eats you because you’re inside a Cheerio.

But what if your wildly irresponsible father hadn’t just left a shrink ray lying around—what if instead evolution had over the millennia shrunk you down, bit by bit, until a beetle seemed a formidable foe? For an answer to that, you’d have to ask the smallest snake in the world, the Barbados threadsnake, which isn’t even recognizable as a serpent anymore. It’s 4 inches long, about as thick as spaghetti, and looks more like a worm than a snake. And the challenges its diminutive size brings are many—save for falling into cereal bowls, of course.

First of all, there’s the matter of feeding. According to Temple University’s S. Blair Hedges, who first described the creature in 2008, the Barbados threadsnake has “a pretty narrow diet because their mouth can barely open. I mean, they’re small to begin with, but then their mouths don’t open like a normal snake. They just barely open up enough to squeeze in a little microscopic insect.”

While a lot of snakes out there are hunting prey like rodents and amphibians and birds, those things are of course far too big for the threadsnake (there are a few more species other than the Barbados variety, but for brevity’s sake I’ll just refer to it as the threadsnake). Instead, it’s limited to taking on primarily the eggs and larvae of ants and termites. Every so often they’ll go after the adults too, but typically it’s the young.

Threadsnakes are burrowers, spending their days squirming through soft soil, and that may be due in part to another problem that small creatures face. Because the extremely thin snake has a higher ratio of surface area to volume—compared to, say, a polar bear, which has a lower ratio with its bulky body—it’s more susceptible to losing moisture. By kicking back in the wet dirt, the snake can better avoid desiccation (being so bulky, by the way, also helps the polar bear better retain heat).

Also an issue is how they bear their own young. How many eggs a snake can lay varies greatly, the Eastern mud snake here in the States, for instance, can produce as many as 100, but the threadsnake is at the opposite end of the spectrum with a grand total of…one. Mama threadsnake bets on one single egg.



The Eastern mud snake is 3 feet long and pretty thick, and can thus pack all those eggs in there. But the threadsnake is so short and so incredibly thin that her body can only fit one egg at a time. And it’s a goofy-looking one: At just .08 by .5 inches, six times as long as it is wide, the egg is about the size and shape of long-grain rice, whereas most snake eggs tend to be more spherical.

This is an extreme evolutionary tradeoff. By growing so small, the threadsnake has sacrificed high fecundity, that is, how many young it’s able to produce. This is of course rather risky. We humans having a single child is one thing, since we stick around to dotingly care for it for a long, long time (well, ideally at least). But most reptiles lay their eggs and just take off. Yet here we have a tiny snake that’s been getting along perfectly fine dropping just one egg. Problem is, its life history as a whole and its ecology remain very much mysterious. For all we know the females could actually stick around and guard their hatchling like some species of reptile do. “We know almost nothing about these because they’re so rare,” said Hedges. “There’s only a few specimens that have ever been seen and collected. Nobody’s ever studied them ecologically.”

But we can be sure that there’s a very good reason why the threadsnake got so tiny: shrink rays. Wait, no. Not shrink rays.

Little Big Planet

When an island forms, it’s ripe for conquering. Plants and animals get there any number of ways: swimming, floating on debris after a hurricane, flying, blowing in the wind (spiders can float hundreds of miles by sending out silk that gets caught up in gusts). And when the first creatures arrive, they find a whole lot of open jobs in the ecosystem just asking to be taken, known as niches. And those new jobs aren’t necessarily the ones the critters had back on the mainland. This may have been what happened to the threadsnake. “This species, even though it’s a snake,” said Hedges, “it could be filling a niche of a smaller invertebrate like a centipede or something like that on the mainland.”

Now, some species tend to be rarer on islands than other groups. This is because the journey on debris would be far more difficult for something like a mammal or an amphibian than, say, beetles, which are fantastic at retaining moisture. So it could be that the threadsnake’s ancestors arrived on Barbados, while their typical prey failed to make the journey. Over evolutionary time, the threadsnake adapted to take on different game, and became so specialized that it just may have reached the smallest possible size for a serpent. (By the way, there was once a snake that got to what’s probably the largest possible size. This was titanoboa, which grew to almost 50 feet long and 2,500 pounds, 2 million times heavier than the threadsnake. It pushed the boundaries of what the laws of physics actually allow—gravity was such a drag on the creature that it probably spent the bulk of its time in the water.)

So islands tend to really monkey with species’ sizes. “The story here is because you see the smallest and largest animals quite often on islands—there are tiny elephants on islands in Indonesia, the largest lizard the komodo dragon on an island, the smallest lizard is on an island in the Caribbean—the reason you see this pattern is because of the niche vacancies.”

The evolution of the threadsnake just got a bit…carried away with the whole thing. But it works. The creature landed in paradise and carved out a remarkable little niche. So what if it’s suffered a bit of shrinkage?

Browse the full Absurd Creature of the Week archive here. Know of an animal you want me to write about? Are you a scientist studying a bizarre creature? Email matthew_simon@wired.com or ping me on Twitter at @mrMattSimon.

Reference:

Blair, S. B. (2008) At the lower size limit in snakes: two new species of threadsnakes (Squamata: Leptotyphlopidae: Leptotyphlops) from the Lesser Antilles. Zootaxa 1841: 1–30