Well, That Plan Sucked

Over the course of our long history, we humans have from time to time taken it upon ourselves to designate some animals as pests, and to declare that they must be controlled. Our reasons for wanting to exert our authority over these animals are myriad, but generally boil down to the idea that the animals are either eating or damaging something, and we would prefer that they discontinue doing so.

We have attempted to control pests in a bunch of different ways. One of which is the introduction of predator species, in the hope that they will predate upon our pests and send them packing. It’s an idea that looks good on paper, sounds even better around a conference table, but is all too often disastrous in practice.

Today we are going to take a look at some of these introduced species (sometimes referred to as “biocontrols”) with an eye toward understanding what they were meant to do versus what they actually did.

We’ll begin with one of the most notorious.

Cane Toad (Rhinella marina)

(Cane Toad, Looking Wistful)

Also known as the bufo toad, this poisonous nightmare of an amphibian is native to South America, but was introduced to Australia and the US (specifically Hawaii and Florida) as a method of pest control. The pest in question was the cane beetle, a medium-sized bug that noshes on – wait for it – sugarcane.

But here’s the problem. Cane beetles inhabit the top couple of feet of a sugarcane stalk and cane toads live on the ground. Sugarcane stalks are about 12 feet tall while cane toads can barely jump 18 inches. So, cane beetles and cane toads almost never met face-to-face, and the grand plan that imagined the toads snacking on the beetles never came to pass.

What did come to pass, however, was that the cane toads, being hungry and carnivorous, went ahead and got busy finding dinner anyway. They ate (and continue to eat) insects, sure, but other animals on their daily bill of fare include lizards, other toads, frogs, small snakes, small birds, the eggs and young of all of the above, and pretty much anything else they come across that will fit in their mouths. And they have big mouths.

(Cane Toad, Explaining Why This is HIS Puddle)

The officials who introduced the cane toads saw what beasts were up to, but told people that they needn’t worry. “People,” they said. “You needn’t worry. There are plenty of larger predators around to deal with the toads. Things look somewhat bleak now, it is true, but everything will be wrapped up lickety-split. Go on about your business.”

That’s when another problem sprang up. Or at least seemed to spring up, because surely the well intentioned mullet-heads in charge of the toad project were aware ahead of time that cane toads are toxic. Like way toxic. Like the sort of toxic that kills almost anything that ingests it.

Cane toads have special glands (called parotoid glands) above their shoulders that are positively brim-full with slick, milky-white bufotoxin. The stuff is so poisonous that the Choco Indians of Central America used to dip their arrowheads in the stuff to make them extra deadly. But wait, there’s more! The little buggers are poisonous at every point in their lifecycle, from tadpole to adult toad. Even their freakin’ eggs are toxic. People often lose family pets to bufotoxin, and there have been recorded cases of toddlers and even adult humans dying from the poison.

(Cane Toad, Dripping Bufotoxin)

Long story short, cane beetles are still here, native species that haven’t had enough time to adapt to cane toads are disappearing by the mouthful, and cane toads continue to reproduce to the tune of 25,000 or more eggs per clutch. And in Australia alone, where 135 cane toads were released in 1935, there are now an estimated 1.5 billion of them hopping about.

(Cane Toads, Doing What We Wish They Wouldn't)

If you are a small endangered species, or you know, a large non-endangered person, in northern Australia or Florida, keep your eyes peeled for those lumpish brown toads. You’ll see them coming. The biggest one ever recorded weighed more than five pounds.

Rosy Wolfsnail (Euglandina rosea)

(Rosy Wolfsnail)

Real quick, sit down and put together a mental list of dangerous invasives. Did your list have a snail on it? Probably not, because, I mean, snails? Sure, the slimy little things with their houses on their backs are capable of screwing up your garden or grandma’s flower bed, but can a snail actually harm an entire ecosystem?

Yes. Snails can harm entire ecosystems. Particularly the rosy wolfsnail, also known as the “cannibal” snail.

These menacing predatory mollusks are native to the southeastern United States. They are, insofar as the general run of snails is concerned, enormous. Their shells can be three inches long and nearly two inches up and down. Viewed as they are, in situ as it were, as they snail about in the undergrowth, rosy wolfsnails are actually quite pretty. Those big fusiform shells of theirs are colored in lovely shades of pink and spiral into delicate points front and back. Their shells are also so thin as to be nearly transparent. If you look closely you can see the snail’s body wiggling around in there, which is pretty cool.

(Wolfsnail, On It's Way To Do Something Ghastly)

Once you turn your attention to their mouthparts and their methods of predation, however, rosy wolfsnails get lots less pretty and way more creepy. They have evolved to specialize in eating other snails, hence the “cannibal snail” thing, and they do so with relentless, somewhat gruesome, vim.

Using their lips, which they can elongate something like tentacles, they follow the mucous trails of their intended prey, and because they are one of the true speed demons of snaildom, it is usually a short chase. Once they have captured their unlucky victim, they pin it down and extend their specialized radula (think of a radula as something akin to a tongue dressed in plate mail) directly inside the creature’s shell. (Check out this video.)

The radula has inbuilt utensils in the form of both a beak and teeth, which the wolfsnail uses to slice and dice its victim’s body into a slurry, before slurping it down the ol’ gullet like someone sucking Jell-O through a straw. Unless, of course, the snack-snail is on the tiny side, in which case it is simply swallowed whole.

(Rosy Wolfsnail, Eating. Note the White Radula)

Rosy wolfsnails were introduced to the islands of Hawaii in 1955 to tackle the giant African snail (Achatina fulica, Bowdich), which itself was an introduced species. (Jesus...) The giant snails had been shipped over from Africa in 1936, because people thought they made handsome garden decorations. They were that, I suppose, but then they ran amok. Rosy wolfsnails performed exactly as hoped, devouring other snails by the bowlful. Unless one of those snails was a giant African snail, in which case it was ignored entirely. The cannibal snails wouldn't eat the snails they were meant to cannibalize.

But, yes, the insatiable wolfsnails ate every other species of snail found on the islands, including – tragically – the Hawaiian tree snail (Achatinella apexfulva), a creature that was unable to adapt to the speed and ferocity presented by the new predator in its midst. The tree-snail buffet went on unabated until New Year’s Day of 2019, when the last known member of the species died in the hutch where it had been born, at the University of Hawaii at Mānoa.

(Hawaiian Tree Snail)

In the predictable, lamentable way of biocontrols gone sideways, the rosy wolfsnail hitched rides on boats and planes, and quickly invaded at least 25 other countries – including American Samoa, the Solomon Islands, Papua New Guinea, Japan, Taiwan, Madagascar, the Seychelles, Mauritius, India, Sri Lanka, the Bahamas and Bermuda – where they continue to cause terrible disruptions to local ecosystems.

Okay, So Now What?

It is an unfortunate reality that invasive or hastily introduced species are very difficult to get rid of, once they have established a foothold in a new environment. No matter what people say, targeted eradication programs almost always end up killing species that we were better off having around.

Answers are hard, but we can't just give up.