We know we have an "arachnid response" for things that are horrifying because of their fundamental alien-ness. We don't have a "giant water bug" response because everyone who's seen one is too busy looking for a heavy object and regretting not writing a will. And don't relax thinking that the giant water bugs restrict themselves to smaller prey, either. They've been seen eating things as large as snakes or even turtles, using their horror-monster face to inject flesh-dissolving horrorgoo. They've also attacked humans, and while they don't succeed in their plan to dissolve us like the Blob and slurp up the remains, the fact is that THAT IS THEIR PLAN. But instead of phase-changing us into supper, their uniquely awful poisons "only" cause hours of burning pain as bits of your body turn into flesh-smoothie.

The Japanese Ministry of the Environment lists it as endangered and is concerned about its survival. Come on, Japan, you murder whales as a snack and bulk-eat entire genii of fish, and THIS is the species you decide to keep around? Finish it off before the next nuclear accident gives it the gift of Godzillification!

How We Finish Them Off:

Pacific Rim. Jaegers. Giant hundred-meter-tall multi-weapon-enabled megabots to stamp them back into an organic slurry before they can infest our cities.

But if we have to fight them after they've been irradiated, build a Death Star.

You bet your ass it frolics. The saiga antelope is a sexually overloaded frolicking fuck-machine. The saiga is the evolutionary anti-panda, a species that quite literally screws itself over. The males don't just fight for hump-rights; the winners then hump a whole harem so hard, they often forget to even eat. Male saiga commonly copulate themselves into a post-coital corpse. They're actual, factual deadbeat dads.

After mating season, the survivors then let their hard-won harems disperse, presumably because they just don't want to get tied down, man. So for the privilege of spending a shitty winter alone, the dudes then have to go through the whole horrific round of antler-combat all over again.

Omontero/Pixabay
"Sword fighting each other in the head with your own bones is a great idea." -- Evolution

But saiga aren't built like bee drones with expendable idiot males. They can't afford to throw away healthy adults every mating season. This is an entire species of guys deciding that balls-exploding alpha maleness is so important, they're killing themselves and their species. Even wolves don't subscribe to the alpha male idiocy, and wolves are where scientists first invented that idea. And later retracted it as -- and we paraphrase -- "pretty fucking stupid."

The saigas' "extinction by bro-culture" is made worse by the high mortality of male saiga calves. They simply stink so much of maleness that predators can find and eat them. This is a branch of the evolutionary tree being cut down by the Axe Effect.

How We Finish Them Off:

The saiga are self-exterminating through desperation to prove themselves manly men by jack-hammering their genitals into mulch. If we invent Saiga-Viagra, not only will they wipe themselves out, but no nature documentary could make any sad films about them without an R-rating.

The big-headed turtle looks like it's trying to commit suicide by Mario. It's named after an attribute we consider negative even in humans. Even in Latin it's Platysternon megacephalum, and that's the closest this dumbass design comes to sounding intelligent. But the turtle doesn't even know that, because it's a cranial cargo cult. It's accidentally copying our super-sized skull system in shape alone. It's not any smarter than other turtles. In fact, because its head is too large to retract into its shell, it's definitively dumber than every other turtle.

Wikimedia Commons
"I KNOW, OK? I can't even shrug about this bullshit."

You know you've screwed up pretty bad when your body would fail a Darwinian IQ test. Then again, if Darwin had seen this thing, he'd have torn up his notes and said, "There must be some God out there doing this for a laugh, and he's an asshole." Like many big-headed beings, this total fuckup is incapable of comprehending that its only defining feature is a magnificent mistake. The whole point of turtles is putting all their survival eggs in one basket, which they grow out of bone and hide their entire body inside. Turtles have one survival strategy, and this ignored it. This isn't evolution; it's a fable, a morality tale to teach children to be humble.

How We Finish Them Off:

Headshots! This turtle is the living equivalent of a zombie: slow, stupid, and a great big head weak point it hasn't the smarts to protect. This isn't a species; this is an end-of-level boss for natural selection, which is already removing it from the gene pool. Sure, humanity is helping a bit too much, but we're just another species exploiting a mistake it already made.

A worse problem is that the scrotum frog proves we don't give a shit about things that aren't cute. In fact, it reverses the idea, being exterminated extra-hard because of its horrific appearance. But not out of fear. The poor Titicacan testicle pouch isn't so much a species as an organic satire of human stupidity, physically embodying the absolute worst things that should instead be extinct. Because it's being killed for hard-ons.

The scrotum frog is used in a "frog juice" potion alleged to improve erections. We're not talking about using some rare venom from a scent gland under the expanded folds of its armpit. The ancient, herbal, traditional, and other words that mean "bullshit" recipe involves a few herbs and an entire liquidized frog. What's worse, research indicates that one of the entirely non-endangered plants included in the mix is the thing most likely responsible for any tenuous boner benefits.

Denver Zoo
"Yes, I look like a Hutt after a diet."

Which doesn't stop limp-dicked dudes from chugging frog-shots to get their dicks hard. In the year 2016. And you know many of those involved are still at the stupid/sympathetic/magic stage of "It's called/looks like a scrotum, it's gotta work, and I am prepared to pay to eradicate another species for even the chance of one more erection."

How We Finish Them Off:

Obviously, the best way to defeat a scrotum is by kicking it. And just to be sure, let's field-goal the balls of every asshole dude who drank one as well, so no atoms survive with a hope of reproduction. It's not like we'll break anything.

These ill-fated fungi include some of those horrible "rust" species you see on plants. You know, where you see a lush and thriving green thing, then there's a bulging and crusty red rot eating them from the inside out, like there's a traffic light for life and love and this bastard is red incarnate. Action movies set up the worst villains by having them target innocent bystanders. Rust fungi have genetically engineered themselves over millennia to target green plants, which do nothing but create life from sunlight without bothering anyone. Even in the scientific paper on this fungus's plight, every single image looks like the alien villain in a science fiction movie.

doi: 10.1371/journal.pone.0147895
Seeing this on the viewscreen would make Captain Kirk press the self-destruct button.

They are genuine murderous spores out to corrupt and rot their target. Feeling sorry for them would be like feeling sorry for Xenomorphs finding themselves in a galaxy of Daleks. If your only host is endangered and you keep parasitically eating it, you are karmically incapable of earning sympathy. You went up to natural selection and said, "Don't worry, I'll show myself out."

doi: 10.1371/journal.pone.0147895
A microscopic middle finger to all life.

How We Finish Them Off:

I'm afraid we'd have to work extraordinarily hard to avoid this dying off along with the poor tree. If we absolutely have to take it out quicker, we should probably flash those images on a screen in front of Jeff Goldblum. He'll spend the next hour hacking into trees with his laptop to eliminate them. Just tell him to say "fungi are like a virus." Which is ludicrously wrong, but if his laptop can connect to alien motherships, Earth trees should be no problem.