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This Assassin Only Kills If Its Victim Strikes First

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Letting your opponent land the first blow usually isn’t a surefire strategy for winning a fight, but for one insect predator, it’s the only way to come out on top.

As their name might suggest, assassin bugs are formidable killers. They’ve got a long proboscis that they use to stab prey, inject a tissue-liquefying toxic saliva and suck the pre-digested innards out for consumption. It’s like a harpoon, syringe, and straw all in one. 

When brute strength and poison aren’t enough to make the kill or get out of trouble with their own predators, the bugs have a few other tricks. One species wears its victims’ flesh as a disguise. When it’s finished with its meals, the assassin tosses the drained carcasses onto its sticky back, building a cloak of corpses that disguises the bug and protects it from spiders. 

Another species hunts spiders instead of hiding from them, and plucks the strands of their webs to mimic the vibrations of struggling prey. When the spider rushes over expecting a meal—Pow! Toxic proboscis sneak attack!—it becomes one instead. 

Scientists have just discovered a different sort of tactic used by the species Ptilocnemus lemur, which hunts ants. It also deceives its quarry, but uses one of its own legs as a lure and lets an ant attack it before going in for the kill.

The assassin bug begins by waving one of its bristly hind legs around to attract nearby ants. Unlike all the other lurer hunters that the researchers know of, the assassin doesn’t strike when an ant gets within range, or even when it touches or grasps the bait. It just waits.

Finally, when—and only when—the ant firmly grips the bug’s leg and either attempts to sting it or drag it away, the assassin leaps into action. With the ant still hanging on to its leg, P. lemur lifts itself up and swivels 180 degrees on its “knee” joint. Now its body is above the ant, and perfectly positioned to attack a weak point in the prey’s hardened exoskeleton—a soft membrane between the head and thorax. 

Proboscis goes in. Nutritious goo comes out. 

As the researchers, led by Australian ecologist Matthew Bulbert, watched, the assassins successfully killed 81 percent of the ants that fell for their trick. In almost 500 of these attacks, though, not one assassin bug died. 

Ants are dangerous game and adept insect killers themselves. Some species are also several times bigger than the assassin bugs. Using its own leg as bait with them would seem to put the assassin in harm’s way, but Bulbert and his team think the seemingly risky strategy of letting the ant bite first actually reduces the bug's chances of getting hurt. 

By presenting its leg and waiting until the ant latches on, the assassin has tricked the ant into concentrating all its offensive traits—its size, its jaws and its venom—onto one body part. Once the ant attempts to claim its meal, its entire arsenal is occupied, and it's unable to defend itself from an quick counter-attack that comes from above and behind its head. By taking a blow to the leg, the assassin bug turns the hunter into the hunted “unopposed and essentially risk free,” the researchers say. 

Crafty and effective as it is, the strategy also has some constraints. Only 2.5 percent of the ants that the researchers saw actually grabbed the assassin bugs’ legs. But the slim chance of an ant falling for the trick, Bulbert thinks, is offset by their size. The average ant that the assassins preyed on was one to two times larger than its killers, and could feasibly provide enough food to keep an assassin going through some lean times. In some cases, the ants were as much as five times bigger than the assassin, and the bug lost all contact with the ground when it flipped over on top of its prey and had to ride on the ant’s back until it died. 

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Animals
Watch as Hummingbirds Fly, Drink, and Flap Their Tiny Wings in Slow Motion
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Hummingbirds have more feathers per inch than nearly any other bird, but it’s hard to fully appreciate their luminescent colors when they beat their wings between 70 to 200 times per second.

For the enjoyment of birders everywhere, National Geographic photographer Anand Varma teamed up with bird biologists and used a high-speed, high-resolution camera to capture the tiny creatures in slow motion as they flew through wind tunnels, drank artificial nectar from a glass vessel, and shook water from their magnificent plumage.

[h/t The Kid Should See This]

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Big Questions
Why Do Dogs Howl at Sirens?
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A dog's behavior can often prove confusing to their human colleagues. We know they like to eat their own poop, but puzzle at their motivations. We're surprised when dogs give a ladybug the same greeting as a home intruder.

Topping the list of eccentric canine behavior: Why do dogs howl at sirens? Is there some genetic predisposition to responding to a high-pitched alarm from passing ambulances or police vehicles?

As it turns out, the reason dogs howl at sirens is because of their ancestry—namely, the wolf. When members of a pack are fractured and spread out, their companions will howl to provide a way of locating them. Think of it as nature’s GPS: By howling, dogs are able to communicate their respective locations to one another, even across long distances.

Since dogs really don’t know what a cop car is supposed to sound like, they’ll often interpret a siren as an animal’s howl. It’s also possible that dogs consider sirens to be a sign that something is abnormal in their environment, and that they want you, the pack leader, to be aware of it.

Contrary to belief, a dog is rarely howling because the noise hurts their delicate ears. If that were the case, some experts say, then they would display other behaviors, like running and hiding.

The more a dog hears and responds to a siren, the more they might be compelled to continue the behavior. That’s because dogs who howl and then notice the sound drifting away might begin to associate their vocalizing with the disappearance of the noise. In the future, they’ll probably recall that they “drove” the interloper away with their warbling and repeat the process.

While howling is usually harmless, sometimes it can be a sign that your pet is feeling separation anxiety from an owner or that they’re feeling unwell. If howling persists even without a screaming siren within earshot, you might consider taking them in for a check-up.

If you’ve wondered why dogs howl at sirens, now you know. It’s simply a way of signaling their location and not because it pains them. Owners, on the other hand, might feel differently.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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