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This Wasp Turns Spiders Into Zombie Construction Workers

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In another post, we were talking about what happens to spiders and their webs when scientists give them a little bit of marijuana and other drugs. While researching that post, I learned that it's not just humans that alter spiders’ behavior with chemicals. There’s a wasp in Costa Rica that does the same thing, in a more gruesome and sinister way, as part of its journey to adulthood. 

The tropical wasp species Hymenoepimecis argyraphaga is a parasite, and it takes advantage of an unlikely host. The web of the orb weaver spider Plesiometa argyra is normally a place where bugs meet their untimely death and become spider snacks. Using an arsenal of toxins and mind-altering chemicals, though, H. argyraphaga is able to turn the spider into a slave and a meal, and its web into a safe haven.  

When the female wasp is ready to lay her egg, she seeks out a spider to help raise her child. She stings the spider to paralyze it and then lays an egg on its abdomen. Soon, the egg hatches and the larva that emerges remains attached to the spider, living on its abdomen and sucking hemolymph (kind of the arthropod version of blood) from its body for nourishment. After a few weeks like this, during which the spider goes about its life as normal, the wasp larva is ready to move on to the next stage of its life cycle. To do this, it needs to make a cocoon. A spider’s web is a decent place to build one, but not perfect. It’s suspended above the ground and the sticky threads provide defense from predators that might eat the wasp, but it’s far too flimsy to support the heavy cocoon and the adult wasp that will come out of it. 

The wasp gets around this problem by forcing the spider to build a web that suits its needs. It injects a chemical (which hasn’t been identified yet) into the spider that alters the host’s behavior. The spider begins building its web as normal, but instead of completing all the steps and getting a carefully-patterned web, the zombified spider simply repeats the first few steps over and over again, resulting in a web that’s just a few heavily-reinforced anchor threads and a small center section. 

Once the web is done, the spider crawls to the center of the web and sits there complacently. The larva molts, kills the only companion it has ever known, sucks any remaining useful bits out from its corpse, and discards it. Then, it builds its cocoon on a web custom-built for the job. A few weeks later, the adult wasp emerges and flies away, and the cycle starts over. 

For more on parasitic wasps, see any of Carl Zimmer’s paeans to the Emerald Cockroach Wasp. 

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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.

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