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Go to Brilliant.org/SciShow to check  out their course on Scientific Thinking. [♪ INTRO] As strange as it seems, animals  fall from the sky sometimes. Even ones that don’t belong there in  the first place, from fish to spiders.

These phenomena have been known  for centuries, but in many cases we still don’t know where the  heck all these animals came from. But answering that question begs another one. Because we don’t always know what happens to them.

I mean, yes, splat. But actually a lot more than just splat. In some cases, animals can actually  benefit from their aerial adventures.

While these animal rainstorms  can in fact be deadly, sometimes animals are adapted to be rain. So let’s look at five of the potential  outcomes for animals that become rain, whether they mean to or not. We’ll go ahead and get the  “splat” out of the way first.

It’s often a bit murky exactly  how fish and frogs end up on land and far from their home waters. But there have been enough instances  of weird rains of aquatic creatures for a lot of hypotheses to  begin circulating around. Some have speculated they were  lifted out of their ponds and streams by waterspouts, or maybe that  torrential rains flushed the animals from underground, and they didn’t  actually fall from the sky at all.

Regardless of how they got  there, you can imagine that after being caught stranded on land,  fish are not gonna fare too well. And even if they did happen to land in  a new and ideal aquatic environment, they might have already been exposed  to less-than-ideal conditions during their travel, like getting too cold or dry. But it’s not just aquatic animals  that rain down from the sky.

There are accounts of huge  numbers of birds that have dropped dramatically from above,  already dead or injured from unfortunate events like extreme  weather or forest fire smoke. But sometimes there’s actually  a strategy to their swift and dangerous descent to Earth. In early 2022, hundreds of  yellow-headed blackbirds rained down on the city of Cuauhtémoc, Mexico.

Video footage of the bizarre incident  showed a massive and tight black cloud of birds rapidly drop down to the street. While hundreds immediately flew back  up towards the sky, many of them died when they collided with the  road and surrounding infrastructure. This isn’t the only case of flocks of  birds seemingly dropping out of nowhere.

It typically happens to birds who hang  out in large flocks, like starlings. Many causes for these unfortunate  events have been speculated, ranging from air pollution to 5G technology. Far more likely than that, however,  is that this is the result of a calculated risk gone wrong as the birds  dove for cover from an aerial predator.

There are a number of bird species that attempt to escape predation in a coordinated manner. They fly in a tight group, swiftly  changing direction and altitude in what appears to be a single unit. This generally works quite well, since  predators don’t seem to like diving right into the cloud, and instead try to  pick off birds that stray from the group.

In a last ditch effort, birds might dive very low towards the ground to avoid being caught. If the group takes a deep dive and is  forced too low, say into a building or pavement, the coordinated  maneuver becomes catastrophic. While this may result in a fatal collision, sometimes desperate times  call for desperate measures.

Now, speaking of collisions, one  type of animal rain might just result in a very large reptile  bonking you on the head. Thanks to its balmy climate, and a  fair bit of carelessness on our part, in the United States, Florida is home to many introduced species of the reptilian variety. Whether from accidental  introductions by tropical cargo or purposeful releases of exotic pets,  some of the over 150 documented reptile introductions have reached  invasive population levels, including one very large lizard.

The native range of the green iguana  includes Mexico south to Paraguay and Brazil, but they’ve  been kicking around Florida since at least the 1960s thanks to the pet trade. Now, much of central and southern  Florida is warm enough year-round for these heat-loving lizards, and luckily  for them cold snaps are pretty rare. But when they do happen they can put  iguanas and innocent pedestrians at risk.

If the temperature drops too  low during a Florida winter, iguanas have been found to  literally fall from the trees. Now, iguanas do sometimes purposely  drop from tree branches to avoid danger, but that’s not what’s happening in these cases. Iguanas are exothermic, meaning they rely on external temperature to  maintain their body temperature.

They’re usually most active  above 25 degrees Celsius, so lower temperatures can  slow them down considerably. And during these cold snaps, temperatures dip as far as zero Celsius, a considerable drop. This can immobilize the iguanas to the point where they’re just no longer able  to hang on to their perch.

And as you can imagine, getting  struck from above by a stiff, six-foot-long lizard is not  going to feel very good. So in these cases, there have even been official ‘falling iguana’ alerts issued to residents! Thankfully, as long as they weren’t injured  in the process, these grounded iguanas can wander their way back up into their  trees once things warm up a little.

And much like iguanas, certain  ants make their homes in trees, including many species in  Central and South America that spend their entire lives way  up in the rainforest canopies. These arboreal ants are well adapted  to life high up in the canopy, with special sticky feet that help them cling  to their home tree at startling heights. Even so, they do occasionally lose their grip and take a tumble if they become  dislodged or are startled.

But even in these cases where  it does start raining ants, you don’t have to worry about  them landing in your hair while you walk by some 30 meters below. That’s because they’re very good at  gliding their way back to their home trunk. The dramatic descents of  one species in particular, Cephalotes atratus, has  been quite well documented.

In a study published in Nature in 2005,  researchers used video recordings and field experiments to determine  that these falling ants hit their home-trunk target  more than 80% of the time! Building on this, later studies manipulated  the legs and abdomens of these ants to figure out how they were able to  maneuver themselves home so accurately. They adjust their body’s  position while in rapid freefall, spinning around to align their  abdomens towards their home trunk before gliding over to it,  their rear end leading the way!

While it does appear to be a whole-body effort, their hind legs seem to play an  especially key role in their ability to redirect themselves towards their  home tree during these big falls. But it’s not just this one species who  can glide their way back to safety. This directed aerial descent has actually evolved numerous times within different ant subfamilies.

And though they don’t all  glide in the exact same manner, this proves to be a vital  adaptation to arboreal ants. If they weren’t able to  latch back onto their tree, they would fall the human equivalent  of 5 kilometers from their home, and into dangerous, uncharted territory. And if falling ants make you squirm,  you might not want to imagine numerous tiny spiders raining  down after flying through the sky.

But imagine a bunch of teeny tiny  baby spiders climbing to a high point, letting out strands of silk, and  floating off into the distance, sometimes hundreds of kilometers away. This ballooning behavior is found all over  the world in different spider species, and it’s often no short flight. Some spiderlings have been found as  high as four kilometers up in the sky!

And we’ve actually been pondering  this behavior since the early 1800s. Even Charles Darwin puzzled  over ballooning spiders that landed on the Beagle while  they were out in the ocean! Over the years there have been two main  hypotheses regarding airborne spiders.

Some thought it was simply the wind  carrying them to far off places, while others thought that it was  electrostatic forces in the atmosphere. And while the wind would seem  to be the obvious choice, it doesn’t fully explain why spiders  choose to balloon on calm days. Plus the multiple silk strands released  for their flight splay out like a fan, and don't tangle in the wind as you might expect.

A study published in Current  Biology in 2018 finally tested the electrostatic  theory for the first time. And they found that while these  little spiders likely rely on a combination of the two factors, the  electrostatic forces played a major role. To test this, they generated a  controlled electric field in conditions without any moving air, and  introduced some baby spiders.

The spiders readied themselves and took off! Using the electric field, the  researchers were even able to control the altitudes of the  spiders once they were in the air. They also found that little hairs  on their exoskeleton respond to changes in the electric field around them,  likely signaling to them it’s time to fly.

Of course, these spiders aren’t  just flying for the fun of it. This ballooning behavior allows these  wingless flyers to find new habitats, which would otherwise be too far to crawl to. That way, they can avoid overcrowding  and food availability issues that might crop up if they  all stayed in close proximity.

So, maybe not all reports of  animal rains are legitimate. After all, we humans tend to tell tall tales. But in other cases, the observations  are not only well documented, but are often happening for a very good reason!

And while some cases of animal rain can  be deadly for the poor falling creatures, other times they not only survive their  aerial drops, but might even benefit from it. Looking at strange things like  animals falling from the sky and searching for explanations  is just what scientists do. And if you’re looking to train your  brain in that kind of rational approach, you might like Brilliant’s  course on Scientific Thinking.

There, you'll dispense with  number-crunching and mathematics in search of something more  useful: physical insight. This is just one of their  many courses recently upgraded to make it even more interactive than before. They’re designed to engage your  curiosity, not ask you to memorize stuff.

And don’t worry if you’re busy. Their courses are split into bite-sized  pieces so you can learn at your own pace. Brilliant has a ton of science,  engineering, and computer science courses, so you can always find something new to learn.

To get started, head to brilliant.org/scishow to save 20% on an annual premium  subscription to Brilliant. [♪ OUTRO]