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Plenty of animals migrate, moving from place to place in search of food, warmer weather, or safe places to reproduce. And lots of animals pull  off incredibly long treks .

But the animals we’re going to talk about today, while they don’t take the longest trips ever,   go farther relative to their body  size than just about anything else. They’re all under about 10 centimeters in size, and they pull off some seriously  impressive long distance travel. And they’ve got some tricks up  their sleeves to make it happen.

Up first, ruby-throated hummingbirds. Ruby-throated hummingbirds migrate from  the southern United States to Mexico -- a trip that puts the Gulf of  Mexico squarely between them and a winter home filled with flowers to dine on. But these birds only have a  body size of 8 centimeters, so the 800-kilometer trip is 10  million times their body length!

If a human of average height,  about 170 centimeters tall, were to travel that kind of relative distance, it would be equivalent to  traveling 17,000 kilometers. Which would be like walking from the  northern to the southern tip of Africa -- and back again. For the hummingbirds, this is a non-stop flight.

There’s nowhere for them to take a layover. Because while they could travel around the Gulf,  they opt for the shorter direct trip instead. It takes them nearly 20  hours of non-stop flying -- and they burn up nearly half  their body weight in fuel.

Small birds tend to have high metabolic rates,  and hummingbirds run some of the highest. Under   normal circumstances, if a hummingbird can’t  find enough food and calories during the day,   they risk starving overnight. So to prepare for their  snack-free 20-hour marathon, ruby-throated hummingbirds pack on  as much extra energy as they can, increasing their body weight until their  body composition is nearly 40% fat.

Which is a lot. Other animals that have that much  body fat include whales and seals, whose insulating blubber keeps them warm, and  hibernating bears who are inactive for months -- not hours. Technically, this isn’t even the longest  migration undertaken by hummingbirds.

The rufous hummingbird migrates from Mexico to  Canada along the west coast of North America. That trip averages 6400 kilometers -- or 80 million times their body length -- but flying over land means they have  chances to stop for food and rest. Now hoverflies -- a group of flies that  superficially resemble bees -- don’t migrate as far as the hummingbirds.

But their tiny size makes the scale of  their migration all the more impressive. Hoverflies migrate across the English  Channel between the UK and mainland Europe. At its shortest, that’s a  distance of about 250 kilometers.

Which might not sound like too far,  but for a centimeter-long insect, that distance is 25 million  times their body length. For our average human, that would  be like traveling 42,500 kilometers, or a full lap around the Earth and  change -- just to get some food! In the spring and fall, between 1 and 4 billion  hoverflies make this seasonal roundtrip.

Now they’re not the strongest fliers. And near ground level, the winds are blowing the  wrong direction to assist them in their journey. And this happens in both directions -- the winds change with the seasons,  which just seems a little unfair.

But by flying up at least 150  meters into the atmosphere -- and occasionally as high as 750 meters -- hoverflies tap into tailwinds that  blow them in the right direction. And being so tiny, they can save energy  and just let the wind carry them. This trick of using high altitude air currents  is actually pretty common in migratory insects.

But it wasn’t until advances in  radar in the 1970s that scientists were really able to track them as  they moved through the atmosphere. That’s when we learned that  a lot of insects migrate -- and have a serious ecological impact.  And we pretty much had no idea. In fact, these international hoverfly travelers  are incredibly important for pollinating crops   in the UK, where they spend the summer.

They  also eat up pesky aphids, protecting the plants. And video footage from 2017 detected migratory  hoverflies in North America as well, where they’re   likely also providing this important agricultural  service as they travel along the West Coast. Now monarch butterflies, with their yearly trek across the US to their  overwintering sites in Mexico, might be the most well-known migratory insects.

Depending on where in North  America they start out, the migration south can be nearly 4800 kilometers. Given that the butterflies are  only about 3.5 centimeters long, that distance is 135 million  times their body length. That’s like our average human  traveling 229,500 kilometers -- equivalent to going around the  Earth over five and a half times.

Now, not all North American monarchs migrate. Those that live in the warm southeastern  US, for example, stay put all year. But the migratory monarchs have  quite the challenge ahead of them.

Like hoverflies, monarchs take advantage  of air currents to save energy as they fly. But traveling across nearly an entire  continent requires some navigation skills, too. And researchers believe that monarch  butterflies make use of not one but two internal compass  mechanisms to orient themselves.

The first one uses the Sun. While traveling, monarchs monitor the position   of the Sun in the sky as it rises  in the east and sets in the west. If they are headed south, they must keep  the Sun on their left in the morning, but on their right in the afternoon.

And the butterfly’s biological  clock helps to compensate for   the sunrise-to-sunset shift  in the position of the Sun, and tells the insect which direction is which. Light cues from both their eyes   and their antennae are crucial for this  clock-compass combo to work properly. The second compass likely  acts as a backup in cases where the weather is overcast and the  butterflies can’t rely on sunlight.

This one is a magnetic compass, like the one that’s been observed in some birds. Basically, they can detect differences  in the angle of Earth’s magnetic   field as they travel from north to  south, again using their antennae, and orient themselves in the right direction. And they can use it to point  them either north or south.

Which is important, most migratory insects simply don’t  live long enough to make a two-way trip -- a different generation goes back the other way. But some monarchs are actually tough enough  to make the full round trip migration -- so they need the tools to get home again. Now for a somewhat less charismatic insect,  but one that’s just as great a traveler.

The desert locust is a notorious pest, one  whose massive swarms can devastate crops. Under normal circumstances, the desert  locust is just another grasshopper. But when their numbers get crowded, their  behavior switches to traveling swarm-mode.

They can regularly travel 5000 kilometers  across Africa and parts of the Middle East, and they’ve even crossed the Atlantic Ocean -- a distance of some 10,000 kilometers, and a trip that wrecked fields in the  Caribbean and South America in 1988. For these grasshoppers, which  are about 7 centimeters long, their travel distance can be anywhere from  about 70 to 140 million times their body size. For a human, this would be comparable to  traveling 238,000 kilometers at the longest.

That’ll get you more than halfway to the Moon. Even when they aren’t accidentally picked  up by strong Atlantic-spanning winds, locust swarms typically make use of air currents  to quickly cover thousands of kilometers. When they have to do the flying themselves,  though, they load up on carbohydrate-rich foods, much like a human endurance athlete would.

Locusts store the carbohydrates  as energy-rich glycogen and burn this fuel to power their wing muscles. And this is precisely why locust plagues  can be so devastating for farmers: our favorite crops, like wheat  and corn, are carb goldmines. Add the fact that an adult locust can  easily eat its weight in food daily, multiply that by a few tens of millions of locusts  per swarm, and you’ve got a recipe for disaster.

Our last tiny record holder  really lives up to its name. The wandering glider, also called the  globe wanderer, is a species of dragonfly that is found all over the world --  on every continent except Antarctica. In 2012, researchers discovered  that wandering gliders they found on the eastern coast of Africa  had arrived there from northern India.

The little dragonflies would have  had to have crossed the Arabian Sea, and possibly the Himalayas,  to reach the African shores. That’s a distance of 16,000 kilometers,  or a whopping 320 million times its 5-centimeter body length. And a good  portion of that distance is over open water.

If a human were to travel that kind of distance,  it would be equivalent to 544,000 kilometers. So you’d walk not just to the  Moon, but halfway back, as well. Like many of our tiny migrants, these  dragonflies use wind to travel efficiently.

The wandering glider has relatively  large wings to help it glide, and it makes use of air currents higher  than 1000 meters up in the atmosphere,   much higher than the hoverflies. Many species tend to live in separate  populations across their range, not always interacting with  members of other populations. But researchers think there is only  one population of wandering gliders.

A 2016 study found pretty regular  gene flow occurring between   all the different locations  where the gliders are found, suggesting they’re traveling far enough to mate  with one another pretty much wherever they live. So the researchers proposed that  the species is best considered   to be a single population of  globally mingling individuals. Unlike the round-tripping monarchs, though, a single wandering glider can’t pull  off a complete tour of the globe.

Successive generations each  travel a leg of the journey, so you can think of this worldwide   population as participating in a  continent-spanning relay race -- with no defined finish line. Now, most migrating animals  do so in order to find food, or to find breeding grounds full  of food for their offspring. This makes most migrations seasonal.

Wandering gliders require  freshwater pools to breed, so their migration tracks rainfall. Rainfall does vary seasonally, but instead of  the there-and-back-again of migration patterns, these dragonflies have taken to wandering. They follow those high-altitude wind currents -- even across oceans -- and snack on tiny airborne organisms while  they glide wherever the wind takes them.

But because insects are small and short-lived,   it’s still tricky to track the  movements of a single individual. Scientists haven’t yet been able to figure out  all the wandering gliders’ migratory paths, so there’s probably more we don’t know yet. So the next time you think it’s  a long way to the grocery store, just remember these globe-trotting creatures.

At least no one’s asking you  to walk to the Moon and back! Thank you for watching this episode of SciShow, and thank you to our patrons  for helping to make it happen. We appreciate you guys just as much as  if you had walked to the Moon and back.

If you’d like to get involved and  help us make free videos for everyone, check out patreon.com/scishow. [ outro ].