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Animals have evolved a variety of ways to survive—including outright theft.

Hosted by: Michael Aranda

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Sources:
Dewdrop Spiders
http://science.sciencemag.org/content/205/4411/1149
https://pdfs.semanticscholar.org/3c2f/fd8ca9f5e44df19d89b6fd048dd68af794e9.pdf
http://araneae.thu.edu.tw/lib/publications_lib_pdf/1998_Tso_IM__Severinghaus_LL.pdf
https://bioone.org/journals/invertebrate-systematics/volume-28/issue-4/IS14010/Evolution-of-host-use-group-living-and-foraging-behaviours-in/10.1071/IS14010.short
https://www.cambridge.org/core/journals/journal-of-zoology/article/statedependent-prey-t
ype-preferences-of-a-kleptoparasitic-spider-argyrodes-flavescens-araneae-theridiidae/605D4F2B7784D03C654BA2FF803FB474
Fork-tailed Drongos
https://royalsocietypublishing.org/doi/full/10.1098/rspb.2010.1932
http://science.sciencemag.org/content/344/6183/513
Cuckoo bees
http://digitallibrary.amnh.org/bitstream/handle/2246/2902/N3349.pdf?sequence=1
http://digitallibrary.amnh.org/bitstream/handle/2246/5058/N3029.pdf?sequence=1
http://digitallibrary.amnh.org/bitstream/handle/2246/2926/v2/dspace/ingest/pdfSource/nov/N3309.pdf?sequence=1&isAllowed=y
https://academic.oup.com/aesa/advance-article/doi/10.1093/aesa/say031/5115643
https://entomologytoday.org/2018/10/29/cuckoo-bumble-bees-cheating-ways/
Mouth-Diving Snails:
https://www.researchgate.net/publication/238451301_Sneaky_snails_and_wasted_worms_Kleptoparasitism_by_Trichotropis_cancellata_Mollusca_Gastropoda_on_Serpula_columbiana_Annelida_Polychaeta
https://link.springer.com/article/10.1007/s00442-003-1467-1
http://natuurtijdschriften.nl/download?type=document;docid=596852
Plant-robbing Flies
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0153900
https://www.newscientist.com/article/2087352-carnivorous-plant-conned-out-of-a-meal-by-cunning-fly-larvae/
https://www.jstor.org/stable/5718?seq=1#page_scan_tab_contents
Bartering Macaques
https://www.newscientist.com/article/2132748-monkey-mafia-steal-your-stuff-then-sell-it-back-for-a-cracker/
https://rd.springer.com/article/10.1007%2Fs10329-017-0611-1
https://jbleca.webs.com/robbingbartering.htm
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Images:
https://commons.wikimedia.org/wiki/File:Kleptoparasitic_Spider_-_Flickr_-_treegrow_(2).jpg
https://commons.wikimedia.org/wiki/File:Dicrurus_adsimilis-01.jpg
https://commons.wikimedia.org/wiki/File:Cuckoo_bee_(Nomada_sp).jpg
https://www.flickr.com/photos/118037005@N06/23881829480/
https://i420.photobucket.com/albums/pp281/MPassage/Gods%20Pocket%20August%202015/Molluscs%20and%20Others%20from%20BC/20.%20Checkered%20hairy%20snail%20DSC_2416_zps76je9oga.jpg
https://www.flickr.com/photos/118037005@N06/23881829480/
https://www.inaturalist.org/photos/18948294
https://commons.wikimedia.org/wiki/File:%D0%9C%D0%B0%D0%BA%D0%B0%D0%BA-%D0%BA%D1%80%D0%B0%D0%B1%D0%BE%D0%B5%D0%B4_(Macaca_fascicularis)_2.JPG
https://commons.wikimedia.org/wiki/File:Fork-tailed_Drongo,_Dicrurus_adsimilis,_at_Mapungubwe_National_Park,_Limpopo,_South_Africa_(18839328671).jpg
https://commons.wikimedia.org/wiki/File:Meerkat_in_Namibia.jpg
https://commons.wikimedia.org/wiki/File:Sleeping_Melecta_01_(MK).jpg
https://commons.wikimedia.org/wiki/File:Fork-tailed_Drongo,_Dicrurus_adsimilis,_at_Mapungubwe_National_Park,_Limpopo,_South_Africa_(18214043114).jpg
https://www.flickr.com/photos/treegrow/7868013190
https://www.flickr.com/photos/chidorian/3670256482
https://commons.wikimedia.org/wiki/File:Fork-tailed_Drongo_(Dicrurus_adsimilis)_2.jpg
https://en.wikipedia.org/wiki/File:Meerkat_(Suricata_suricatta)_Tswalu.jpg
https://www.flickr.com/photos/dkeats/15585613955/
https://www.flickr.com/photos/berniedup/31655330124
https://www.flickr.com/photos/sumarieslabber/36785164832
https://www.flickr.com/photos/vipinbaliga/14059008450
https://commons.wikimedia.org/wiki/File:Pasites_maculatus,_f,_pakistan,_face_2014-11-02-01.46.02_ZS_PMax_(15786919381).jpg
https://www.inaturalist.org/photos/8711493
https://www.inaturalist.org/photos/29067
https://commons.wikimedia.org/wiki/File:Spiralis_w-Victim_(12558642363).jpg
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0153900
https://www.youtube.com/watch?v=ymYDfHXq4S0
https://www.youtube.com/watch?v=uhqKux-liGk
[INTRO ♪].

Surviving on this planet is tough. That’s why animals have evolved so many diverse adaptations for hunting, gathering, hoarding, and otherwise getting hold of the resources they need for themselves and their families.

But there are also animals that cheat the system. They wait for others to do all that hard work and then just steal their stuff. It’s a strategy called kleptoparasitism, and it’s incredibly common.

If you’ve ever had your French fries stolen by a gull on the beach, you, too, have been the victim of a kleptoparasite! But like in human societies, larceny is a risky choice. If an animal gets caught stealing, the best case scenario is they miss out on dinner.

The worst case is that they become dinner. So, while lots of animals will occasionally steal, relatively few have developed specialized thieving techniques. But those are the ones we’re going to talk about today.

The 6 animals on this list are particularly adept thieves that have evolved special traits which allow them to live a life of crime. Many spiders use webs to catch their prey, and it’s a great system. Not only do they get to sit around and wait for their meals to come to them, they can also use their silk to wrap things up for later.

But there’s a catch: when you leave food around, you might as well be asking for it to be stolen. So spider webs often get plundered, especially by dewdrop spiders. Because who better to steal from a spider than another spider?

These thieves sit around on other spiders’ webs and wait until they sense the tell-tale vibrations of prey being caught and wrapped up in silk. Then, when the host spider isn’t looking, they make their move. Their long legs allowing them crawl stealthily across webs to their free, gift-wrapped meals.

And they’re so successful that there are more than 200 species of dewdrop spider, most of which are kleptoparasites. But research suggests they didn’t start out as thieves. Their sneaky skills likely evolved for murder instead.

Some of their closest cousins are spiders that eat other spiders by sneaking onto their webs. And a 2014 study concluded the ancestors of dewdrop spiders probably did the same thing. They switched to theft around 25 million years ago, which is about the same time that orb-weaver spiders became more diverse and widespread.

More webs meant more opportunity to steal. And since there are a lot of risks that go along with straight-up attacking another spider, the dewdrops could use the stealth they evolved for sneaking up on prey to avoid conflict instead. These days, some species are so dedicated to thievery that they’re basically unable to hunt for themselves.

But they don’t necessarily have to wait for an opportune moment to sneak in for a snack. If they’re feeling impatient, some dewdrops will shake the web to scare the host spider away. They’ve also been seen tearing down parts of their hosts’ webs and straight-up eating the silk.

And sometimes, that ancestral predatory urge strikes, and they kill and eat the host spider or its babies. I guess old habits die hard. Thieving is pretty common in birds.

Shorebirds, like gulls, are especially infamous for bullying each other out of meals. But the fork-tailed drongo of southern Africa takes things to a whole other level. This isn’t just a thief—it’s also a liar.

Most of the time, drongos are happy to hunt for their own food—tasty little critters like lizards or crickets. And they generally get along pretty well with their neighbors, which include meerkats and other birds. In fact, these other species tend to benefit from drongos hanging around because the birds keep a sharp eye out for predators, and sound a loud alarm if they see danger approaching.

But drongos aren’t always so neighborly. They sometimes fly over and harass other animals into giving up their food. But, since direct confrontation can be risky, they’ve learned a more devious strategy: they lie.

A drongo will sometimes make a false alarm call, and then, when a scared animal drops its meal and runs to hide, it pops over and snatches up the food. You’d think the other animals would just stop believing the drongos. After all, that’s what’s supposed to happen when you cry wolf.

But drongos are exceptionally talented, and they can mimic the alarm calls of other species. All in all, they’re able to make more than 50 different calls, almost all of which are impersonations. Though they’re smart birds, scientists suspect they've learned to lie via trial-and-error.

It’s not that they understand what the other animals are thinking and use that to exploit them— they just make alarm calls they’ve heard and keep making ones that work. And having so many voices at their disposal means drongos can mix up their game when their victims do start to catch on. So, their prolific lying pays off—these deceptive birds can get a quarter of their daily food this way.

Most kleptoparasites steal because it saves them the effort of gathering food for themselves. But it also takes a lot of effort to collect food for your young. Take bees, for example.

When it comes time to make babies, many bees put a great deal of energy into building elaborate nests with chambers to house their eggs and collecting food so their larvae will have plenty to eat. But cuckoo bees don’t bother with all that. Instead, they find another bee mama’s nursery, and swoop in when no one’s around to lay their own eggs, much like the similarly-named birds that lay eggs in other birds’ nests.

And cuckoo bees are well adapted for mooching off other, hard-working bees. Adults generally lack the special pollen-collecting bits other bees have, and instead, are fairly well-armored in case of confrontation. Meanwhile, the larvae hatch early and quickly develop tough heads, sensitive antennae, and large, sharp jaws.

These allow them to find and kill the host bee’s babies. Then, they can just sit back and enjoy all the delicious food that’s laid out. It may sound brutal—because it is—but it’s clearly a winning strategy.

This behavior has evolved more than 20 separate times in bees, and biologists estimate as many as 15% of bee species are cuckoo bees. Usually, their victims are solitary bees, but some extreme cuckoo bees target social hives. And the most hardcore ones don’t just drop the eggs off and leave.

They take over the entire colony. No joke: they infiltrate the nest, kill and replace the queen, and force the workers to raise their larvae. Their behavior is so extreme scientists have a whole term for it: social parasitism!

The devious queen eventually leaves, dies, or falls victim to a hive mutiny, but usually not before her scheme has paid off in the form of many bouncing baby bees. For most kleptoparasites, the trick is to get the food after another animal has caught it, but before they’ve actually started eating it. But some ocean-dwelling snails will steal meals right out of other species’ mouths.

The snail Trichotropis cancellata lives in the northeast Pacific Ocean, and it’s normally a suspension feeder that snags plankton from the surrounding water. But sometimes, it gets food directly from its neighbors: tube worms. These tube worms anchor themselves to the seafloor and build a mineralized tube around their body.

When they want to hide away, they can withdraw into their tubes. But when it’s time to eat, they nab plankton from the water with their tentacles. And that means a successful tube worm can be a treasure trove of treats for a hungry snail.

So, once a worm has gathered a bunch of tasty morsels, a snail will crawl up to its head, stick its proboscis-like mouth between the worm’s tentacles and grab food right out of the worm’s mouth. And it turns out the snails are pretty strategic about this. A 2004 study found that the snails generally steal from the worms in autumn when plankton is in short supply.

Not only that, the snails that steal from worms grow up to 18 times faster than the snails that don’t! It’s actually not unusual for suspension feeding snails to supplement their diets by snacking on algae or organic matter off the surfaces they crawl along. So it’s likely these snails kind of stumbled into stealing when they realized their sessile neighbors were slow to digest their meals.

And, believe it or not, the worms apparently don’t fight back, so the snails have a pretty easy time of it, sometimes taking literally all of the worm’s food. Swiping a meal right out of your victim’s mouth might seem like a bold move, but at least one other snail species goes even further. In 1987, a scientist reported witnessing a wentletrap snail in an aquarium steal from an anemone by crawling onto it and sucking food directly out of its stomach.

Kleptoparasitism is almost exclusively something that happens between animals, but some scheming critters have found another target to steal from: plants. Flower flies—which are sometimes called hoverflies—feed on pollen and nectar as adults, but their larvae tend to have a more carnivorous palate. Usually, they go after slow-moving bugs like aphids or other insect larvae.

But in the neotropics, where aphids are rare, Brazilian flower flies had to look for other sources of food. What they found, apparently, were sundew plants. Sundews are carnivorous plants that lure in insects, trap them with sticky mucus, and then slowly digest them with a cocktail of enzymes.

That is, unless a Brazilian flower fly maggot gets in the way. These flies lay their eggs on the sundews, and the larvae that hatch come fully-equipped to burgle the poor plants. The bugs secrete a fluid that prevents them from getting stuck like their meals, and their thick exoskeletons protect them from the plant’s digestive juices.

The flies spend all or most of their larval lives on the sundew, crawling about with impunity and gobbling up the bugs the plant has captured. When the larvae grow up into adults and it comes time to lay their own eggs, they tend to choose large sundews with upright leaves, possibly because they offer more prey and protection for the developing grubs. These flies aren’t the only animals that steal snacks from carnivorous plants.

Other insects are known to do it, as well as at least one species of slug! But in many of those cases, researchers think the plant doesn’t completely lose out because it’s able to absorb nutrients from the thief’s fecal matter. These flies don’t defecate until they’re ready to become adults, and then, they poop where the plant doesn’t have digestive glands.

So as far as researchers can tell, they just straight-up steal without giving anything in return. You may not be surprised to hear that monkeys steal things. After all, our primate cousins are notoriously intelligent and mischievous.

But the long-tailed macaques living on the island of Bali in Indonesia are a special case. Not only have they developed a unique thieving strategy, their victims are humans! The best place to encounter these macaques is at Bali’s Hindu temples, which are popular attractions for traveling humans and hungry monkeys.

Hang around one of these places long enough and you might just get robbed. The macaques commonly steal people’s glasses, hats, shoes, cameras … anything they can get their monkey paws on. But they don’t just take off with the stolen goods because what they stole isn’t actually what they want.

What they want is food, and they’ll hold your stuff hostage until they get it. This behavior is called robbing and bartering. The little monkey mobsters will wait until someone offers them a tasty treat, then happily drop what they stole and run off to enjoy their meal.

This unique form of kleptoparasitism was examined closely in a 2017 study, and researchers found that it was only common in a few macaque groups that had spent a lot of time near humans. That suggests the behavior is something only certain individuals have picked up, and once they did, it spread to create a culture of thieves! And in case you’re wondering, yes, those researchers did have their stuff stolen, too, including their research equipment!

As for how macaques figured out this technique, people are probably at least partially to blame. For a long time, temple staff have been in the habit of feeding the macaques to encourage them to hang around—because they’re culturally and spiritually important to them, and because tourists like them. And once the monkeys learned that people had food, it didn’t take long for them to figure out that those people would trade food to get back pretty much anything else taken from them.

These are just a few fascinating examples of nature’s bandits, and this episode could go on forever, because the world is literally full of thieves. Sometimes, being a successful thief is all about muscle: being big or tough like cuckoo bees means you can take whatever you want. On the other hand, some research has found that brain size correlates with successful thieving—like the smart drongos and macaques on this list.

But even burglars in nature are usually just supplementing their diet with stolen food. And that’s because relying on someone else to do the work for you—and your ability to steal from them—is a pretty big gamble. Thanks for watching this episode of SciShow!

If you liked learning about nature’s best thieves, you might like our episode about incredible animal engineers. And if you never want to miss an episode, be sure to click on that subscribe button. [OUTRO ♪].