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Nature's Creepiest Metaphor: the Ant Death Spiral

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This video has been making the rounds lately, but I haven't seen a lot of accurate descriptions of what exactly is going on in it. The "ant death spiral" is a phenomenon noted seemingly only in army ants, which unlike other kinds of ants do not make permanent nests and are always on the move while they're alive. There are over 200 varieties of army ants, and apparently the type featured in this video are blind, and depend on smells to navigate. Typically they follow the scent-trails of the ants before them in the swarm. The death-spiral is an example of what happens when the swarm as a whole gets misdirected -- and a convenient metaphor illustrating the perils of follow-the-leader behavior in any society.

According to The Ant Room:

Beebe (1921) described a circular mill he witnessed in Guyana. It measured 1200 feet in circumference and had a 2.5 hour circuit time per ant. The mill persisted for two days, "with ever increasing numbers of dead bodies littering the route as exhaustion took its toll, but eventually a few workers straggled from the trail thus breaking the cycle, and the raid marched off into the forest."

The phenomenon was first observed in in insects in 1910 by the scientist W.M. Wheeler in his laboratory, who wrote:

I have never seen a more astonishing exhibition of the limitations of instinct. For nearly two whole days these blind creatures, so dependent on the contact-odor sense of their antennae, kept palpating their uniformly smooth, odoriferous trail and the advancing bodies of the ants immediately preceding them, without perceiving that they were making no progress but only wasting their energies, till the spell was finally broken by some more venturesome members of the colony.

If you're interested, there's another video of ant death spirals in Brazil here.

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Adria C. LeBoeuf
Ants Communicate by Swapping Spit
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Adria C. LeBoeuf

Some insects’ mouth-to-mouth exchanges transmit tiny molecules of hormones and other important chemical information, according to scientists writing in the journal eLife.

The spit-swapping behavior is called trophallaxis. Many entomologists who witnessed the behavior in ants and other social insects believed the bugs were using it to efficiently share food. But some researchers noticed that carpenter ants were trophallax-ing in non-dining contexts, like when one ant would return to its family after being away. The scientists wondered if the ants’ kissing juice contained more than just calories.

They brought lots of ants into the lab to sample what the ants were sharing. At first, the researchers tried just waiting around until one ant initiated trophallaxis, but that mostly resulted in a lot of waiting and very little fluid. Eventually, they figured out that they could gently squeeze the ants’ bellies until the liquid came dribbling out of their mouths.

The researchers ran chemical and genetic tests on the fluid to determine its contents, and they found all kinds of interesting things. The liquid did indeed include particles of food and digestive enzymes, but it also contained several growth-related proteins and a juvenile hormone that can influence an insect’s development.

To find out how these compounds might affect a trophallaxis recipient, the researchers added the juvenile hormone to the meals they were feeding adult ants. The adults passed the hormone-charged liquid onto their larvae. The larvae loved it. Individuals who had taken in the hormone were twice as likely as others to survive to adulthood.

First author Adria LeBoeuf works at the Center for Integrative Genomics in Switzerland. She says the ants could very well be using trophallaxis to decide which larvae succeed. “When the ants feed their larvae, they aren’t just feeding them food, they are casting quantitative ballots for their colony, administering different amounts of growth-promoting components to influence the next generation,” she said in a statement.

Larvae chosen to receive the liquid are being nourished in more ways than one. In some ways, LeBoeuf says, it’s a lot like mammals’ milk. It also suggests that “…the oral exchange of fluids, such as saliva, in other animals might also serve previously unexpected roles." Yum.

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Josh Cassidy/KQED
Watch These Peruvian Tree-Protecting Ants in Ultra HD
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Josh Cassidy/KQED

In the Peruvian rainforest, a mutualistic relationship thrives between Inga tree saplings and native ants. The young trees need the ants as defense, so insects don't eat their leaves. The ants get "paid" for this defensive role using nectar provided by the tree.

In this beautiful Ultra-HD video from Deep Look, we see how this relationship works—and how it breaks down when clever Riodinid caterpillars come along!

The moral of this story? Never trust ants to protect you.

For more discussion, read this KQED article. Also fascinating is this paper by Suzanne Koptur (PDF link) describing the same ecosystem. There's also a nice It's Okay To Be Smart video on ant/tree mutualism.

And if you enjoyed this, watch another Deep Look video: What Do Ants Do With the Leaves They Carry Around?

(Photo courtesy of Josh Cassidy/KQED.)

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