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Why Don't Ants Gain Fat?

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Why don't ants gain fat?

Matan Shelomi:

Insects can store fat, though if an ant is chubby under its exoskeleton I doubt many would notice.

More importantly, however, is that if an ant has extra calories, then she will share them with her nestmates! Ants have a social stomach or crop, which is a separate food-storage organ before their digestive stomach or midgut. When an ant feeds, she directs enough food to her midgut to meet her nutritional needs, and the rest to the crop. [I say "she," because all worker and soldier ants are females.] If she is hungry later she can move some to the midgut, but if another hungry ant passes her and taps her head with a special code using her antennae, saying "Feed me" in ant sign language, then the first ant will vomit out some stored food so the second can eat!

Since ants have no refrigerators or other way to store food (unlike bees, which store nectar and honey in cells in the honeycomb), this is the best way to keep food, especially when traveling and burning calories like an ant on patrol. Some ants take it to an extreme: the honeypot ants have members called "repletes," whose crop expands to a huge size, several times larger than a regular ant. These ants become giant balls of nectar, storing calories for the entire colony, staying in the nest and not doing anything other than taking in and dispensing sugary liquids.

This post originally appeared on Quora. Click here to view.

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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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