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Ants and Salt

When my very good friend Deb Sparrow sent me this photograph of a harvester ant collecting a piece of a blue corn chip that had fallen from her lunch, I immediately took it at face value. A harvester ant carrying a corn chip seems like an obvious combination. After some research, however, I am beginning to wonder whether the ant was also interested in another, not so obvious, aspect of the corn chip.

ant-blue-corn-chip

Photograph by Deb Sparrow (near the Hassayampa River in Arizona)

Recent research has shown that certain ants collect salt (sodium chloride). Michael Kaspari, Stephen P. Yanoviak, and Robert Dudley presented different species of ants baits with varying concentrations of salt (NaCl) versus two concentrations of the standard bait attractant, sucrose solution in water.

The scientists found the ants responded to the salt solutions depending on their distance from the ocean. Ants near the ocean presumably would have more salt available, carried to the land by wind and storms. In general, the further from the shore, the more the salt solution attracted ants and the steeper the dose response.

One interesting exception, however, were ants that generally are thought of as carnivorous, for example fire ants of the genus Solenopsis. The idea is that carnivorous ants get their salt through their prey, whereas vegetarian species, like the harvester ant above, would need to supplement their diet. The researchers also found that ants of the genus Pheidole did not respond to salt. The diets of many Pheidole are not well-studied, but at least a portion are also seed harvesters.

Guess I’ll be paying more attention to ants and salt from now on. I have to say that here in Arizona our water, and thus irrigated soil, is full of salts. In fact one of our main rivers, the Salt River, is named for the natural salt springs that feed it. Maybe our natural abundance of salt is one of the reasons why we have such a variety of ants.

What do you think of ants and salt?

References:

On the biogeography of salt limitation: A study of ant communities by
Michael Kaspari, Stephen P. Yanoviak, and Robert Dudley.
Proc Natl Acad Sci U S A. 2008 November 18; 105(46): 17848–17851.

Ants More Attracted to Salt Than to Sugar by James Parker for The Daily Californian

The biogeography of sodium limitation by Dr. Michael E. Kaspari at The AntLab. Also see link to pdfs of his papers.

Inland Ants Crave Salt, and Hurricanes May Help by John Roach for National Geographic News

Edit:  The Circus of the Spineless is now up at Greg Laden’s Blog

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6 comments to Ants and Salt

  • Fascinating! I’ll have to start offering salt to my assorted critters.

  • Hi – I am visiting from CotS. This is very cool. I have never thought of the relationship of any animal to salt, much less ants. Thanks – I learned something new today.

  • Roberta

    This weekend I made some observations that seem to indicate at least some birds are interested in salt too.

  • Nicole

    I have ants collecting salt in my garden at the base of our house….I’m wondering where it is coming from and why they are there…does any one know???

  • Roberta

    Are you sure they are going after salt? It is known that ants need salt in their diets just like most animals do.

  • nick

    I found your story from searching “ant and salt”. Why was I searching that? you may ask. Because this morning I found 2 ants trapped in my salt shaker which is probably the 3 time already this week. Then also a bunch of black ants got into my fish sauce(dark asian sauce full of sodium). All while there was 2 box of donuts near-by untouched by ants. The ant’s behavior is just a bit unexpected this year.

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