Were these ants building a wall?



Greetings!
Today my nephew told me that he saw a bird fly into a window at his office. Later he went out and saw the bird, dead on the sidewalk. He went to lunch and upon his return he saw ants surrounding the bird and they appeared to have constructed, for lack of a better word, a wall, around the dead bird. He thought it was made of small pieces of gravel or something. Have you ever heard of this type of thing? If so, what were these ants up to??
Thanks!
Susan Gray

Dear Susan:

This is a common behavior among ants. There are various interpretations or reasons why they might do so.
- The ants may well have been building a sort of wall. A possibility is that the wall serves to help keep out other ants that might compete for the rich food source that a bird carcass provides for an ant colony.
- Another one is that the conditions on the surface of a sidewalk are rather harsh (hot and dry) for ants that are not moving (which would allow them to lose heat), so they may be burying themselves, so to say, to keep out of the full sun and stay a bit cooler.
- Finally, many ants place particles of absorptive material on moist prey as a means of soaking up the liquid, to carry home on relatively portable particles of drier material.
This is more typical of ants that have a relatively small crop (social stomach), including some ants in the subfamily Myrmicinae, army ants, and occasionally others. Ants with larger crops (other Myrmicinae, Pseudomyrmecinae, and especially, Formicinae and Dolichoderinae) can carry a surprising amount of the undigested liquid in this modified portion of their lower esophagus, then regurgitate it rather like a mother bird to share with nestmates.
None of these explanations is mutually exclusive, and the ants your nephew observed could have benefited from this prey-burying behavior in all these ways, and possibly others I have not even remembered to mention.

James C. Trager of the AskAnt Team

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