Do bullhorn acacia-ants sting? (Nick)


I have been interested in certain insects & also arachnids for many years.I happened to encounter your website today while doing a google search for images of velvet ant varieties.They have absolutely beautiful coloration so I was doing a search on those insects.I realize velvet ants are not ants & are wasps but nevertheless I thought your site was interesting.Is it true that Bull Horn acacia ants in South America have a very painful sting? Its not often insects have a mutual-beneficial relationship with plants & other insects though it does occur in a number of species.


Hi Nick,

Bullhorn acacia-ants have a sting rated as a 1.8 on the Schmidt Sting Pain Index. While not excruciatingly painful by itself, when these ants attack, they attack with the full force of the colony and will continue stinging for as long as they can. They are also incredibly aggressive and will launch themselves from their trees onto invaders with no regard for their own safety. The wisest course of action is usually to avoid these trees altogether. Once you come into contact with the ants it is easy to understand how they can so effectively protect their plants because they are so aggressive and unpleasant.

The mutualism between the acacia-ants and their host plants is rather unusual but similar behaviors have evolved convergently both within the acacia-ant genus (Pseudomyrmex) and in unrelated genera such as Crematogaster and Azteca. Mutualistic Crematogaster ants in Eastern Africa are even able to protect their acacia hosts from megaherbivores like elephants and giraffes. You can check out the citation below for more of the story.

Goheen JR, Palmer TM. 2011. Defensive plant-ants stabilize megaherbivore-driven landscape change in an African savanna. Current Biology 20: 1768-1772.

Thanks for your question and keep up the interest in arthropods!
Ben Rubin & the AntAsk Team

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