Parasitic Ants Shake Up Colony Society
In Evolutionary Twist, Unusual Ant Colony Lives Off Others
By Lee Dye Feb. 5, 2011
Slaves vs. Parasites
… The acorn had tiny ants, each about the size of the tip of a ball point pen, and Johnson put them under a microscope for a closer look at a “really weird looking queen,” Herbers recalls.
“‘I went over there and looked at it and said ‘Oh my god, you’ve got minutissimus.”‘
Leptothorax minutissimus had only been found in four other areas of North America, and the species has baffled biologists ever since it was discovered in 1942 in Washington, D.C. The species has evolved to the point that it no longer has worker ants that forage for food and carry out other chores.
“It has lost the worker class,” Herbers says. Only queens are left.
So to survive, the ants must invade another colony and take up residence as parasites. Herbers wants to find out how they do that without bloodshed. That’s a very different lifestyle from the “slave maker” ants she has studied for so long.
“Slave makers will enter a host colony and start pitched warfare,” she says. “They kill off any adults that try to resist the attack. What they are after is not the adults, but the larvae. They steal the larvae and take them back to their own nest and wait for them to hatch out as worker ants.
“One thing that’s peculiar about ants is they learn who they are by smell only after they have hatched and become workers. These slave makers can exploit the fact that the larvae have no idea where they belong. If you can get them when they are young enough, you can indoctrinate them to be slaves,” Herbers says.
So how does minutissimus manage to live in harmony as a parasitic resident in another species colony?
Herbers is launching an investigation to learn “how these ants make a living,” as she puts it. They must be doing something worthwhile or the host would kick them out.
Seeking a Model
Herbers expects to find many other colonies this summer, now that she and her researchers know exactly what to look for, and they hope to piece together the social evolution of the diminutive minutissimus. How, and why, did it evolve into a benign parasite?
Some of the ants they hope to collect will be put through a series of tests in the lab to see how they react to different situations. For example, a colony of host ants will be put into a small box, and a minutissimus queen will be put in the same box, a little ways away from the nest.
“We’ll watch to see if she zooms right for the nest, or if she wanders around, or if she’s killed when she tries to get into the nest,” Herbers says. “We don’t know any of that stuff.”
By the end of next summer, she hopes to have a few more answers than she has now. But, one may wonder, why all this fuss over a bunch of ants so small you almost need a magnifying glass to see them? […]
Our analysis shows that xenobiotic parasites tend to have single or multiple host species that are very distantly related and have medium to large host colonies. Temporary parasites tend to have multiple host species that are very closely related and have medium host colonies. Dulotic parasites tend to have multiple host species that are slightly less related and have host colonies of any size. Lastly, inquiline parasites tend to have singhttp://eebweb.arizona.edu/faculty/dornhaus/labwww/projects.htmlle host species that are very closely related and have medium host colonies. In addition, a parasite tends to be very closely related to its host when the parasite has a single host species or large host colony sizes.
Panama; captive colony at the University of Texas
Socially parasitic ants are usually discernable by their relatively small queens, as ants that start new colonies by infiltrating existing nests do not need large body reserves. The queen of Aphaenogaster tennesseensis- a temporary nest-founding parasite of several other woodland Aphaenogaster- is scarcely larger than her own workers.
Urbana, Illinois, USA
Solenopsis (Labauchena) daguerrei (Santschi) is a parasitic ant of fire ants in South America. This parasite produces no worker caste, and is totally reliant on its host colony for its care. Having no worker caste, only reproductive males and females represent this species. S. daguerrei will attach, or yolk, themselves to queens of the black and red imported fire ants, Solenopsis richteri and S. invicta, respectively, and divert resources from the host queen(s). In addition, the host colony also feeds and maintains the brood of S. daguerrei. Thus, S. daguerrei is a potential stress factor of fire ant colonies.
Field studies and observations of the impact of S. daguerrei on the fire ant, S. richteri, are being conducted in sites located in Argentina by ARS scientists at the USDA-ARS South American Biological Control Laboratory in Hurlingham, Argentina . Average percent parasitism from pastures located at 21 sites was 5.1%. Mound densities were 33% less in sites with S. daguerrei and the number of fire ant queens was 47 % less in parasitized colonies.