June 2013 Archives

Territorial battles



Hello from Brookfield, Wisconsin.

It's great to see this service online--yet another wonder of the Web.

My question involves small (not much over a millimeter long), red ants that nest around our home and seem particularly to like areas near our front walk.

More than once I have noticed these guys flowing onto the concrete and forming a large gathering in the open air--see attached photos.

Why do they do this?

Thanks,
Ted

Small Red Ants 1.jpg

Small Red Ants 2.jpg


Hi Ted,

These are a species of pavement ant, Tetramorium caespitum. They are common in urban areas, hence their common name. The event pictured is a large territorial battle between colonies. Territoriality is common in ants as a whole, varying by species and colony age. Ants typically protect their territories for access to food or nesting space.

The closely related Japanese pavement ant, Tetramorium tsushimae, is similarly territorial to the pavement ants that you see in Wisconsin. In this species, colonies with larger territories containing larger numbers of seeds and other food resources are able to raise larger numbers of reproductive individuals. However, food is not the only factor determining colony success. The ideal temperatures for raising queens and males are between 27.5 and 30 degrees Celcius (81.5 to 86 degrees Fahrenheit) and colonies also engage in territorial battles to gain access to nesting sites with these temperatures. Therefore, the pavement ants on the sidewalks outside your house are probably fighting for access to both food and optimal nesting sites.

While fights among pavement ants often lead to the deaths of large numbers of workers, this is not a requirement for ants to maintain territories. A species of honeypot ant, Myrmecocystus mimicus, is also highly territorial, but, rather than risk the lives of workers, engages in ritual displays. Hundreds of ants from each competing colony confront each other and stand as tall as they are able while inflating their gasters to appear larger. Eventually, a winner is decided based exclusively on the differences in workers between colonies and territory is ceded to the apparently stronger colony. If colonies are drastically different in size then the smaller colony will be destroyed but otherwise, no physical interactions occur. You should take a look at the papers listed at the end of the post if you want to know more details.

Thanks for your question,
Ben Rubin, James Trager, & the AntAsk Team

Holldobler B. (1981) Foraging and spatiotemporal territories in the honey ant Myrmecocystus mimicus Wheeler (Hymenopera: Formicidae). Behavioral Ecology and Sociobiology 9: 301-314.

Sanada-Morimura S, Satoh T, Obara Y. (2006) Territorial behavior and temperature preference for nesting sites in a pavement ant Tetramorium tsushimae. Insectes Sociaux 53: 141-148.

Winged ants sendoff



Hi,
We've observed swarms of pavement ants all over the neighborhood and found out via the internet that this is to send off the winged queens and males to start new colonies. Assuming this is correct, I still have a couple of questions. First, why do so many worker ants need to swarm? Does this serve a useful purpose, like distraction or something? They just seem to be going in all directions (and occasionally moving pine needles and things). Second, as I was crouching over one swarm the ants dragging the winged ants seemed to switch directions and pull the winged ants back into the nest. Would there be a reason for them to do this, like because of my presence, or some other prompt, or was it just a coincidence?
Thanks,
Anne

Hello Anne -- Thanks for writing the antblog with this question, which I think will be of broad interest to ant observers. It is true, as you say, that ants send off winged individuals to start new colonies. These mate away from the parent nest, often in a mid-air swarm composed of winged ants from many different home nests, thus ensuring outbreeding. After mating, males soon die, but the females go to a suitable nesting site, break off their wings, build a small nest, and attempt to raise a batch of workers and thus become a colony queen. Most foundress queens fail, due to predation, desiccation, fungal infection, etc., which is why ants send out so many winged females during the life of the colony.
Ant colonies invest a lot of food and energy into brood rearing generally, especially into rearing the large reproductive forms. So they protect this investment the best they can for as long as they can, up until the last moment, when the winged ants fly off. A swarm of worker ants can intimidate potential predators from approaching the winged ants, and when they workers detect a giant form or shadow (such as yours), they try to protect their winged brothers and sisters by dragging them back into the nest. They also do this when changes in weather (sometimes even a mere gust of wind or small cloud blowing over) indicate possibly unsuitable conditions for a successful mating flight may arise. The more healthy winged ants they can keep alive for the eventual mating flight, the more likely it is a particular colony's genes will make it into future generations of their species.

James C. Trager of the Ask Ant Team



Hi,

I'm sorry if it's bad form to send pictures of dead creatures, but this particular one was acting belligerently in my bed, forcing my hand. I think I crushed its thorax in the act.

I encountered this insect while living in the central part northern Namibia, maybe 10km south of the Angolan border. I have no idea what it is. I've always wanted to learn more about it, and when I discovered this blog I thought it might be a place where I could get some guidance.

Can you identify this? Is it even an ant?

Thanks a lot,

Brent

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Brent,

No worries on bad form. Your inkling that this is not an ant was correct! This is a Solifugid, more commonly known as a sun spider, wind scorpion, or camel spider. Although it is an arachnid along with scorpions and spiders, most species of Solifugids do not have venom, and are not much danger to humans. The only thing you might want to watch out for is their powerful jaws, which they use to hunt ground-dwelling arthropods and other small animals.

Hope this helps!

Best,

Max Winston & the Ant Ask Team