Saturday, August 6, 2011

1 Queen, 2 Queen, 3 Queen, 4

Colonies of Tapinoma sessile, Odorous House Ant, normally stay outside. They thrive in places where there's lots of grass, and debris laying around. I've also found then nesting in hollow cavities in logs, and mason bee tubes. They're opportunistic and will nest anywhere they can. The common name comes from their habit of nesting in homes. The odor only occurs from crushing them so it might be better to discourage them than to fight back. They don't do a whole lot of nest building so sealing up where they're coming in from is an easy option if applicable. The smell is nothing unbearable I'm told. 

Shortly after their mating season, April to June, (occasionally July), queen number for each colony jumps drastically. Presumably they are either inbreeding within the nest, or colonies generally accept queens they come across into the nest.  

This leads to a lot more queens suddenly appearing into the nest and fuels budding behavior. At some point in the year colonies will divide as needed to setup new nesting sites elsewhere. Once divided colonies typically don't want anything to do with one another. The more urban the location though, it seems the more connected these colonies remain and they end up getting much larger than they would out in a suburban or rural area. There's something about city life that encourages colonies to stay connected in a series of sub-colonies as opposed to setting up new ones. What's neat though is that individual queens are fully capable of starting a colony on their own.

This kind of variation within a single species I've learned is more common in ants than previously thought. I've seen this in Monomorium minimum, both queen inbreeding, and loan queen colony founding. The Red Imported Fire Ant, Solenopsis invicta, do this too. With fire ants it's more genetically divided. Monogynic (one queen) colonies produce monogynic colony founding queens while polygynic (more than one queen) reproduce by queen adoption and budding. What's really neat about fire ants is their reaction to water. When floods come, all the members of the colony form a living raft and float away, but while adrift there's nothing stopping two colonies from bumping into one another. Floating for survival is no time for war, so the two colonies may merge into one floating raft, and upon reaching land they remain as one colony regardless of mono or polygynic status before the flood. Perhaps this is how polygynic colonies got their start with this species.  

I've seen colonies of Temnothorax sometimes combine to better survive the winter. The following spring they disperse and go their separate ways, though it's unclear if the workers are pared with their genetic mother or just going with the flow. Camponotus pennsylvanicus colonies are strictly monogynic but they still produce sub-colonies as extensions of their nest and territory. Each autumn these satellite locations are abandoned to better overwinter in one location. 

Perhaps the most notorious ant to talk about queen number is the Argentine Ant, Linepithema humile. In North America at least, this species spreads exclusively by budding. Queens mate inside the nest causing their numbers to skyrocket at one time of the year. Workers in L. humile have very high standards when it comes to queens though and each year they kill off ~90% of their own queens. This massacre occurs at the same time of year each year. It would seem they don't like their queens to be more than a year old, perhaps to maintain queens at the peak of their egg laying capacity. 

Though the queens to polygynic colonies ultimately produce larger colonies, their monogynic counterparts typically live longer.