What are ants doing in our house? (Antananarivo, Madagascar)


We are living in Madagascar. It is winter so it is dry. There is a stream of ants that pass through our living room. They don't do any damage and don't seem to be carrying any food. They are more active at night and we see ants with big jaws come too. There are also winged ants which seem to be escorted by the other ants. Some ants move to the side of the stream of ants and stop moving. Are they sleeping?
I would be grateful if you could elucidate their behavior.

Thanks,
Sam

P megacephala.jpg


Dear Sam,

Thank you for your interested questions about the ants passing through your house! Judging from the photo you sent us they are probably an invasive species of the very diverse genus Pheidole. This species is called Pheidole megacephala - the African big-headed ant - because of the large heads of the soldier worker caste, or majors as they are usually called. The three workers in your photo are of the smaller worker caste - the minors - with smaller sized heads and you can recognize the species by a combination of several characters, which are essentially:

they have two very discreet looking worker castes, both with two constricted waist segments between their mid- and hind-sections, their antennae are 12-segmented with a 3-segmented club at the tip, most of their skin (exoskeleton) is smooth and shiny, their midsections, legs and antennae are usually of lighter color than their heads and hind-sections, and in their introduced range they often occur in large numbers with workers from different colonies of this species not fighting each other, which would be normal competitive behavior in other native ants.

Also of importance is the fact that these ants were found inside your house, which is often the case with species that were introduced from somewhere else through human activities. In Madagascar, and many other areas around the world, this kind of ants and other invasive species are quite common, but mostly in and around human-modified landscapes. The African big-head ant is considered a pest species, and has been shown to kill or displace a large proportion of native species communities.

As to your observations: ants are usually opportunistic foragers and coming into houses is a common occurrence, especially in tropical and sub-tropical areas and during the winter time, when resources outside may become scarce and hard to come by. The ones with the big jaws are the earlier mentioned major workers, which often fulfill different tasks than their smaller sisters (ant workers are all females), usually the transportation or chopping of larger food items into smaller pieces, which can then be more easily carried and fed to the larvae by the smaller worker individuals. The winged ants which were being escorted - and thus protected against possible predators - belong to the reproductive castes, either young queens or males or both, that were leaving the nest for mating with their respective counterparts from other colonies and in order to found new colonies.

Finally, the ants that stood to the side of the trail were most likely not sleeping but possibly standing guard against other ants and predators. If you observe the ants along these trails for some time you can usually see a whole spectrum of different behaviors, as for example one ant feeding another with regurgitated food from her stomach, or some ants wandering off to explore another area of the house, looking for new food sources. You would see individuals communicating with and recognizing each other as sisters from the same colony by using their long, elbowed antennae moving forward and sideways from the front of their heads, which contain the olfactory receptors (their sense of smell). Some ants would be working in pairs or groups to transport larger food items back to their nest. And others - not bothered at all by our prejudices of the industrious, hard-working ant and maybe even some of those that you have observed 'sleeping' - would probably be just idling about.

Yes, in ants as in humans you can find very different characters: there is the dutiful type that always comes to work on time and never rests until everything is done and accounted for, and there are the sluggards and lazybones who are not very interested in working for the greater good of their society and oftentimes exploit the social system as good as they can.

Thank you for contacting us at Antblog!

Georg Fischer & the AntAsk Team


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