Slavery among ants

I was standing at the roadside, waiting for a friend, when I noticed the ants nurturing a batch of aphids on a stem. We had been walking through a large heathland and got separated on our way back to the car. I reasoned that my friend, being a curious biologist, probably found and stopped by something of interest, and so I had a little time to try and take a few shots of the ants activity. I have never really given ants a go before, so I had no idea which traits are typically used in identification. The idea was to take enough frames to identify them later at home. My first impression though was “Probably one of those red forest ants very clear from childhood memory (ouch).”

Formica sanguinea ants tending to lot of aphids

10 minutes later my friend showed up, I got up from the ground and we left for home. When I arrived home I showed the pictures to people who know stuff about ants. There wasn’t the slightest doubt as they proved my first impression wrong. It was the slavemaking Formica sanguinea. It’s Danish name translates literally to “Blood-red Raptor Ant”. Wow, awesome fierce name, what can it do?!

Put shortly, F. sanguinea raids nests of other species of ants, kidnap their young, and raise to work in the nests of F. sanguinea. They often raid the nests of the common black ant Formica fusca, in Danish known as Black Slave-ant. Because of this behavior quite a lot of studies have been done on this ant and species with similar work ethics, and lots of mention can be found throughout literature.

The following description of a F. sanguinea raid is made up of bits and pieces plucked from Talbot & Kennedy 1940:

A group of 14 started out rather slowly from the nest; these were followed soon by other clusters. Almost immediately some returned to the home nest so that soon the column consisted of ants going in both directions. It did not progress very rapidly for the first 15 minutes. Then there was a speeding up in progress because more ants went straight forward and fewer turned back so that an advance of 48 feet was made in the next half-hour. The line was a typical exploratory one, the ants forming a broad column about three feet wide and exploring every crack along this line. There was no constant front but the line simply faded into a few scattered individuals making a fan-shaped end. There was no excitement and the ants moved slowly.

(..) (a bit later) There were many more ants on the trail which was now but two feet wide, and they were traveling fast. The trail ended (..) in a great mass of ants gathered in a grassless area three feet in diameter which was scattered over with bits of burnt wood one-half to one inch long. Obviously a nest had been located, but it was a “plugged nest”, that is a fusca nest whose openings had all been plugged shut by its own members. The sanguineas were exhibiting tremendous activity, exploring the area in minute detail and moving every bit of burnt wood encountered. At two places there was what seemed to be frenzied activity, with masses of reds tearing out bits of wood and exploring every crevice thus exposed. Evidently they were attacking two plugged entrances. Within ten minutes, one opening was penetrated and reds began disappearing in groups of 6 or 8. Immediately the first 4 black ants were routed out. Two of these walked quietly away, but the other two were pulled about a bit before being released. Within three minutes, there were streams of blacks pouring from both openings. Some were mauled but many were allowed to run away unmolested. Blacks continued to pour out for the next four minutes before a sanguined appeared with the first pupa. From then on blacks, and reds with pupae, continued to leave the nest while other sanguineas found and unplugged more openings. A black queen which had emerged was halted once but dodged, away into the grass.

This event took place over two days, with the finding of the nest and the actual raid happening in the middle of the second day. The morning of the third day, individuals of F. sanguinea where carrying F. fusca pupae in a constant stream along the trail back to their own nest. Meanwhile the escaped F. fusca ants were gathered in small groups around their queens in close proximity of the nest, waiting for F. sanguinea to finish up, so they could return to their, pretty much empty, nest.

A single F. fusca - The slave working among its masters.

F. sanguinea do not always suffice to just raiding nests. Sometimes they orchestrate a hostile takeover, moving most of the individuals (being workers, larvae and pupae) from the original nest to one of ex. F. fusca after clearing out hostile workers. Talbot & Kennedy 1940 reported a colony moving between alternate nests for 4 years before returning to the original nest.

F. sanguinea tending aphids

Having read about these ants now, I regret only spending the best of quarter of an hour watching them. They are definitely on my list of Must-See species for next year!

Stuff to read if interested:

The Ants - Bert Hölldobler & Edward O. Wilson - 1990

Talbot & Kennedy 1940: Mary Talbot and Clarence Hamilton Kennedy - “The Slave-making ant, Formica sanguinea subintegra emery, its raids, nuptual flights and nest structure” - 1940 - Annals of the entomological society of America - no. 3

Post at antblog.co.uk on F. sanguinea