Most of our discussions so far have been on female ants (i.e. workers and queens) with little focus on male ants (drones). This is not because I dislike drones or find them uninteresting. The tragic fact is that there is far less research on male ants than on workers or queens. There are several reasons that make drones difficult to study. Drones are fleeting, rarely living for more than a few weeks. The timeframe to study them in the wild is incredibly small, and even if we know when they are likely to appear, their lifestyles make them difficult to observe. Newly born drones spend all of their time inside the ant nest until they are ready to mate. Mating often happens at specific times and places, and are near impossible to replicate in the lab. These combination of factors severely inhibits our ability to study these little guys and our understanding of them. Fortunately, some researchers have made it their life mission to further our knowledge of drones and show the world that they are not just reproductive machines (despite their name).
Drone biology
Drones are unlike their sisters and mothers in both appearance and behavior. Female ants (and us) are made from the combination of a sperm and an egg cell. Drones are special, they are born from unfertilized eggs. This means that they only have their mothers genes which causes them to develop differently from their sisters. Drones often have small heads and larger abdomens to support wings. Their gasters are sometimes elongated and their antennae may even be longer than their bodies. I have seen many biologists mistake male ants for wasps, even when they are right next to their sisters.
If you are an ant nerd and are interested in looking at more drones, I suggest checking out Alex Wild’s pictures of male ants. They perfectly capture the large variation in male ant anatomy.
While worker ants are usually aggressive and territorial, drones are often timid and docile (with some exceptions). They often live only long enough to mate and die soon after due to predation or even starvation. Some drones are known to empty their stomachs just before their mating flight to make them more aerodynamic. While this probably helps them more successfully mate, it ensures that they will die of starvation not long after. In the ant world, males live on as stored sperm within queens.
Life still ain’t easy
Even though their only job is to mate, drones do not have an easy life. Mating is competitive, messy, and stressful for just about all creatures in the animal kingdom. Most ant species mate using nuptial flights. Drones and princesses meet in a location and create a swarming mass of mating ants. The difficulty for drones (and princesses) is arriving at the location without being eaten by the numerous predators waiting for them. Sadly, things do not become easier for the drones that make it alive to the mating swarms. In their mating swarms, drones have to scramble to mate with a limited number of princesses. To make matters worse, some female ant species only mate once. The fight to be that one in a million is not an easy one.
How do princesses decide which drones to mate with? Unlike many species, ants do not have elaborate courting displays. Some ant species will only choose the bigger and stronger males while others may be less picky because of a phenomenon called postcopulatory sexual selection. Put simply, this is competition between sperm that is mediated by males and/or females after copulation. Some drones release spermicides (chemicals that destroy sperm) that kill the sperm of rival males when mating. Others use what is called a mating plug that prevents female ants from remating. Queens also have their own methods of controlling what drone will contribute to her offspring. Some can neutralize spermicides while others have complex valves that prevent sperm from reaching her eggs. Even if a drone succeeds in his mating flight, he is not always guaranteed to father any offspring.
Some ant species do not mate in nuptial flights. In these species, unmated female ants step just outside of their home nests and call for males by releasing pheromones into the air. Drones leave their nests in search for these pheromones and princesses. Once found, they will mate as usual. These drones have a greater chance of mating with a princess (they do not have to compete with a swarm of other drones), but they must find their princesses first. These princesses are more spread out and the only hope drones have to find them is to be lucky enough to locate her pheromone marker.
Interesting case of Cardiocondyla
Just when we thought we knew everything about ants, there is always one species (or genus in this case) that comes along to prove us wrong. In the previous section, we discussed the two main modes of mating: nuptial flights and pheromone calling. But, there is a secret third option that is only performed by drones in the Cardiocondyla genus. Instead of mating flights or callings, these ants mate within their nests. And to add to the lies I have previously told you, they make two types of drones: winged and wingless. These drones arguably have it the hardest out of all the drones we talked about before. As soon as they are born, they have to fight to survive.
As mating takes place within the nest, drones are involved in frequent and vicious fights for the colony’s princesses. The winged males act like typical drones of other species; they are docile and timid. The wingless males, however, are always out for blood; they will rip each other apart using large mandibles. To determine what factors influenced the outcome of fights between winged Cardiocondyla obscurior males, a group of researchers set up a fighting arena (a fairly common experimental setup in ant research). Unsurprisingly, they found that older drones were often victorious over younger ones. Unlike in other species, wingless drones live for more than a week. This was especially true for males that were less than 2 days old and were not fully developed yet. Older males often patrol around unhatched eggs and pupae so that they could kill any new drone that emerges. The only way for newly born wingless drones to escape this culling is by mimicking chemical signals produced by unhatched females until they are old enough to fight back.
You may be wondering how the winged drones factor into this bloodbath. As stated before, the winged males are timid and rarely, if ever, engage in fights. Their primary purpose is to leave the nest and join a new one to mate. This may prevent the negative effects that arise with breeding exclusively in the colony (known as inbreeding). It is interesting to note that not all Cardiocondyla species produce winged drones, some species seem to have completely lost this ability. In these species, it is thought that the colony splits up once it becomes too large and forms two, separate colonies.
In conclusion
Drones were long thought of to be nothing but mindless sperm banks by many myrmecologists. Recent research has shown us the exact opposite. Like their sisters, drones are complex despite their (often) singular goal of mating. Cardiocondyla drones even go so far as shattering what we once thought were true about all male ants. Perhaps in the future we will learn more about the hardships of these elusive little guys and upgrade them from drones to princes.
Bibliography
https://books.google.be/books?id=v7lV9tz8fXAC&pg=PA141&lpg=PA141&redir_esc=y#v=onepage&q&f=false
https://www.antwiki.org/wiki/images/9/94/Baer%2C_B._2011._The_copulation_biology_of_ants.pdf
Baer, B. (2020). Sexual Selection in Social Insects. In: Starr, C. (eds) Encyclopedia of Social Insects. Springer, Cham. https://doi.org/10.1007/978-3-319-90306-4_104-2
Bees, Wasps & Ants Recording Society, 2013. Formicoxenus nitidulus. https://bwars.com/ant/formicidae/myrmicinae/formicoxenus-nitidulus. [2nd February 2025]
Baer, B. (2015). Female Choice in Social Insects. In: Peretti, A., Aisenberg, A. (eds) Cryptic Female Choice in Arthropods. Springer, Cham. https://doi.org/10.1007/978-3-319-17894-3_17
Heinze, J., Cremer, S., Eckl, N. et al. Stealthy invaders: the biology of Cardiocondyla tramp ants. Insect. Soc. 53, 1–7 (2006). https://doi.org/10.1007/s00040-005-0847-4
Cremer, S., Suefuji, M., Schrempf, A. et al. The dynamics of male-male competition in Cardiocondyla obscurior ants. BMC Ecol 12, 7 (2012). https://doi.org/10.1186/1472-6785-12-7
Cremer S, Sledge MF, Heinze J: Male ants disguised by the queen’s bouquet. Nature 2002, 419:897.
