For anyone who has visited the Bug Zoo before, it’s hard to argue that the ant colony spanning an entire wall is not captivating and awe inspiring in its whirlwind of activity. Even for seasoned staff members, it’s easy to be pulled into the coordinated restlessness the ants display, despite spending years watching them. The Bug Zoo actually boasts the largest captive ant colony in North America (possibly the world) with about 2 million ants in its prime. This may seem massive, but comparatively, a wild colony could have up to 7 million ants and have an underground colony spanning a space as large as an acre. But today isn’t the day we talk about the underground empires of the leaf cutter ants Atta cephalotes. Instead we’re going to delve into the reproductive side of things and discuss why the Queen is the only indispensable member of the colony, and easily the most interesting.
Picture spring time in a Brazilian forest, the air humming with activity and anticipation. Anticipation for the leaf-cutter ants nuptial flight, where all the newly created princess and drones(males) have a spring break of their own, and spend a two week period mating. After which the drones have done the only job they were created for and will die, never to meet their millions of daughters. Each princess has now likely mated with multiple males, 6 on average, and has all the sperm she needs to produce workers for the rest of her life. Up to 15 years. Nope, you didn’t misread that, not a typo either. This princess if able to store sperm and keep it viable for 15 years. This feat alone sets her apart in the eyes of entomology and science! She has a specialized organ called a spermathecae where these hundreds of millions of sperm cells dwell until she is ready to use them. Despite decades of research on these ants, it is still not entirely understood how she can do this. She is the ultimate reproductive being.
Now since this princess has over a decade worth of sperm to use, she needs to find a good spot to settle down and establish a nice colony for her daughters. There is only about a 5-10% success rate in a princess surviving the nuptial flight and establishing a colony, which is why these ants haven’t quite taken over the world (yet). Once a spot has been deemed worthy of her, the princess excavates a small chamber below the ground and eats her wings. She makes this potentially debilitating sacrifice so that she has enough energy to start producing eggs, how many mothers are that committed to creating a good life for their children? Many of these eggs, up to 90%, will be trophic and will be eaten by the now Queen ant or fed to her first generation of larva. Perhaps you’re questioning how good of a mother she is when you consider that piece of information, but keep in mind she needs to do this to have enough energy to continue producing eggs. Once she has established her colony, she will begin producing eggs at a rate of 1 egg every 3 seconds. For her entire life, which to reiterate is up to 15 years. This hardworking lady doesn’t have nights or weekends off either. A full lifetime will allow the Queen to produce between 150 and 200 million eggs. If you’re not impressed with this regnant yet, you’re in the wrong place.
As you’ve already read, the ant society is significantly biased towards female reproduction rather than male reproduction; drones are produced once a year and die off after about 2 weeks. To explain this essentially maleless society, we have to step into the biology of these ants. All hymenoptera, which includes bees, ants and wasps, are what we call haplodiploid. Essentially what this means is that males are haploid, and only contain one set of chromosomes, meaning any unfertilized eggs will develop into a male .Females on the other hand are diploid, contain 2 sets of chromosomes and develop from a fertilized egg, which is why the Queen needs all that sperm! Another way of thinking about it is that each female ant has two parents, while male ants only have a mother. No sperm needed to create a bouncing baby boy in this case! All of the eggs the Queen will have throughout the year are fertilized and will develop into females. Each of these eggs will be full or half sisters, and all the larva hatching from these eggs have the same potential to become any size or ‘caste’ in the colony. What dictates the type of ant the larva will metamorphose into depends on how much food it’s given; a larva eating lots of food develops into a larger soldier ant, whereas very little food (or no food at all) will cause the larva to develop into the smallest ants in the colony; caregivers and gardeners. In this case, nurture is more influential than nature. These various worker ants will likely only live for 2 months, explaining why the Queen can feasibly produce an egg every 3 seconds without running out of space. It has been observed that the Queen may reduce her rate of egg production as a result of spatial or food constraints; essentially once the colony reaches carrying capacity the rate may slow down. This is seen most easily in captivity.
Our ant colonies at the Bug Zoo are limited by the amount of space we give them, and unfortunately we have a finite amount of space. But how does the Queen know when she has run out of space? Certain cues are given to the Queen through pheromones from every soldier ant in the colony on a daily basis, now we can’t simply ask the ants what information they are communicating, but it is assumed that the main purpose of these interactions is to keep the Queen updated on the happenings of her colony. Remember she is rather busy producing all those eggs, so she can’t personally go around monitoring the colony herself. There are at least 20 pheromones that have been identified in leaf cutter ant communication, and although that number is likely quite low compared to the true number, it is reasonable to speculate that one of those pheromones may be used in telling the Queen they’ve run out of space. Cues like this are important to the health of the colony, as an unregulated increase in ants into a finite space severely decreases the quality of life and allows for disease propagation. One way to limit the number of eggs hatching into ants in the colony is to start eating some of those eggs!
One of the most common questions we are asked at the Bug Zoo is “Where’s the Queen??” usually with varying degrees of urgency reflecting how much sugar the questioning child has had that day. Depending on the day, that can be a tough question to answer. Often the Queen is in the back of a chamber, away from the light and the curious eyes of our visitors, which makes it difficult to place exactly where she is beyond an educated guess. That being said, it makes it even more exciting when the Queen is visible! The first time I saw the Queen, I didn’t know what I was looking at. A throbbing, wiggling mass of tiny caregiver ants caught my eye during one tour, which to my surprise, had a massive leg sticking out of it. Although I’m sure at that moment I wasn’t particularly eloquent in getting across to the tour group my thought process on what was happening, I eventually stumbled out “THE QUEEN!” and had a rush of children pushing me to get a better view. I have seen this lovely lady less than 5 times in a year and a half of spending the better part of my days in the zoo, which should tell you what a rare occurrence it is! Those teensy ants I mentioned covering her Majesty are caregivers whose main job is to look after the Queen; they are constantly cleaning, feeding and transporting her where she needs to go as well as taking away those eggs she produces and tending to them. It’s also been observed that they will sometimes massage her throat so the food goes down by mechanical manipulation and the Queen doesn’t have to swallow. She may be a hard worker, but being the Queen does have its perks.
Being a Queen has it’s perks, but it is also a very difficult job. Which is why not just any ant can be the Queen. Each springtime in the wild, all of the Queens in established colonies get specific environmental cues; pollen, temperature and pheromone changes. This causes the Queen to refrain from fertilizing a some of her eggs, allowing them to develop into drones, and also allows princess to develop, hopefully setting them up for life as a future Queen. Nuptial flights occur soon after this, with all these fertile individuals flying from their natal colony and vying for the attention of the opposite sex while in midair. Often this will end with a princess stuck on the ground with drones clambering for a chance to mate. Not the most romantic mating process, but the princess is trying to mate with multiple males to increase the diversity in her future colony, setting herself up for a more disease resistant colony. Environmental cues like the ones mentioned are essential for syncing up the nuptial flights of all the ant colonies in the area. It wouldn’t be beneficial for the next generation if each Queen picked an arbitrary time to create princesses and drones.
Captivity presents the issue of a relatively stable environment; none of those cues required for signalling are present, which in theory should prevent any princesses or drones from being created. But, as we know from Jurassic park, life finds a way. About three months ago, in September of 2017, we noticed a total anomaly. A large winged individual in our 14 year old colony. We know that it couldn’t have been the Queen because of the wings, and regardless this ant was smaller than the Queen. To say the least, we were flabbergasted. All of our combined knowledge and research on these ants left us high and dry in this situation. We scoured pages of other zoos with the same species, read research papers with more authors than we have staff here, and still found nothing that could help us figure out who this individual was, and how it got there. So, we did just about the only thing left to do. We watched. This ant wasn’t doing too much, it was moving around a little bit, and being cleaned by caregivers. Not to the same extent as with the Queen, but it seemed like they were still finding it to be an important member of the colony.
As with any exciting event at the Bug Zoo, this caused a mild uproar in the staff. Not only were we thrilled and shocked to have this happen, but also very confused. Confused about how it happened, and what this ant was. As a staff we still don’t entirely agree on if this is a very long lived drone, or a smaller than normal princess, so if you pop into the Zoo for a visit you may get to hear multiple hypothesis about this ants chromosomal number!
Expectancy was palpable the following month and a half after the discovery of this ant in the colony as we tried to decipher what its purpose was. Rather suddenly and in an underwhelming fashion, this ant did what all things do eventually; it died. This poor, unfulfilled ant was found in the waste dump with all the other discarded refuse of the colony, an unfortunate demise for an individual filled with so much potential. As if this colony had not experienced enough hardship in the fall of 2017, the end of November brought another impactful death; the Queen. Her reign lasted over 14 years, and she died the way she lived; covered in her enthusiastically cleaning daughters. As morbid as it sounds, these caregiver ants are still cleaning the Queen’s body about a week after her death. Their commitment is unwavering to say the least.
Now at this point, you may be asking yourself how the colony continues in captivity once the Queen dies. In short, it doesn’t. Certain hymenoptera may have hierarchies or multiple Queens at once, enabling the continuation of a colony, but for Atta cephalotes the death of the Queen is the end of the colony. This is true for in the wild and in captivity; princess’ need to leave their natal colony, mate, and then start their own colony. Regent death is followed by a slow dwindling of activity over 2-3 months, as the daughters of the Queen continue their jobs until they die, unreplaced by new ants. In all honesty, it’s a rather demoralizing sight watching the colony fade from its former glory. But, with death comes the potential for new things! A not so well kept secret at the Bug Zoo is that we have a starter colony in the back for just this occasion. Once the rest of the old colony has finished their life cycle, we shall clean out all of the ant chambers and introduce the new colony, starting the reign of a new Queen.
Leaf cutter ants are a highly studied animal, for good reason, there are entire books written on them in fact! But as with all things in science, there are disputes over facts and statistics. Things change as we learn more, and more often than scientists would care to admit, we have no idea what is going on! With that information in mind, I ask you to take all I say with the understanding that there are different sources contributing to what I’ve written. Different sources sometimes have slight disparities, and to make everything as cohesive and relevant as possible, I’ve used the information that I understand to be the most accurate from research of the literature and personal observation. That being said, there is a whole world of information out there on leaf cutter ants, or ants in general and there are so many things about these ants I didn’t even touch on. If you have any interest in learning more about these ants, some indispensable (and enthralling) resources I would recommend include: The Leafcutter Ants: Civilization by instinct or(and) The Superorganism: The beauty elegance and strangeness of insect societies both by E.O. Wilson and Bert Holldobbler. Another personal favourite is Adventures among Ants by Mark Moffett. These authors kept me up way past my bedtime as their excitement and passion shines through in their words and photographs to instil a sense of childlike wonder for these creatures. If that doesn’t satiate your curiosity, come by and talk to us! We are always happy to discuss all of our animals, but if you’re not careful you could be signing yourself up for an easy 45 minutes of ant-rants.
Long Live the Queen!