Leaf Cutting Ants, In Nature, In Captivity, In Focus!
In Nature
Leafcutters are native to the New World Tropics and range from the southern United States down to Argentina. Throughout the countries where Attines are found they are the dominant herbivore, exacting a huge toll on the vegetation around them. It is estimated that Leaf Cutting Ants remove up to 40% of all plant growth, including crops and garden plants. Several species found in the open pampas of South America are specialised to gather grasses, whilst those found in the heavily forested tropics, synonymous with the jungles of Brazil and other Amazonian countries, will cut broad leaves and take advantage of the types of plants found there. A constant battle is fought in all these areas between farmers and these intractable opponents involving spraying, digging and burning and yet, such is the prodigious nature of Leaf Cutting Ants and their ability to adapt, not a single species has been threatened in any of their habitats. In fact, quite the reverse is true. Leaf Cutters enjoy open spaces where the sun can warm their nests in the morning and so as the rate of deforestation increases, so does the suitability of the terrain and, as a result, there are more Leaf Cutters. We are, in the case of this super organism, a victim of our own destructive behaviour.
Famous for their massive colonies and long foraging trails, Leafcutters form extremely complex societies and cultivate a special type of fungus which is only found nowhere else in nature. They have been growing crops for food for 65 million years, around 64 million years longer than we have been farming. The ants forage for leaves and, using their sharp mandibles, they are able to cut small discs which they carry back to their nest. Contrary to common belief, the ants don’t consume the leaves. A Leaf Cutting Ant nest is a vast conveyor belt in which millions of leaf fragments are carried into this processing facility and armies of tiny gardeners carefully clean them and chew them to a pulp. They add saliva and other chemicals and then add this fertiliser to the gardens. Into this nutritious mix they plant fungal mycelia which transform the media into the fungal gardens we recognise when observing the colony. The ants meticulously weed and tend the growing fungus to ensure that the fungal mass is a true monoculture. In return the fungus provides the ants with gongylidia (nutrient hyphal swellings known as fruiting bodies) which they consume. Other than ourselves, Leafcutters are the only other type of organism which is able to grow its own food with such a sophisticated system of farming and crop management. Also, as part of the management of the fungus gardens, the ants remove exhausted fungus from the base of the garden and take this to a dump area. Whilst some species, such as Atta colombica, form a mound of this refuse on the surface, most species form dump chambers underground, well below the fungus gardens. These dump chambers are filled with spent fungus over the 15 to 20 years of the colonies lifespan and serves to fertilise the nutrient poor land which demonstrates that, whilst they may be a serious pest species to us, they are a very important part of the biological story of their environment.
Leafcutters construct incredible underground nests, vast labyrinths of interconnecting tunnels and innumerable galleries housing rugby ball sized fungus gardens. Over the course of the life of a colony the ants are likely to shift up to 40 tons of soil. Their nest design is very specific; they build small turrets above ground which prevents the rain from flowing into their nest; these entrances allow for sufficient ventilation and there is also a hypothesis that the ants control the number of openings in accordance to the carbon dioxide levels inside the nest, to maintain precise conditions. As the heat generated from all of their massive subterranean activity rises up through the centre of the colony and out of the main entrances above, cool air is drawn down through peripheral tunnels and an extremely efficient air conditioning system is created which ventilates, cools and humidifies the entire city of ants. This fine control is necessary because of the exacting requirements of the fungus which we will discuss a little later.
Whilst it is not apparent to the naked eye when observing Leafcutters, they are under constant pressure to keep their fungus free of any foreign, invading fungi which could infiltrate their nest and ultimately destroy their crop. They constantly patrol their gardens protecting the fungus. The ants are further specialised, having the growth of a special kind of bacteria, Streptomyces, on the surface of their bodies. These bacteria are capable of destroying microbes by producing antimicrobial agents. The warm and humid conditions inside their nest, necessary for the fungus to grow, are also perfect for other foreign fungi and many of these will attempt to establish themselves in this favourable environment. This could potentially be a serious problem for the ants; however they are well equipped with methods to protect their precious crop. In a growing colony, some ants develop enlarged metapleural glands which secrete phenylacetic acid (PAA) which actively combats fungal infections. Leafcutter ants are amazing insects, they are able to produce antibiotics without suffering the damaging effects of antibiotic resistance. We, as humans, are losing the battle against antibiotic resistance. Researchers are looking into Leafcutters and how they are able to overcome this issue – we have much to learn from them!
In captivity
Since the 1930’s leaf cutting ants have been displayed in zoos and other public attractions around the world. Today few collections of animals are presented to the public without a display of these insects. They are a mainstay of Butterfly houses and Tropical Zoos and their ability to amaze and fascinate leads them to be one of the most popular attractions wherever they are on show.
To maintain a colony of these ants in your own home, as a hobby, may seem a daunting task but actually, today, the biggest challenge in doing this is finding the commitment and the passion to give it a go!! Leaf Cutters have never been so accessible in terms of colony availability and suitable housing, and whilst Atta species may well be potentially too big to manage, ants of the genus Acromyrmex are less populous and can be maintained at a manageable size in terms of numbers.
When you think of keeping leaf cutting ants it is best to consider that you are actually looking after both a colony of ants and a culture of fungus. Making this distinction is actually a very good way of understanding how to keep leafcutters successfully. In order to have a strong, growing colony of ants, both the fungus and the ants need care. However, the easy partner in this relationship is the ants. They will be active over a wide range of temperatures and they are largely unconcerned about humidity levels. The fungus is a different matter though. In almost every case we hear about a colony that has died, the cause is invariably the death of the fungus. In nature this fungal culture exists in environmental conditions that vary very little throughout a year. Deep in the underground chambers there is a constantly high humidity and a temperature that varies only around 1oC over the course of 12 months. Setting up an artificial ‘laboratory’ style nest requires that you provide for this in order to be successful. The easiest way to achieve this is to provide your colony with ‘wet’ heat. This means that any heat that reaches the ants has been generated from warm water. This water may be between a low wattage heat mat and the ants, or in a warm water bath surrounding the ants. Provided you avoid dry heat you are probably safe.
A good quality humidity meter and a thermometer, both fitted with a probe, are an essential piece of kit. You need to place the probes from these gauges directly into the fungus garden. It is not important how humid the air is 30cm from where the fungus is, its important what the humidity is right at the garden.
Keeping a colony of leaf cutting ants is by no means equivalent to keeping any other species of ants because leaf cutting ants require this constant environment in order to thrive. Whilst it is possible to provide for their needs by designing a setup based on a simple glass aquarium, there are specialised housing units, which are designed to accommodate their needs, available to purchase. These units provide an easy way to create an ideal environment for the ants and they are developing and improving all of the time as the demand and the interest grows. When established, a colony of leaf cutting ants needs only simple maintenance which includes changing their leaves daily and ensuring they are humid and warm.
One of the increasingly popular housing methods is that of a ‘clean’ setup, whereby no soil is added and view of the colony and fungus is not obscured. This is advantageous as you are able to assess the health of the fungus through visual observations and also able to access the fungus without fear of tunnel collapse in soil. This is an excellent choice for a hobbyist as you have total view of your colony. A small layer of substrate such as clay granules can be provided to absorb excess moisture and promote humidity. This is the method of housing we will discuss.
A series of basins can be utilised to mimic fungus chambers. The ants will initially begin with a single fungus garden and grow until the ants decide a new garden is to be started which is separate from the first one. Three basins, one for fungus, one for foraging and one for waste, are typically favoured at the beginning, set up as a modular design where one is able to add on extra units with ease.
Leaf cutting ants from the Atta and Acromyrmex genus require a stable temperature of 25°C with a maximum variation of ±2°C. It is important that the temperature is maintained as large fluctuations over a long period of time can be detrimental to the fungus. High humidity in the fungus chambers is extremely important, aim for between 70% minimum, ideally somewhat higher. This can be difficult to achieve at the same time as ensuring minimum condensation and sufficient ventilation. Water droplets falling on the fungus will cause it to decay and rot, so being able to maintain high humidity with minimal condensation is very important. Cleaning is not always necessary as the ants will nominate a dump chamber, usually the furthest away from the fungus, where they will deposit waste. Conveniently for the keeper, you will be able to remove the waste with minimal effort.
In the first six months of keeping leaf cutting ants the growth rate is steady, but after the first year, the colony will expand at an exponential rate. This is less apparent in Acromyrmex spp. as colonies tend to grow slower than Atta spp. but suitable preparations should be in place. Acromyrmex is favoured over Atta for private colonies as they tend to peak at around fifty thousand ants compared to Atta, which can grow to several millions. Atta have a soldier caste of workers whereas Acromyrmex do not so are less painful to interact with.
In Focus
20 years ago Leaf Cutting Ants were the preserve of zoos and Butterfly Gardens, an exotic spectacle to visit and stand amazed at the grand activity on show! Now, following an explosion of interest in keeping all species of ant, leafcutters find themselves in every captive situation, from schools, offices and libraries to bedrooms in private homes. Locating and buying a nest has also become less onerous. Over the past few years the price of a colony has halved and housing is commercially available from several suppliers around Europe. As our understanding of how to cater for their complex life histories increases, so the pleasure of growing these superorganisms becomes more and more accessible to all. This is the story of the start of a journey, a fledgling hobby where every week new ideas are shared and developed, every month access increases and the community grows. The fascination of leaf cutting ants is consuming and once you keep them you will be burdened with a life long passion for these most remarkable and fantastic of all organisms.