Ants and eucalyptus: an alliance with both advantages and challenges

They have been around since the Jurassic period and their number is estimated to be billions worldwide. In eucalyptus plantations, which are fairly common in Portugal, their functions are complex and diverse, influencing several aspects of biodiversity and forest health. Learn more about this small insect that may seem insignificant but plays a crucial role in the balance of ecosystems.

Highly social and smart, ants leave nothing to chance. Their entire existence and survival rely on a highly organised structure that, upon closer examination, appears surprisingly human.

There are many similarities: they move like an army, build cities, coordinate behaviours, split tasks, and cooperate among groups. They make war and simulate rebellions, enslave other species and destroy and consume resources indiscriminately, unfortunately, just like humans do. In addition, they cultivate fungi, produce “vaccines” and care for their children and the sick, in a world strangely similar to ours.

This fascinating but unknown society was extensively studied and documented by biologist and myrmecologist (ant expert) Susanne Foitzik in several studies compiled in the book “Empire of Ants: The Hidden World and Extraordinary Lives of Earth’s Tiny Conquerors”.

But ants’ remarkable feats are there in other aspects also, aside from its internal society structure. Ants are a fundamental component of biodiversity, assisting the functioning and balance of ecosystems. They revolve and aerate soils, allowing water and oxygen to reach the roots of plants and trees. They do composting and transport seeds. They are a vital part of this intricate and sensitive natural system.

True superheroes

In addition to being an essential part of the food web, eating a wide variety of organic material and providing food for many different organisms, ants are insects with superhero characteristics.

For a long time, it was hard to estimate the number of ants on the planet but a 2022 survey states that there must be about 20 quadrillion ants. An almost unpronounceable number, but which proves their importance.

Belonging to the Formicidae family, they have a body divided into three parts: head, chest and abdomen and strangely strong legs, known to carry up to 50 times their own weight. They have strong trap jaws, segmented antennae and compound eyes. They also have meta-pleural glands that segregate an antibiotic fluid that allows them to form a kind of chemical protection against aggression. They come in a remarkable range of sizes and colours, depending on the species, and most of them have a sturdy exoskeleton.

Anthills are complex social structures composed of different castes, including the queen, males, and workers. The queen is in charge of reproduction, laying eggs that ensure the continuity of the colony according to its needs. In other words, the queen can choose which type of eggs to lay, depending on whether the colony needs more males or workers. Males have the primary function of mating with the queen and, after that, they usually die. The workers, sterile females, perform several essential tasks, such as caring for the larvae, building and maintaining the anthill, foraging for food, and defending the colony.

Colonies can range from small communities with a few dozen ants to vast societies with millions of individuals. Communication between ants is mainly done through pheromones, which are chemicals that transmit different messages, such as danger warnings, food routes or identifications of members of the same nest.

Ants and eucalyptus forests

Ants are often found in eucalyptus plantations due to their ability to adapt to different environments. These plantations offer a habitat rich in food resources such as sap, honeydew (a sugary by-product excreted by aphids and other insects), and small invertebrates on which ants feed.

This type of plantation accommodates a wide range of ants, more than any other forest type, natural or planted. A meta-analysis carried out by the University of Lisbon and the  RAIZ Institute identified 25 species of ants, raising to 44 the number of those found in eucalyptus plantations in Portugal, that is, about 30% of the total number of ant species that exist in the country.

One of the main benefits of the presence of ants in eucalyptus plantations is biological pest control. These are natural predators of many non-honeydew-producing herbivorous insects that can cause damage to trees such as caterpillars and other arthropods. By feeding on these insects, ants help preserve tree health and reduce the need for chemical pesticides, promoting a more sustainable environment.

Also, ants can improve soil structure. Its digging activities help aerate the soil and facilitate the infiltration of water and nutrients. This behaviour can help tree growth, especially in compacted or low-fertility soils.

Despite its benefits, the presence of ants in eucalyptus plantations can also pose some challenges and have some negative impacts. Some ant species tend to protect aphids and other honeydew-producing insects in exchange for this sugary food. This mutual relationship can lead to increased populations of these insects, resulting in greater damage to plants.

It is also not beneficial when they spread pathogens or reduce the abundance of other natural enemies and pollinators. Bees, for example, avoid flowers colonised by ants, compromising the pollination service. Therefore, it is essential to understand its role in ecosystems and realise that it is a delicate alliance with advantages and disadvantages.

Did you know that…

• Ants are as old as dinosaurs, and unlike dinosaurs, they managed to survive the explosion that extinguished them and the ice age. These facts were reported in a Harvard University study that states that these small insects date back to the Cretaceous period, about 130 million years ago.
• Ants have six legs with three joints each and a hook-shaped claw. This claw enables them to climb the branches of trees. Their legs are very strong, enabling them to lift and transport 10 to 50 times their own weight.
• The ants’ life cycle has four phases — egg, larva, pupa and adult — and its average life expectancy is approximately 40 to 60 days.
• Ants communicate through smell using antennae. They have five different noses. The antennas help them not only to smell but provide them with the sense of touch and act as guiding mechanism.
• Despite its small size, the ant’s abdomen has two stomachs. One of the stomachs stores food for its own consumption, and the second stores food to share with the other ants.
• Each anthill or ant nest has its own smell and level of complexity. They can have only one entrance and one chamber, or be made up of dozens of ramifications with multiple entrances, tunnels and chambers.

Sustainable management and monitoring are essential

To maximise the benefits of ants in eucalyptus plantations and minimise negative impacts, careful management is essential. Promoting biodiversity on plantations can help balance ant and other insect populations. Planting assorted plant species, including native plants, can provide alternative habitats and food sources that support a wider range of fauna. Forests managed by The Navigator Company follow this Biodiversity Conservation Strategy in all forest operations they carry out daily, thus ensuring the diversity of fauna, flora and other natural values.

Ants play a vital role in eucalyptus plantations, offering significant benefits such as biological pest control and improved soil structure. However, their presence can also bring challenges, especially when involving invasive species or mutualistic relationships with herbivorous insects. Integrated and careful management is essential to balance these impacts, promoting a beneficial coexistence between ants and eucalyptus plantations.

Ongoing study of interactions between ants and eucalyptus trees is critical to developing a more effective and sustainable management strategy. By better understanding these complex relationships, we can improve crop health and preserve biodiversity, ensuring the long-term sustainability of eucalyptus plantations in Portugal.