Messor structor (The Steppe Harvester Ant)

Introduction

Messor structor is a fascinating and unique species of harvester ant that stands apart from many of its cousins. While most Messor species are strictly monogynous (one queen), Messor structor is one of the rare exceptions that is often polygynous, meaning a single colony can house multiple queens. This biological trait allows their colonies to grow rapidly and reach enormous sizes, creating a bustling metropolis of activity within the formicarium. Known as the "Steppe Harvester Ant," they are rugged, industrious, and highly adapted to life in open, dry landscapes.

For ant keepers, Messor structor offers a slightly different experience than the more common Messor barbarus. They are generally more active and less skittish, and the possibility of keeping multiple queens in one setup is a major draw. Watching these ants engage in "bread-making"—the process of chewing seeds into a nutritious paste—is a classic ant-keeping experience that never gets old. Their impressive polymorphism and the presence of massive-headed majors make them a favorite for enthusiasts who love "big-headed" ants.

Taxonomy and Distribution

Messor structor is a member of the subfamily Myrmicinae. The genus Messor is famous for its specialized seed-gathering (granivorous) behavior. For a long time, M. structor was considered a single widespread species, but recent genetic studies have revealed it to be a complex of several closely related species. However, in the hobby, they are still widely recognized under the name Messor structor.

Their distribution is vast, stretching across Central and Southern Europe, through the Balkans, and into parts of Western and Central Asia. They are typically found in open, sunny habitats like steppes, meadows, and agricultural fields. They prefer dry, well-drained soils where they can excavate deep, complex nest systems that protect them from the extremes of the weather. Unlike some Mediterranean Messor species, M. structor can be found in more temperate continental climates, making them quite hardy.

Physical Characteristics

Messor structor is a highly polymorphic species, meaning there is a significant size difference between the smallest workers and the largest majors. Minor workers are roughly 4-6mm in length, while the impressive majors can reach up to 10-12mm. The queens are substantial, usually measuring around 12-15mm. One of the most striking features of the majors is their massive, square-shaped head, which contains the powerful muscles needed to crush even the toughest seeds.

In terms of coloration, Messor structor is generally a dark, matte brown or black. Unlike the red-headed Messor barbarus, M. structor maintains a more uniform, earthy tone that reflects its life in the dry steppes. Their bodies are covered in fine, pale hairs, and their legs are strong and built for carrying heavy seeds over long distances. Their mandibles are thick and serrated, perfectly evolved for the mechanical task of processing grain.

Colony Behavior and Social Structure

The social structure of Messor structor is one of its most interesting features. While they can be monogynous, they are frequently found in polygynous colonies with several queens living together in harmony. This leads to a very stable colony that can withstand the loss of a queen more easily than other species. Colonies can grow to tens of thousands of workers, forming massive networks of tunnels and seed storage chambers.

They are relatively docile compared to some aggressive Myrmicinae but are very defensive of their nest. One of their most famous behaviors is the creation of "ant bread." Foragers collect seeds and bring them back to the nest, where other workers husk them and chew the kernels. They mix the chewed seed with saliva and water to create a paste (the "bread"), which is then fed to the larvae and the queen. This unique diet allows them to thrive in environments where insect prey might be scarce.

Diet and Foraging

As harvester ants, the primary diet of Messor structor consists of seeds. They are not picky and will collect a wide variety of grains, including grass seeds, dandelion seeds, and even specialized seed mixes sold for birds or ants. In captivity, it is essential to provide a diverse range of seed sizes to accommodate the different sizes of workers. Minors can handle small seeds, while the majors are needed to crack the larger, tougher ones.

While seeds provide the bulk of their carbohydrates and some protein, they also benefit from occasional insect protein. Feeding them crickets, fruit flies, or mealworms will boost the growth of the brood and ensure the health of the queens. Unlike many other ants, Messor structor does not rely heavily on liquid sugars like honey or sugar water; they get most of their moisture and energy from the seeds themselves and from drinking plain water.

Life Cycle and Reproduction

The life cycle of Messor structor follows the standard egg-larva-pupa-adult progression. Because they belong to the Myrmicinae subfamily, they do not spin cocoons; their pupae are "naked" and can be seen clearly in the nest. Development time is typically 6 to 10 weeks, depending on the temperature. The presence of multiple queens can lead to a very high rate of egg production, resulting in a rapidly growing colony.

Nuptial flights for M. structor usually occur in the spring or early summer. However, they are also known for "nest splitting" or budding, where a queen and a group of workers leave an established nest to start a new colony nearby. This strategy is common in polygynous species and contributes to their success in colonizing large areas of suitable habitat.

Environmental Requirements

Messor structor requires a warm and relatively dry environment. The nest should have a temperature gradient, with a warm area around 25-28°C (77-82°F) and a cooler area. It is vital to provide both a "dry" section for seed storage and a "humid" section for the queen and the brood. If seeds are kept in a humid area, they will sprout or mold, which can be disastrous for the colony. Humidity in the brood chambers should be around 50-60%.

Like many temperate species, they require a period of diapause during the winter. From November to March, the temperature should be lowered to around 10-15°C (50-59°F). During this time, the ants will be less active and will rely on their stored seed reserves. Providing a proper hibernation period is essential for the long-term health and fertility of the queens.

Keeping Messor structor as Pets

Messor structor is an excellent choice for both beginners and experienced ant keepers. They are hardy, fascinating to observe, and their seed-harvesting behavior is unique among common pet ants. Because they do not require constant liquid sugar feeding, they are slightly lower maintenance than some other species. Their polymorphism and the bustling activity of a large, multi-queen colony make them one of the most rewarding species to keep in a home formicarium.

Recommended Habitats

For a successful harvester ant colony, specialized housing is key. We recommend the following ANT SHACK products:

• Ant Habitat Kit „Harvester Ants“ - This kit is specifically designed for the needs of Messor species. It includes the necessary substrate and a nest design that allows for the creation of both dry seed chambers and humid brood areas.
• Natural Ant Habitat Kit - Large - For a large, polygynous colony, space is essential. This kit provides a massive volume for the ants to explore and store their grain, allowing for a truly naturalistic harvester ant experience.
• All-in-One Desktop Ant Habitat - A great option for smaller, developing colonies. The easy-access outworld makes it simple to provide a variety of seeds and protein, while the secure acrylic nest keeps the colony safe and visible.