The red imported fire ant, Solenopsis invicta, is a well-known species recognized for its aggressive nature and painful sting. Originating from South America, these ants have successfully spread across various regions globally, including parts of the United States, Australia, and Asia. The queen ant serves as the central figure in their colonies, playing an important role in their establishment, growth, and persistence. Understanding the queen’s biology is therefore important to comprehending the overall dynamics of these ants.
Identifying the Queen
Distinguishing the Solenopsis invicta queen from other ants in a colony involves observing several physical characteristics. Queens are noticeably larger than worker ants, measuring 6 to 8 millimeters in length, whereas workers range from 2.4 to 6 millimeters. Their coloration is reddish-brown.
A defining feature for a mature queen is the presence of wing scars on her thorax. Before mating, queens have wings for their nuptial flight, but they shed these wings afterward, leaving visible remnants. The queen’s head is oblong, lacking a median indentation along the occipital border. Her overall body proportions, including the head, mesosoma, and gaster, are more robust compared to worker ants.
Establishing a New Colony
Establishing a new Solenopsis invicta colony begins with a nuptial flight, which occurs during warmer months. During this flight, winged male and female reproductives mate in the air. After mating, the queen descends to the ground and sheds her wings, marking the start of colony founding.
The queen then seeks a suitable nesting site, often in disturbed soils or open areas. She constructs a small burrow, a vertical tunnel about 7 cm deep with a cell at each end, and seals the entrance. Within this sealed chamber, the queen begins to lay her first batch of eggs within 2 to 3 days post-flight. She relies on her stored fat reserves and wing muscle proteins for nourishment during this initial period, as she does not forage for food. These eggs develop into larvae in 6 to 8 days, then pupae in 14 to 15 days, with the first worker ants emerging in 20 to 24 days.
The Queen’s Ongoing Role
Once the first generation of worker ants emerges, the queen’s role shifts to primarily egg-laying, as the workers take over foraging and brood care. The queen is the sole egg layer in a colony, producing most new individuals. A single queen can live for up to seven years and lay from 800 to 5,000 eggs daily in mature colonies.
Her reproductive output ensures the continuous growth and maintenance of the colony, which can range from a few hundred to over 500,000 individuals. Queen pheromones play a role in regulating colony behavior, influencing worker tasks, and guiding the development of different castes within the colony. While many S. invicta colonies are monogyne (single queen), some can be polygyne (multiple queens), with up to two thousand reproductive queens, which can lead to larger colonies and a different spread pattern, sometimes through budding.
Why the Queen Matters for Control
The Solenopsis invicta queen is the primary target in control efforts because the long-term survival of a fire ant colony hinges on her reproductive capacity. A colony cannot sustain itself without a queen continuously laying eggs to replenish the worker population, as worker ants live for only several months. Eliminating the queen directly disrupts the colony’s ability to reproduce and grow, eventually leading to its decline.
Successful control strategies often focus on methods that specifically target the queen or severely impair her reproductive function. This can involve baits that workers carry back to the nest, which the queen then ingests, or direct treatments to the mound designed to reach her. The invasive nature of S. invicta and its widespread distribution, particularly in the southern United States, is largely due to the queen’s high reproductive rate and her ability to establish new colonies, sometimes dispersing a kilometer or more. These ants cause economic damage to agriculture and can negatively impact native ecosystems, highlighting the need for queen-focused control measures.