The red harvester ant, scientifically known as Pogonomyrmex barbatus, is a prominent insect species known for its industrious behavior in North America’s arid and semi-arid landscapes. These ants are a common sight across the southwestern United States and Mexico, thriving in dry conditions. Their presence significantly shapes the ecosystems they inhabit, making them a subject of considerable interest in desert ecology.
Appearance and Habitat
Red harvester ant workers typically measure between 0.6 to 1.3 centimeters (1/4 to 1/2 inch) in length and display a reddish to dark brown coloration. A distinguishing feature is the psammophore, a row of hairs on the underside of their heads, which aids in carrying soil and other particles. These ants are found across a wide geographical range, including grasslands and deserts of the southwestern U.S., extending from Kansas and Oklahoma through western Texas, New Mexico, and Arizona, and into Mexico.
Their nests are large, circular clearings devoid of vegetation, making their colonies easily identifiable in open landscapes. These mounds, which can range from 0.9 to 10.7 meters (3 to 35 feet) in diameter, often have a single entry hole. The ants remove plants around the nest to allow sunlight to keep the area warm and dry.
Seed Harvesting and Diet
Red harvester ants are primarily granivores, meaning their diet consists mainly of seeds. Their foraging activities are highly organized, with nest patrollers assessing the safety and profitability of foraging grounds. Once conditions are suitable, foragers venture out, often traveling along distinct trunk trails that can extend up to 60 meters (200 feet) from the nest.
They collect a variety of seeds, including alfalfa, Johnson grass, oats, wheat, and wild sunflower. They use their large mandibles to grind collected seeds into a bread-like consistency, which is then stored in underground chambers called granaries. These granaries allow the colony to maintain a consistent food supply throughout the year, even during periods of scarcity. While seeds form the bulk of their diet, they also collect dead insects.
Colony Structure and Defense
A red harvester ant colony operates as a social unit, typically comprising a single queen and a large population of sterile female workers. The queen is responsible for reproduction, laying eggs that develop into new ants. Worker ants perform all other colony duties, including foraging, nest maintenance, and defense. An established colony can house around 10,000 ants, with queens potentially living for up to 30 years.
Red harvester ants are known for their defensive capabilities. They possess a powerful sting that can cause considerable pain, comparable to a bee sting, and the effects may spread along lymph channels in some cases. While their sting is venomous, they are generally not aggressive and typically only sting when their nest is directly threatened. Workers may also seal the nest entrance with gravel and twigs in the evenings to deter intruders.
Ecological Importance
Red harvester ants play a significant role in their ecosystems, contributing to environmental processes through their nesting and foraging behaviors. Their extensive underground tunnel systems, which can reach depths of 4.5 meters (15 feet) and contain numerous chambers, contribute to soil aeration. This tunneling improves soil structure and water infiltration.
These ants are also important agents of seed dispersal, a process known as myrmecochory. While collecting seeds for their granaries, some seeds are inevitably dropped or discarded, leading to their distribution across the landscape. This dispersal benefits various plant species by expanding their range and density. Red harvester ants serve as a primary food source for several predators, notably the Texas horned lizard, whose diet can consist of up to 90% of these ants. Their decline in some areas, often due to competition with invasive species like the red imported fire ant, can negatively impact populations of these predators.