The Red Imported Fire Ant, Solenopsis invicta, is a highly successful and widely recognized pest species, notorious for its aggressive behavior and painful sting. Originating in South America, this ant has spread globally, establishing dense colonies in many regions. Their success is largely due to their extremely flexible, opportunistic omnivorous diet, allowing them to exploit virtually any available food source in their environment.
Common Scavenged Foods
The ants are highly opportunistic foragers, regularly consuming non-living or easily accessible food items found near their mounds. They demonstrate a strong preference for lipids (fats and oils) over carbohydrates, a trait often exploited in ant baits. Foraging workers quickly locate carrion, such as dead insects, spiders, and small deceased vertebrates, which provide the colony with necessary protein and fat.
They are particularly attracted to oily human food scraps and pet foods. Their food preferences can shift seasonally; carbohydrate sources like sugar baits are preferred during colder periods when other food is scarce. The ants generally avoid dry foods, preferring those with a minimum amount of liquid content.
Active Hunting Strategies
Beyond scavenging, S. invicta is a formidable predator that actively hunts and subdues live prey through coordinated effort. Worker ants use a powerful venom, composed mainly of piperidine alkaloids, to paralyze and kill their victims. This venom is used both as a defense mechanism and as a tool for securing food.
Their prey includes a wide range of arthropods, such as other ant species, insect larvae, ticks, and spiders. Working together, the ants can also overcome small, weak vertebrates, including bird nestlings and reptile hatchlings, which are quickly immobilized by multiple, coordinated stings. This collective hunting strategy allows a colony to bring down prey many times the size of an individual worker, providing a substantial protein resource for the growing brood.
Plant and Seed Consumption
The red imported fire ant incorporates significant plant-based material into its diet. They consume various seeds, particularly those with a fatty appendage called an elaiosome. The ants pose a risk to agriculture by feeding on planted field crop seeds, such as corn, wheat, and sorghum, before they can germinate.
Beyond seeds, the ants can damage living plants by girdling young stems or feeding on tender new shoots and buds. They also consume sugary plant exudates and honeydew, a sweet liquid secreted by sap-sucking insects like aphids. This consumption of carbohydrates helps sustain the adult workers, whose primary energy needs differ from the developing larvae.
Internal Distribution of Food Resources
The way a colony processes and shares food is highly specialized, relying on distinct physiological roles within the nest. Adult worker ants are only capable of ingesting liquids; they cannot directly digest solid food particles. Liquid food—such as oils, nectar, or dissolved proteins—is consumed by foragers and stored in their social stomach (crop) for later transfer.
This liquid is shared throughout the colony via a process called trophallaxis, where one ant regurgitates food for another ant, the queen, or young larvae. Solid food, like insect parts, must be carried back and given to the oldest larvae (the fourth instar stage). These larvae secrete digestive enzymes onto the solid material, liquefying the protein and fat externally so it can be consumed and then regurgitated back to the adult workers as a nutritious liquid.