Flies do not typically “eat” ants in the way a bird eats a worm, but a specialized subset of flies actively targets and consumes ants across various life stages. The relationship is complex, encompassing parasitism of live adults, predation on ant young, and simple scavenging of remains. For most fly species, ants are merely an obstacle, but for certain groups, the ant colony represents a unique and highly specific food source.
Specialized Flies That Parasitize Live Ants
The most dramatic interaction involves parasitic flies in the genus Pseudacteon, commonly known as ant-decapitating flies (Phoridae family). The female fly initiates the process by hovering over a foraging worker ant and injecting a single egg into the ant’s thorax using a specialized ovipositor. This effectively turns the live ant into a living incubator.
Once the egg hatches, the larva begins to develop within the ant’s body, consuming internal tissues. The maggot then migrates into the ant’s head capsule, where it feeds on the brain and muscle tissue. When fully grown, the larva releases an enzyme that dissolves the membrane holding the ant’s head to its body, causing the head to fall off.
The maggot uses the detached head as a protective case, or puparium, inside which it pupates. After two to six weeks, the adult fly emerges from the ant’s head capsule. This specific parasitism is a major factor for certain ant species, such as imported fire ants.
Larval Predation on Ant Nests and Brood
Other fly species have larvae that specialize in feeding on the ant colony’s immobile young, collectively known as the ant brood. These larvae often infiltrate the nest to prey on the soft-bodied eggs, larvae, and pupae, which are rich sources of protein. Certain species of hoverflies, such as Microdon flies, are known as “ant-lovers” (myrmecophiles) because their larvae grow up directly inside ant nests.
These fly larvae may mimic the ant’s own cocoons to avoid detection or might be tolerated by the adult ants. Older Microdon larvae actively consume the ant larvae by piercing the skin and emptying the body contents. Scuttle flies from the genus Apocephalus may harass worker ants carrying brood during an evacuation, causing the workers to drop the young so the fly can lay an egg into the exposed larva.
Some fruit fly larvae, such as those in the genus Rhinoleucophenga, employ a unique predatory strategy by taking advantage of ant-plant mutualisms. These flies lay eggs near plant nectaries where ants forage for sugar, and the resulting larvae ambush and consume the patrolling ants.
Scavenging and Indirect Consumption of Ant Materials
Flies interact with ants through less aggressive means, primarily by scavenging on dead ants or consuming resources associated with the colony. Common flies, including house flies and flesh flies, feed on dead ant workers, treating them as a source of carrion or decaying organic matter. This passive consumption is an important part of nature’s recycling process.
Flies are also attracted to materials produced or gathered by ants, leading to indirect consumption of ant-related substances. For instance, flies may feed on the honeydew secreted by aphids that ants “farm” for their sugary excretions. They can also be found consuming food scraps or waste that ants deposit in designated refuse piles outside the main nest chambers. This behavior is opportunistic and contrasts with active predation.
The Role of Flies in Ant Population Control
The specialized feeding habits of ant-attacking flies give them a significant role in regulating ant populations within their ecosystems. Decapitating flies, particularly Pseudacteon species, are highly host-specific, often targeting only a single species or size class of ant worker. This specialization makes them effective biological control agents, especially against invasive species like the red imported fire ant (Solenopsis invicta).
The presence of these parasitic flies can drastically disrupt the host ant’s behavior. Fire ants reduce their foraging activity and focus on defensive posturing to avoid aerial attacks, which starves the colony of resources. This harassment shifts the competitive balance, allowing native ant species to better compete for food and territory.
Multiple species of these flies are often used together in biological control programs because different species attack different sizes of ants or at different times of day. This multi-pronged attack strategy is necessary to achieve a broader effect on the ant colony’s overall health and foraging efficiency. The flies exert co-evolutionary pressure, leading to defense behaviors in ants that slow their growth.