A rat-tailed maggot is the larval stage of the drone fly (Eristalis tenax), a common fly that mimics the appearance of a honeybee. The name comes from a long, retractable breathing tube that extends from the maggot’s rear end, giving it a distinctive tail-like appearance. These larvae live in stagnant, heavily polluted water and feed on decaying organic matter. Despite their unpleasant habitat, they grow into beneficial pollinators.
Why It Has a “Rat Tail”
The so-called tail is actually a telescoping breathing tube, technically a posterior spiracle. It works like a snorkel: the maggot sits at the bottom of shallow, murky water while extending this tube up to the surface to draw in air. The tube can stretch to two or three times the length of the maggot’s body, reaching over 20 centimeters (about 8 inches) in some cases. This adaptation lets the larvae thrive in water so oxygen-poor that most other insects can’t survive there.
The maggot itself is roughly three-quarters of an inch long, whitish or grayish, and soft-bodied. Without the tail, it looks like a typical fly larva. With the tail fully extended, it’s unmistakable and unlike any other common insect larva you’re likely to encounter.
Where They Live
Rat-tailed maggots are found in shallow water with high concentrations of organic waste. Sewage lagoons, stagnant pools, drainage ditches, manure pits, and water troughs with decaying vegetation are all prime habitat. They feed on the decaying material in these environments, helping to break it down. If you’ve found one, it almost certainly came from a nearby source of standing, nutrient-rich water.
They’re not picky about geography. The drone fly was introduced to North America from Europe around 1875 and has since spread widely. You can find rat-tailed maggots across much of the world, wherever conditions are wet and organic matter is accumulating.
Life Cycle: From Maggot to Bee Mimic
Female drone flies lay eggs on or near the surface of stagnant water. The eggs hatch in two to three days, and the tiny larvae begin feeding on decaying matter at the bottom. Larval development time varies depending on conditions like temperature and food quality, but adding nutrient-rich material to the water shortens development time. Once fully grown, the larvae leave the water and find a dry spot nearby to pupate. The pupal stage lasts six to nine days before the adult fly emerges.
The adult drone fly looks remarkably like a honeybee, with similar striping patterns and body shape. Eristalis tenax can fool even trained scientists when it flies past. It doesn’t just look like a bee; it has adapted its flight behavior to move back and forth between flowers rather than hovering in place the way most flies do. This mimicry is purely defensive. Drone flies have no stinger and are completely harmless.
As adults, drone flies are active pollinators. They visit a wide variety of flowers from early spring through late fall, feeding on nectar and absorbing pollen grains. Females need the extra protein from pollen to produce eggs. Because they have several generations per year, they provide pollination services across multiple seasons, switching between different flower types as blooms come and go.
Can They Infest Humans?
Rarely, yes. Rat-tailed maggots can cause a condition called intestinal myiasis when someone accidentally swallows larvae or eggs in contaminated, uncooked food or untreated water. In even rarer cases, larvae can enter through the rectum. This is not a common health concern, but documented cases do exist in the medical literature.
Symptoms vary widely. Some people have no symptoms at all and only discover the infestation when they notice larvae in their stool. Others experience abdominal pain, nausea, vomiting, diarrhea, or anal itching. In one published case, a patient had abdominal pain and pasty diarrhea lasting three weeks, with symptoms resembling an inflammatory bowel condition. The key point is that the larvae don’t establish a permanent infection. They undergo partial development inside the digestive tract and are eventually expelled on their own.
Diagnosis is straightforward: larvae are visible in stool samples, either with the naked eye or under a microscope. Treatment typically resolves the issue quickly, and the condition is considered benign in most cases.
How to Tell Them Apart From Other Larvae
The breathing tube is the giveaway. No other common aquatic larva in household settings has a long, extendable tail. Moth fly larvae (the small fuzzy flies you sometimes see near drains) are also found in wet, organic-rich environments, but they lack the distinctive siphon and are much smaller. Regular fly maggots are similarly sized but have no tail structure at all.
If you find a whitish larva with a visible tail in or near standing water, a compost bin, or a neglected drain, you’re almost certainly looking at a rat-tailed maggot.
Getting Rid of Them
Rat-tailed maggots are a symptom, not the core problem. They show up because stagnant, organic-rich water is available nearby. Eliminating their habitat is the most effective approach: drain standing water, clean out water troughs, clear clogged drains, and remove accumulations of decaying plant material. Without a suitable breeding site, adult drone flies will lay their eggs elsewhere.
If you find them in a compost pile or rain barrel, increasing drainage or covering the water source prevents adult flies from accessing it. In most cases, these maggots are more of a nuisance than a threat. The adults they become are genuinely useful pollinators, so unless they’re appearing in large numbers in a problematic location, they’re doing more good than harm in the broader ecosystem.