If you’ve ever seen what looks like a severed rat’s tail writhing around inside a pond or a moldy tree, chances are you’ve spotted a rat tailed maggot. Rat tailed maggots are the larval form of some species of hoverfly, which can be terrestrial or aquatic. They start out life as a blob with a breathing tube, later dragging themselves onto land to pupate and turn into certain flies.
We asked entomology expert and museum curator Dr Erica McAlister of the London Natural History Museum about the curious life cycle of the rat tailed maggot, and the epic transformation they undergo to metamorphose into their considerably more athletic adult form.
What is a rat tailed maggot?
“Rat tailed maggots are the larval stage of many species of hoverfly (Syrphidae) in the tribes Eristalini,” McAlister told IFLScience. “The maggots are most commonly found in dank and decaying environments such as your compost, the margins of ponds and also in tree rot holes where they feast on the decomposing material which is oxygen poor but organic rich.”
Dank and decaying is about right, as rat tailed maggots were once found gorging on a different kind of organic matter around the drop toilets at Glastonbury Festival, Somerset, UK. Mind you, like these eels, they might’ve ingested a little more than feces.
Okay, but what about that tail?
The “tail” that the rat tailed maggot appears to drag around is actually used for respiration, even though it’s attached to the maggot’s butt.
“The siphon (the ‘tail’) is their breathing tube to enable them to breathe external of the substrate in which they are feeding (I affectionately call them bum breathers),” said McAlister. “Although the siphon is usually just the length of their bodies, they can be extended hugely with some reaching to 15 centimeters (6 inches) while the mature larvae is between 1 and 2 centimeters (0.4 and 0.8 inches).”
What does a rat tailed maggot turn into?
Rat tailed maggots are the larval form for several species, so it depends on who laid them as an egg. Like all flies, says McAlister, they’ll undergo complete metamorphosis from an egg to their adult form – but first, they emerge as larvae.
“This is an incredibly important stage for them as they lay down reserves for their adult stage, and for us because they recycle nutrients,” said McAlister. Next, they pupate.
“The pupal stage is arguably one of the most fascinating things in nature where the majority of the body’s tissues are reorganized. During the pupal stage they develop legs, wings, and genitalia – the essential structures for adulthood.”
“The adult stage is all about the flirt – with the males often territory guarding prime habitat that the females want to lay eggs in. But the adult is also an important stage, as they are nectar feeders and, as such, excellent pollinators.”
The rat tailed maggot can go on to become a range of hoverflies, including some you might expect for an animal with such a name (bog hoverflies) and some you might not (the batman hoverfly, Myathropa florea).
Are they safe?
Rat tailed maggots aren’t harmful – unless they get inside the body in something known as myiasis, an infection with fly larva which is seen across many species. This is more common in certain parts of the globe and can happen through ingesting eggs or fly larvae, or from having eggs hatch on the skin or near wounds after which the larvae burrow inwards.
So, if I see a rat tailed maggot wriggling across my pond or garden – what should I do?
Leave those babies well alone. While they might not be the most aesthetic in the insect world, they are champions for the environment, both as babies and as adults.
“Hoverflies are incredibly important in ecosystems for several reasons,” continued McAlister. “They are species rich and abundant, and both the adult and the larval stage are active. Within this family, the larva are not only recyclers but also predators, the majority of which are aphidophagous (feeding on aphids and their kin) which provides great ecosystem and agricultural services in keeping plant-feeding insects in check."
“The adults are pollinators and due to their abundance and ability to cope better in more extreme environments than many bees are very important ones. As well as this, many of the hover flies migrate long distances (such as across Europe, America and Australia) pollinating as they go.”
"This migration enables the spread of pollen across plant populations and so is very important for gene flow across the more isolated plant populations, as well as providing food for a wide range of predators including other migratory species. With 4 billion turning up annually on UK shores alone, the impact they have is formidable and hugely undervalued.”
So, if you see a rat tailed maggot, do your bit by simply letting it do its thing. If you see a severed rat’s tail on the other hand? Well, you’re on your own there.