Monday, 26 May 2014

A Stinking Comfrey Bath Full of Rat-tailed Maggots

Two of my previous posts have become unexpectedly linked. For it wasn't long ago that I encountered this creature in my polytunnel

This is a drone fly, so called because of its superficial resemblance to a honey bee. It appeared in my post about polytunnel intruders.

Now just outside the polytunnel sits this old bath, full of stinking comfrey juice.

It is just rainwater with a bag of comfrey leaves immersed, but this makes the water go really quite disgusting. It has a rather unappealing aroma too, though you get used to it. But it's worth it for the black gold it produces, free plant food which my tomatoes love. For more on growing and using comfrey, you can visit this post.

So you're probably wondering what these two subjects have to do with one another. Well my tomatoes are just forming their first fruits now so I decided yesterday to start feeding them but, as I approached the bath of black liquid, I could see what appeared to be hundred of slugs swimming around in it, slugs with tails! The last thing I would want to do is pour slugs, or anything similar, all over my crops.

So a quick internet search for "water larva spiky tail" brought me instantly to the answer at

The aquatic larvae of droneflies are known as Rat-tailed maggots.  They develop in stagnant water, animal faeces and rotting carcasses.  The more putrid and foul-smelling it is, the more the larvae seem to like it.
Each larva is equipped with an extendible tail called a 'siphon'.  This tail, which can extend to about 5cm (2 inches), is used as a snorkel to breath air from the surface of the liquid while the larva feeds below.

Special features:  Drone flies look similar to honeybees (hence the 'drone' name), but they lack the narrow waist between the thorax and abdomen.  They also have just two wings, where the honey bee has four.

The body is brown to black in color, quite hairy, with varying amounts of orange/yellow markings on the side of the second and third abdominal segments.

The males have large eyes which meet in the centre, while the females have smaller eyes with a gap in between.

When they are fully grown, the larvae leave the water to pupate.  The pupae are a reddish-brown colour.  At the front are some
horn-like projections, and the tail often curves up and over the back of the body.

Mystery solved.


  1. I had those in my comfrey tea last year... not had them before...

  2. Obviously they like comfrey then!

  3. That is very interesting. I had never heard of, or seen, a drone fly before. What did you do about the existing maggots in your comfrey bath? How have you prevented them from reappearing?

    I recently began studying herbalism and am beginning to experiment with comfrey. Found your post as a result of searching Google for information about comfrey bath. Wasn't expecting to find anything about flies and rat-tailed maggots, but it is good information to know ... for future reference. I won't be leaving any comfrey sitting out uncovered. :)


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