What on earth . . . and its tail is a snorkel!

By The Marine Detective on September 15, 2022

Here’s one of the best mysteries I’ve been gifted recently.

It started with videos sent to me from Leesa Flynn that she had taken at Cordova Bay, southern Vancouver Island, British Columbia. Just look! What powers of observation Leesa has. This animal is less than 6 cm long and what’s with that tail?!

I did NOT know what this animal was and how my interest was piqued. I did suspect it might be an organism found in non-marine environments since it was so high up in the intertidal zone. Likely the water was not very salty where it was found.

The mystery had to be solved
I am very fortunate to have quick access to expertise far greater than my own. Those I reached out to included Rick Harbo, author of many ID guides for marine life of the Pacific Northwest. Rick did not recognize this animal, so off the videos went further into the web of expertise, intriguing many biology experts along the way.

To the relief of all, the identification came back through Hugh MacIntosh of the Royal BC Museum and Kevin Kocot of the University of Alabama. They recognized that this was a larval stage of a species of Hover Fly. The larvae are not known to be in marine environments so the water near this organism must have been from a creek flowing on the beach or highly diluted by rain.

Larva of a bee-like insect
The long tail of these larvae functions like a snorkel. It’s a breathing tube whereby larvae of Hover Flies can be underwater feeding while breathing from the surface. What a remarkable adaptation!

There are MANY species of Hover Fly and they are really important to the environment. The adults are important pollinators and the larvae recycle nutrients and some feast on pests like aphids (which parasitize on plants / crops).

But what species of Hover Fly specifically was the larva that Leesa observed? I think this mystery organism is a species of Drone Fly of genus Eristalis. I provide detail about that at the end of this blog. First let me address . . . Rat-tailed Maggots.

Rat-tailed Maggots and Bum Breathers?
I learned that the broad grouping of larvae in the family of Hover Flies appears to be referenced as “Rat-tailed Maggots”.

There’s an increased chance that you’re cringing now – right? Many of us have negative associations with the words “maggot” and “rat”.

That wonderful adaptation of the long breathing tube allows these larvae to live and feed in environments that may poor water quality e.g. sewage. As described by Real Monstrosities: “Since Rat-tailed Maggots breathe air, they have no use for gills, which in turn means they’re not particularly reliant on water quality. Thus, there’s many a Rat-tailed Maggot that lives in the squalor of cesspits, pools of sewage, watery manure or carcasses.“

The one featured in this mystery is not likely to have been in water of poor water quality. It’s just that they could live and feed in those environments. They can also be terrestrial. They do tend to lay eggs in nutrient rich environments.

Here you have colourful text from IFLScience about this broad group of larvae to accompany the video above of a different species of Hover Fly larvae (not the species in this mystery).

“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. Rat tailed maggots enjoy feeding on decaying organic matter which is why you’ll often find them in dank ponds and rotting trees, as well as anywhere there’s an open source of feces (including, one time, Glastonbury Festival).

They have a long breathing tube called a siphon attached to their rear end which is why some entomologists affectionately refer to them as “bum breathers”. They bulk up in their larval, rat tailed maggot form before pupating in soil or other dry material and emerging as several species of hoverfly.

You might think the rat tailed maggot is a little ugly, but they are champions for the environment both in their larval and adult forms. As rat tailed maggots, they encourage the turnover of nutrients by eating decaying matter and pooping it out again. They also predate on common plant pests such as aphids.

As adults, they’re hugely important pollinators which facilitate gene flow across isolate plant populations as they are big travelers. So, if you see a rat tailed maggot, do your bit by simply letting it do its thing.”

But which larvae is this specifically?
I think that the larva in this mystery is a species in a subgrouping of Hover Flies (family Syrphidae), known as Drone Flies (genus Eristalis).

In what I was able to learn from the contributions to iNaturalist.ca, it appears there are 6 species of Drone Fly that have been found on Vancouver Island. I am hopeful that an etymologist reading this blog will be able to narrow down which one this larvae is.

The six are:
Common Drone Fly – Eristalis tenax
Dusky Drone Fly – Eristalis obscura
Orange-legged Drone Fly – Eristalis flavipes
Orange-spotted Drone Fly – Eristalis anthophorina
Orange-spined Drone Fly – Eristalis nemorum

Thank you so much for your interest in all creatures great and small, furred and maybe what some human brains interpret as a little freaky. These species are perfection with adaptations that ensure success in the web of life. A web to which we, of course, belong. 💙

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Sources:

• BugGuide – Eristaline larvae
• IFLScience – What Does A Rat Tailed Maggot Turn Into?
• iNaturalist.ca
• Thyselius, M. (2022). A behavioural investigation into Eristalis tenax : Pursuit, approach estimation, locomotor activity and rearing (PhD dissertation, Acta Universitatis Upsaliensis)
• A Parasitologist’s View of the World – Case 449 Answer: rat-tailed maggot, family Syrphidae

Above: Comic by UnderdoneComics.com which included the text: “Ever spend time outside and notice an insect that looks like a bee but has wings like a fly hovering near you? Well sir, that’s a hoverfly. And my favorite kind is the drone fly—because, as you can see from the comic—it has an amazing lifecycle.

Before they become bee-lookalikes, their larval stage resembles a deep sea diver. They breathe through a tube that comes out of their butt and they laze around eating plant particles. How crazy is that?”