St Mark’s Fly – The Bringer of Spring (and Blossom)
Meet the St Mark’s Fly (Bibio marci), affectionately (or not!) known as the “dangle fly” thanks to its long legs that seem to hang loosely beneath it as it flies.
Why “St Mark’s” Fly?
These insects are named after St Mark's Day, because they typically emerge right around 25th April — almost like clockwork. Nature’s calendar at work. This year earlier because of climate change? Although the females hatch before the maLES.
What Are They Doing?
Those swarms aren’t random chaos — they’re actually mating gatherings.
- Males hover in groups, waiting for females
- Females fly into the swarm briefly
- Nature takes its course… efficiently!
After mating, females lay eggs in the soil. The larvae then get to work underground.
The Gardeners (You Didn’t Know You Had)
While the adults might seem a bit of a nuisance, their larvae are surprisingly useful:
- They feed on decaying organic matter
- Help break down soil nutrients
- Improve soil structure
In other words, they’re part of your garden’s invisible workforce.
Pollination Helpers
Adults often visit flowers — especially spring blossom — feeding on nectar. In doing so, they contribute (quietly and accidentally) to pollination.
Not quite as glamorous as bees… but still doing their bit.
A Slightly Awkward Flyer
If you watch them closely, St Mark’s flies don’t exactly glide like swallows. They:
- Fly slowly
- Drift about unpredictably
- Occasionally bump into you
They’re harmless — just a bit… enthusiastic.
The St Mark’s fly is one of those wonderful seasonal markers. Like daffodils, lambs in fields, or the first day you don’t need a coat, their arrival quietly signals:
Spring is here. Life is waking up again.
And next time you walk through one of those hovering swarms… just remember:
You’re not being attacked — you’re walking through a mid-air singles bar.
But it wasn't the only fly in the Garden so out came ...
The Garden Detective
“and the Case of the Not-So-Mark’s Fly”
It started, as these things often do, with confidence.
“There it is,as I showed if to my wife” I said, camera in hand.
“A St Mark’s Fly. Spring has arrived. Job done.”
Except…this one wasn’t.
The First Clue
On closer inspection, this “St Mark’s Fly” looked… wrong.
- Too slim
- Too yellow
- Not nearly hairy enough
- And standing there like it owned the flowerpot
Not the chunky, slightly bumbling insect I was expecting.
The Investigation
Out came the mental checklist (and a few photos):
- Size? About 1 cm
- Colour? Golden-yellow
- Legs? Long and purposeful
- Habitat? Plant pot, damp soil, organic matter
This was no casual visitor.
This was a professional.
The Reveal
The culprit is:
👉 Scathophaga stercoraria
Otherwise known as the yellow dung fly.
Not the most glamorous name…
…but far more interesting than it sounds.
What’s It Doing in My Garden?
Despite the name, it’s not just hanging around dung.
These flies:
- Patrol soil, compost, and vegetation
- Act as predators of smaller insects
- Are part of the garden’s natural pest control team
In other words…
It’s one of the good guys
A Case of Mistaken Identity
So what happened?
I saw:
- A spring fly
- Roughly the right size
- Sitting in the garden
…and jumped to conclusions.
Classic.
The Lesson
Not everything buzzing about in April is a St Mark’s fly.
Some are:
- Quiet hunters
- Garden helpers
- And far more interesting than they first appear
Final Thoughts
The garden is full of these little mysteries.
You think you’re photographing one thing…
…and end up discovering something entirely different.
And that’s half the fun.
Garden Detective verdict:
Case closed… but the investigation continues.
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