Water butts and hoverflies

Posted: Friday 25 July 2014
by Kate Bradbury

There has been a lot of talk about mosquitoes lately, not least the suggestion that stagnant water in water butts is increasing urban populations of mosquitoes.

There has been a lot of talk about mosquitoes lately, not least the suggestion that stagnant water in water butts is increasing urban populations of mosquitoes. (My favourite headline: ‘Could trendy water butts cause malaria?’)

Reports cited research conducted at the University of Reading, which suggests that water butts provide the perfect breeding ground for mosquitoes. I’m sure any water-conscious gardener can confirm this, and I’ve known people add olive oil and even goldfish to their water butts to keep mosquito numbers down.

There’s no hope of me avoiding insect bites on the allotment. Around my plot alone there are more than 10 open troughs, butts and other vessels brim-full of stagnant water and wriggling mosquito larvae. But, for me, a few bites are worth it to see another stalwart of the allotment water butt: my favourite hoverfly, Myathropa florea (pictured above, click to enlarge).

Myathropa florea doesn’t have a common name, but I think its scientific name has a lovely ring to it. It’s a gorgeous, stout hoverfly with bright yellow and black bars, and a lovely deep buzz. Unlike many hoverflies, which breed on plants infested with aphids, Myathropa florea lays eggs in stagnant water – typically in rot holes and ditches – but I’ve also seen females lay eggs in damp compost heaps and Bugman Jones once found one laying in his kitchen drain.

A buzzing alerted me to one on the allotment the other day, which was investigating the water in a butt close to where I was weeding. I watched it dart back and forth, appearing to almost dip its head in the water, before allowing me to photograph it while it stopped to take a closer look (or so it seemed). I assume it was a female looking for somewhere to lay eggs, although no egg-laying was witnessed on this occasion.

Of course, the larvae of this beautiful hoverfly is the unflatteringly named rat-tailed maggot. I happen to love rat-tailed maggots, especially when they get really big. But lots of gardeners are put off by their maggot-like form. The ‘tail’ is actually a breathing tube; I don’t know if that makes them more or less alluring. But the adults are pretty, and there are plenty of both in a water butt near you, along with millions and millions of wriggling mosquito larvae.

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Talkback: Water butts and hoverflies
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MrsDeapSleap 25/07/2014 at 22:09

Surely if your water butt has a lid on it, mosquitoes can't take up residence and breed? My house has a water meter, so a water butt in the garden is an essential!

greg 4 25/07/2014 at 22:14

I have one of those 210 litre green garden water butts. It's linked to automatically top up my mini pond. It has a cover and there are no mosquitos in it. I have another 2 butts just 20 feet away and they're rife with mosquito larvae.

Daintiness 25/07/2014 at 22:19

Bob Flowerdew keeps  goldfish in his water butts to eat the larvae.

artjak 26/07/2014 at 07:02

When I worked in Barbados, a local Nursery owner told me they never had saucers under their plant pots as we do here as any standing water would encourage mosquitoes. I can't understand why a lidded water butt would have mossys. Greg, are the other 2 butts with lids?

oldchippy 26/07/2014 at 12:12

My daughter had mosquitoes in her water butts with lids on ,the man next door had a large pond the fish in it and froglets he said put some froglets on the lid and see if they clear them, and it worked as they could get in the down pipe hole in the lid.

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