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I think the lid is perhaps not tight-fitting enough to keep out the egg-laying females.  any suggestions on how i can kill the larvae?  I need to be able to use the water for plants.   i have to scoop water out from the top, as the butt is set too low to allow a tap in the bottom.  i've read that a layer of oil or soap on the top would prevent the larvae from breathing, but i don't think that will be too good for my plants.  


I,ve used cooking oil and it does work. It forms a film over the top.It won,t harm your plants because the oil is plant based. And you don,t need oodles either. It.s certainly been the year for the moscito

thanks for the quick reply!  how much cooking oil do you put in?  mine is a 200 litre butt, and quite wide at the top.  do you need to have a film of oil completely covering the surface, or just enough to have some slicks floating around?  


Bob Flowerdew keeps a goldfish in his to eat the larvae!


Hi, veg oil acts as a barrier and stops the larvae from breathing through tubes when they go to the surface, it doesn't have to be thick but for best results cover the hole surface area, as it acts on the surface most can be syphoned off if your dubious about leaving it in,


Gardening Grandma

You can also add polystyrene beads, which help prevent the mosquito laying eggs in the water. If the water is used regularly, so that the water is constantly changed, there isn't much problem because mosquitoes like stagnant water, but in wet weather such as we are having at the moment, the water in the butt can be undisturbed for quite a time. So it might be an idea to empty the butt and start again. 


I add a teaspoon of a bee friendly insecticide to a 40 gallon water butt, kills off the larva and is so minute in concentration it does no harm when I water things with it.

Just a teaspoon of vegetable oil in each butt will do the trick.


Hi Rosa Rugosa, sorry i didn,t get back to you. However the replies you,ve received tell you all asked. I,m battling snails who are decimating my dahlias. It seems Pests 10 Gardeners nil this year! I like a challenge but really. Wellies in July.......

Paul N

I have four water butts, none of which are covered, and have been like that for about 25yrs. Yes there's larvae in there but I can't say it bothers me. Perhaps we use the water more frequently. They are also up off the ground so I can fill the watering cans.

thanks all, for the useful advice.  i will try the oil first.  we have mega mossies here.  they have such an itchy bite, or maybe it's just how i react to them.  the itch lasts for weeks.  the fish idea is cute too!   i'd have to leave the lid off though, and then you get all the algae and stuff.......  we did have some goldfish in the pond, and  i never saw a mossie larva there.  we have lots of dragon fly nymphs, and i think they do the job too.    

about snails - i used ferrous-based slug pellets around all the plants that are particularly precious to me, at least until they are large enough to take a bit of snail pruning.  and now i go around every evening, and spear the slugs with sharp sticks, which i then chuck in the compost.  i never used to be so merciless until i got my first lupins and clematis!  


I tried the oil thing, but I found it covered the watering can when I dipped it in the water and made it very slippy.

yes that's what i fear too, but i'll try it.  don't really want to expose myself and kids to insecticide unnecessarily, so that will be my last option.  what about dishwashing liquid?  a teaspoon in a small sprayer definitely kills aphids.  i wonder if it would work on mossie larvae?  

Mosquitoes only bite certain people, so perhaps Paul you are one of those who have a chemical in your perspiration that deters them.    I react badly to bites - they seem to love me!   

Only use oil if you use a tap at the bottom of the butt.    The oil is supposed to sit on the water at the top - no good if you have to take your water out that way.


oh i used to be one of those people that got bit by anything and everything.. nightmre as half garden is shaded and gets lots of little biting insect... but since i hve been taking garlic and vitaminb caps.. i dont get bitten. so lovely to be out and not end up covered in bites by end of the night.

oh and great info on the butts problems.. i have added oil to mine to day and will see how it goes.



Hi rosa, the oil trick works. you only need a little bit.attach a piece of hosepipe to the water butt tap to fill your can, it will stop the can being messed up with the oil.

how cruel of flowerdew to put a poor gold fish in the butt. my goldfish love the light.the thought of livinging in the dark till it die(i liked him too!!)

i can definitively say that dishwashing liquid in a water butt, a lot of it, does not kill mosquito larvae.  i suppose you would not put a lid on the water butt if you kept a goldfish in it.  but i wonder how happy it would be?  well, why not, if you make it cosy!  but i will try the oil next.  thanks for all the tips!  

As well as adding oil I tie a thick cloth (old towel etc)sprinkled with a little Deet  Mosquito killer (optional) round the pipe and over the hole in the lid.  This stops them getting in in the first place.

Learn from my mistake & PLEASE dont do what i did.

I put oil on the water but left the lid off. I really, really, hate myself because a green tit had tried to drink from the butt and drowned!!! (yes, i am ashamed at my stupidity)

Stacey Docherty

Oh dear Paul it's nothing we haven't all done tho! I had an old bathroom bin that I used to use and after last winter found a dead squirrel in it!!!! Oil is what I use as well and we suffer badly from it here... But I love the idea of having a goldfish in it lmao