My neighbour's water-tank, which he uses to irrigate his potager, is brimming with mosquito larvae. His tank is about 20 metres from the sitting-out-and-eating bit of our garden. Soon they will all hatch out. They won't bother him, because his house is much further away, and anyway, he doesn't use his garden other than for growing his veg. Someone told me that pouring oil on the top of the water will prevent the larvae from breathing, and yesterday I poured some sunflower oil on. The larvae didn't seem to be able to penetrate my little oil slick, and they surfaced elsewhere in the tank. The thing is, I can't cover the whole tank in oil, he would be bound to notice; I get on well with him and don't want to upset him. I have thought of scooping them out with a child's fishing net, but I don't think the holes would be small enough. What else can I do? Buy some goldfish? Is there anything else that would eat them? What to do?