The most commonly talked about predator of greenfly is ladybirds, you can buy them online, or collect them from around the garden, often on stinging nettles, which are themselves riddled with greenfly.
Just as effective, and just as common, if not more so, are hoverflies. The flies themselves usually feed off of plant nectar, but the larvae of many hoverfly species feed on greenfly along with other aphids, thrips and any other small insect they can get their teeth into.
I have a few more greenfly than usual in the greenhouse this year, but today I noticed that the battle has turned against them. I have left the doors wide open in the last few days in the hope that some predators might come in, even at night, which means I risk moths coming in, and that means caterpillars. Sometimes the line between good and bad is a fine one.
I discovered a new way of finding greenfly, just watch where the hover flies go. I have never watched them this closely before.
Update – For a bit more on greenfly detection have a look at this later blog entry.
This chappy (chappess actually) hovered around the plants from shoot to shoot, only stopping at the ones which had greenfly in the tips.Here you can see her sucking on a leaf, maybe one that is covered with the sweet sticky dew that the greenfly exude, this is also the stuff that ants love. I couldn’t get a picture of her next move, which was to reach in with her back end and lay an egg among the greenfly. One egg laid, then on to the next shoot. Only the shoots with a greenfly benefited from an egg, so hopefully in a day or two a tiny larvae will emerge on each and start munching. They grow quite quickly so in a few days I will have a picture of one. Watch this space.