Thousands of aphids have suddenly appeared in Oxfordshire. I can squish them, blast them with a jet of water from the hose or spray them. I don’t like spraying because it harms the beneficial insects as well as the pests, so generally squish or blast. As luck would have it, this year the predators have arrived at roughly the same time as the aphids and are saving me having to do much myself. They have come in the form of ladybird larvae. These are about 1cm long, though smaller when young, and have dark grey, segmented bodies with some orange spots down each side. They don’t look like ladybirds at all and can be seen in such large numbers that they could easily be mistaken for a pest themselves.
Along with ladybird larvae, the larvae of hoverflies and lacewings will also eat aphids. During a ladybird’s year of life, it can eat up to 5,000 aphids which makes them a welcome guest. Several parasitic wasps kill aphids, too, by laying their eggs in the aphids themselves. Looking at the underside of leaves affected by aphids, you may see a tiny, bloated, slightly metallic insect which never moves. This unfortunate creature has had an egg laid in its body by a parasitic wasp. Get a magnifying glass and keep an eye on it; in a couple of weeks, the new wasp will chew its way out, in a similar way to the monsters in the film ‘Alien’. I’ve wondered if that’s where they got the idea for that film, actually.
Aphids are a real pest, sucking the sap from plants and excreting sticky honeydew, with the result that the plant can be seriously weakened and, if not killed, the plants may be very distorted and bear few flowers or little fruit. They seem to appear almost overnight; one day the plants are fine and the next thing you know, stems and flowers are a mass of tiny, twitching green, brown or black insects. The reason they increase so fast is that they reproduce by parthenogenesis, meaning that they are born pregnant. When I was a student we were told that just one aphid, if left to reproduce without being eaten by a predator, would produce 10 million tons of new aphids within 100 days. Scary thought and it’s something I’ve never forgotten.
Quick update on the wasps
They are still building and I managed to get a couple of better photographs of the guard wasps on the outside of the shed.
A male common wasp
Common wasp, worker caste
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