Meet the aphid assassins

These tiny predators will chomp through masses of green and blackfly… Adrian Thomas sings their praises

The sight of aphids smothering a favourite plant is sure to strike annoyance in the heart of any gardener. When your fresh broad bean foliage gets smothered in black aphids or the buds of your roses become clad in massed green ones, you might well feel the urge to reach for the chemical sprays. But help is at hand – from an army of aphidmunchers who are eager to get to work. Before meeting your knights in shining armour, it’s good to understand your enemy. You probably know that aphids are insects, but did you know there are more than 600 different species in Britain? They’re all about 1-3mm long, with six legs, a tiny head and a bloated, teardrop-shaped body, so you’d need to be an expert to tell most apart. However, they do come in a range of colours, including pink and brown, but the ones we’re most familiar with are the many species of ‘greenfly’ and ‘blackfly’. With names like that, you’d be forgiven for thinking they’re flies of some sort, but they’re actually members of the group known as ‘true bugs’. Their cousins include shield bugs and froghoppers (the ones that create cuckoo-spit), pond skaters and water boatmen. The word ‘bug’ gets bandied around very loosely these days to mean any creepy crawly, but ‘true bugs’ all have sucking mouthparts, like a sharpened straw. For aphids, this is a perfect tool to stab through soft plant stems to reach the delicious plant juices flowing inside.

Aphids rarely kill a plant, or at least not directly. Instead they weaken it, often causing it to grow deformed and reducing its crop of flowers or fruit. They also help transmit plant diseases, while the sugary honeydew they exude falls onto leaves and is colonised by sooty moulds. Viewed up close, aphids have a curious pair of tubes sticking up from their back. These ‘siphunculi’ secrete a waxy substance, which helps deter predators and also emits pheromones, which is how aphids communicate with their neighbours.

Aphid lifecycle

No aphid can survive our winter as an adult, so females lay batches of eggs in autumn, all with a hard casing to withstand cold weather. These hatch in spring, and every single aphid is female, capable of producing babies, which they do at an alarming rate. One female can give birth to 60 or so live young, and each of these can in turn become mothers in little over a week. Until now, all the aphids have been wingless. It’s only when the population becomes too much of a crowd that winged youngsters are born. These fly off to find another plant of the same type nearby; or some switch their attention to totally different plant species. It’s only at the tail end of the season that male aphids are born, which mate with the females who then lay their eggs and the cycle is complete.

Natural defenders

Given this endlessly exploding aphid population – in one season, a single aphid can have 300 billion descendants – it might seem like there’s no hope. Fortunately such profusion means ‘food, glorious food’ for the hungry aphid assassins (see below). However, these aphid predators will only frequent your garden if you make them welcome. For example, you won’t have adult ladybirds to produce all their aphid-chomping larvae if there are no undisturbed grassy clumps and plant stems in which they can spend the winter. Likewise, sparrows need nesting sites and food to see them through the winter; and the right type of nectar-rich flowers are vital for adult hoverf lies to feed on. So, your best chance of having nature keep your aphids in check is if you create a garden habitat that fulfils all the needs of their predators. A naturefriendly garden won’t totally rid you of aphids, but it helps create a healthy balance in which you don’t have to resort to chemicals. Working with nature definitely saves you time and money, and the revised aphid population that results will no longer be the stuff of nightmares.

“In one season, a single aphid can lead to 300 billion descendants”