Meet the aphid assassins

These hungry young predators will chomp through clusters of greenfly and blackfly… Adrian Thomas sings the praises of our tiniest gardening allies

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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, there’s no doubt you give a cry of dismay and maybe feel the urge to reach for the chemical sprays. But, help is at hand – there is an army of aphid-munchers who are eager to help you out.
Before we meet your knights in shining armour, it’s always 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? You’d need to be an expert to tell most apart, as they’re all about 1-3mm long, with six legs, a tiny head, and a bloated, teardrop-shaped body. 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. However, they will weaken it, often causing it to grow in a deformed way and reducing its crop of flowers or fruit. They also help transmit plant diseases, while the sugary honeydew they exude falls onto the leaves allowing sooty mould to grow.
If you get up really close to an aphid, you will notice that they have a curious pair of tubes sticking up from their back. These ‘siphunculi’ secrete a waxy-like substance, which helps deter predators, but they also emit pheromones which is the aphid's way of communicating with its neighbours.
No aphid can survive our winter as an adult, so the females lay batches of eggs in autumn, all with a hard casing capable of withstanding the cold weather. These hatch in spring, and every single aphid at this stage is female. However, in one of nature’s miracles, this doesn’t matter – the aphids can produce babies anyway, and do so 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 of 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; indeed, in the case of some aphids, which start the spring on tree leaves, they now switch their attention to totally different plant species in your veg patch or flower border.
It’s only at the tail end of the season that male aphids are born, and these mate with the females who then lay their eggs and the cycle is complete.
Given this endlessly exploding aphid population, it might seem like there’s no hope. It has been calculated that just one aphid could lead to a population of 300 billion by the end of the season. Fortunately such profusion means ‘food, glorious food’ for the hungry aphid assassins (see panel). 
All this sounds like a wonderful natural solution to the aphid problem but it’s important to remember that these aphid predators will only frequent your garden if you make them welcome. For example, there will be no 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, there will be no sparrows if they have no nesting sites or if there isn’t enough food to see them through the winter; and there will be no hoverflies if there are few nectar-rich flowers of the right type for the adults to feed on.
So, your best chance of having nature keep your aphids in check is if you create a habitat that fulfils all the needs of their attackers. The nature-friendly garden won’t totally rid you of aphids, but it will help create a healthy balance in which you don’t have to resort to chemicals. Working with nature will definitely save you time and money, and the revised aphid population that results will no longer be the stuff of nightmares.

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