Why you should leave aphids alone

I often hear from gardeners who are worried when they discover a few aphids on their favorite rose. While aphids can be troublesome garden pests, especially when their population numbers more than about 12 aphids per square inch, more often than not, aphids aren’t anything to worry about. In fact, it’s actually good to have a few aphids around. Let me explain.

Aphids are small, soft-bodied, pear-shaped insects that feed through a needle-like mouthpart. After they insert their mouthpart into a plant’s tissue, they then use it like a straw to suck out plant juices. Severe infestations can cause distorted plant growth, no doubt, but if your garden has a healthy number of beneficial insects, aphid numbers will seldom grow large enough to cause plant damage.

Aphids aid benefical bugs

You see, aphids are food for thousands of different species of predatory insects. Most gardeners know that certain ladybug species eat aphids, but many other beneficial insects feed on them as well, including lacewing larvae, ground beetles, soldier beetles, robber flies, syrphid fly larvae, tiger beetles, rove beetles, parasitic wasps and many, many more.

By having a few aphids around, you’ll help boost your population of these very beneficial insects, that also happen to eat many other common garden pests as well. While not all beneficial insects eat aphids, these pests can help sustain a broad diversity of them, leading to a more balanced garden that’s less prone to pest outbreaks of all sorts.

In order to have lots of “good” bugs around, you also have to have some pests around, too. Otherwise the beneficials will leave for greener pastures, so to speak. Aphids are excellent for this purpose since, even with a severe infestation, they will not kill their host plant.

In my own garden, I always leave the aphids alone. Since I’ve been nurturing beneficial insects for the past 10 years or so, I have plenty of them around and the aphid population never gets out of control anymore. It’s fun to see which beneficial insects show up to help me manage the aphids.

On my milkweed plants, which are always attacked by oleander aphids each summer, I often spy ladybug larvae, lacewing larvae and syrphid fly larvae enjoying the aphids for lunch. Within about two weeks, the aphids are totally gone. On my nasturtium leaves, I find plenty of aphid “mummies.” These brown, swollen aphids have been parasitized by a particular type of parasitic wasp, known as aphidius wasps, that use aphids to house and feed their developing larvae. And on my tomato plants, when aphids arrive, they’re soon discovered by the spiders who glean them off the plants at night (yes, I’m the kind of garden nerd who goes out to her garden at night to see what all my nocturnal good bugs are up to!).

While I’m not suggesting you should let aphids take over your garden, I am recommending that you leave many of them be, to help build your good bug population over time. After a few years of this practice, combined with a general elimination of pesticides that could also negatively impact beneficial insects, you’ll find that you seldom face any severe pest infestations at all.

Leaving aphids be is a great first step in regaining a balance of good bugs and bad in the garden.