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In this article, you’ll learn all about aphids, how they can actually be beneficial to your garden, and how to treat them organically if necessary. 


What are aphids? 

Aphids are small, sap-sucking insects in the Aphidoidea superfamily that can proliferate on plant stems and the underside of leaves. Aphids can be especially problematic for gardeners when they infest young seedlings or greenhouses, although they can also pose a threat to mature plants as well.      

What do aphids look like? 

Adult aphids are very small, about the size of a flea. They have a wide range of color from green to black to yellow, depending on the exact species, time of year, and host plant.

Most aphids are wingless. However, generations of winged aphids are born to find new host plants at certain points during the year and/or once the current host plant is no longer providing an adequate food source.

Aphids have one of the most bizarre reproductive patterns in the insect world. A single first generation female in the spring can potentially produce billions of descendants within a single season! 

How? Aphids primarily reproduce asexually during the warm months, giving birth to other genetically identical clonal females who are themselves born pregnant. It’s a bit or a horror show, like Matryoshka dolls of tiny, pregnant sap-sucking insects. They eventually reproduce sexually before fall to produce overwintering eggs.   

See the big black dot with the little black dots behind it on this onion leaf? That's an adult female aphid with tiny aphid nymphs behind her. Another 24 hours and there will be lots more small black dots on this spot.

See the big black dot with the little black dots behind it on this onion leaf? That’s an adult female aphid with tiny aphid nymphs behind her. Another 24 hours and there will be lots more small black dots on this spot.

 

So, if you notice a garden plant or seedling whose stem or leaves (on the undersides) are covered in tiny insects that seem to drastically multiply in number by the day, chances are that you’ve identified a population of aphids in your garden. 

Symptoms of aphids on your plants

The most common symptoms of aphids on your plants include:

  • sticky leaves (due to the “honeydew” the aphids excrete);
  • curled leaves;
  • weakened, limp, or dying plants despite adequate water and nutrition (especially with seedlings).

With aphid infestations in larger plants, you may also notice a dark colored mold (fungus) coating your plant leaves or on the ground under your plants. The fungus is growing on and eating the sugar and nutrient-rich aphid excretion, aka honeydew.     

The small yellow insects on this milkweed stem are aphids. The ladybug is eating aphids, and is one of many predatory insects who view aphids in the same way that a child views candy: delicious treats.

The small yellow insects on this milkweed stem are aphids. The ladybug is eating aphids, and is one of many predatory insects who view aphids in the same way that a child views candy: delicious treats.

Why are there ants all around the aphids on my plants? 

Another symptom of aphids is ants on your plants. Humans aren’t the only species on earth that have livestock. Aphids are to certain species of ants what cows are to humans.   

Red ants farming aphids on the underside of a curled leaf that protects them from the weather.

Red ants farming aphids on the underside of a curled leaf that protects them from the weather.

Various species of ants tend to a flock of aphids in much the same ways as cowboys. They’ll carry aphids to choice spots on the plant, protect them from predators, and even curl leaves over them to protect them from rain. In exchange, the ants get to enjoy an endless supply of sugary honeydew, similar to the way in which humans get milk from domesticated ruminants.      

Are aphids bad or good? 

As we’ve written about elsewhere, 95% of insects are beneficial or benign.

However, after reading the information above, you might conclude that aphids definitely fall in the “bad insect” category. In fact, you might consider them to be the most horrifying thing you’ve ever read about!  

Take a few deep breaths… Like pretty much everything that exists in nature, aphids also have a beneficial role in their ecosystem due to the fact that they’re a favorite treat for a huge range of predatory insects such as: 

  • ladybug adults and larvae,
  • parasitoid wasps,
  • lacewing larvae
  • syrphid fly (aka hoverflies) larvae, 
  • many species of non-webbing spiders,
  • the nymphs of a wide range of other predatory insects.  
Lacewing larva eating an aphid on the underside of a Mexican primrose leaf.

Lacewing larva eating an aphid on the underside of a Mexican primrose leaf.

In a healthy ecosystem, these predators typically hold aphid populations in check. We rarely encounter an aphid infestation in our garden that isn’t quickly wiped out by throngs of ladybug larvae and lacewings. The abundant food source (aphids) triggers the adult predators to lay eggs on the affected plants, and you soon get armies of predators to help you with pest management.      

Think of it this way: without plant-eating gazelles and wildebeests in the African Serengeti, there’d be nothing to attract or sustain lions, leopards, and other predators. The same predator-prey relationship pattern holds true all the way down to insects and even microscopic soil organisms. 

This ladybug is hunting wheat leaves for aphids. Unfortunately, the aphid just in front of it has already been parasitized by a parasitoid wasp so won't be a good food source. Too many predators in the buffet line!

This ladybug is hunting wheat leaves for aphids. Unfortunately, the aphid just in front of it has already been parasitized by a parasitoid wasp so won’t be a good food source. Too many predators in the buffet line!

Aphid-spread plant diseases

The winged generation(s) of aphids that goes in search of new food sources gives rise to what is perhaps aphids biggest threat to healthy plants: the spread of disease.

As these winged aphids go in search of the perfect new plant on which to wean a few billion offspring, they dig their needle-like mouthparts into plants along the way, like Goldilocks in search of the perfect bowl of porridge. In the process, if they come into contact with a pathogen, they can then infect downline plants as they go. 

Healthy plants grown in healthy, biologically active soil can fight off most plant diseases, but others won’t be so lucky.      

How do you prevent aphids in your garden? 

There is no way to prevent 100% of aphids from nibbling on the plants in your garden. Instead, you’ll want to focus on holistically managing them, and the best way to manage them is by attracting predatory insects to manage them for you. 

Three tips for attracting and maintaining high populations of predatory insects:

1. Utilize plant biodiversity. 

Plant a wide variety of plants, rather than growing monocultures. This practice prevents pests and diseases that love one type of plant from over-proliferating while encouraging a diversity of insect species.   

Lots of biodiversity in this image from part of our summer garden. Edible plants are mixed together with flowering plants. This type of system makes it very difficult for any one pest or pathogen to proliferate.

Lots of biodiversity in this image from part of our summer garden. Edible plants are mixed together with flowering plants. This type of system makes it very difficult for any one pest or pathogen to proliferate.

 

2. Plant multiple flowering species. 

Many of the small predatory insects that eat aphids also eat pollen and nectar. Even if they don’t, they’ll also hunt other smaller insects that are attracted to the flowers.

By planting a diversity of flowering plants — including plants like cilantro, garlic chives, yarrow, mache, and others that produce plentiful clusters of small flowers — you’ll attract a ton of beneficial predatory insects that will soon be enjoying an aphid buffet as well. 

A syrphid fly foraging cilantro flowers. Syrphid flies are excellent pollinators and their larva (which look almost slug-like) are voracious hunters of aphids.

A syrphid fly foraging cilantro flowers. Syrphid flies are excellent pollinators and their larva (which look almost slug-like) are voracious hunters of aphids.

Many organic farms also utilize perennial hedgerows and/or incorporate rows of wildflowers in to their fields to take advantage of this approach.   

3. Avoid pesticides/biocides, especially synthetics.  

“Pesticide” is a broad umbrella term used to describe substances designed to kill biological lifeforms. It includes herbicides, fungicides, insecticides, etc. Not surprisingly, a substance designed to kill a weedy plant may also kill or harm insects; a substance designed to kill an insect may also kill/harm a plant symbiont fungi, etc.

So, unless absolutely necessary, avoid using pesticides. If you do use them, opt for OMRI listed organic pesticides rather than synthetics. These types of pesticides tend to be plant-derived and have far less harmful and enduring impacts on non-target species.   

A ladybug larva (front) eating aphids on asparagus leaves while adult ladybugs (background) mate in preparation to make more ladybugs. If we had sprayed insecticides on this asparagus plant, we would have killed both predators and prey.

A ladybug larva (front) eating aphids on asparagus leaves while adult ladybugs (background) mate in preparation to make more ladybugs. If we had sprayed insecticides on this asparagus plant, we would have killed both predators and prey.

How do I get rid of aphids using organic methods?  

If you’re a gardener, you have the benefit of using one of the most effective techniques for getting rid of aphids on a small-scale: a garden hose sprayer. Simply blast the aphids off your plant(s) with a spray of water. 

If the infestation is too severe or you’re dealing with particularly annoying aphids, like wooly aphids, that can fly right back to the plant soon after being sprayed off, you may opt to use an OMRI-listed organic pesticide. In our experience, the one that works best is neem oil, which coats and suffocates the aphids. It also has an odor that insects don’t like, so can also be used as a preventative for other pest insects as well.  

When applying neem oil, just do your best to avoid spraying it:

  • directly on non-target insects, 
  • on flowers where pollinators are likely to visit,
  • during the morning or middle of the day when insects are likely to be most active. 

Also note that nothing you do will permanently get rid of aphids in your garden. Some will survive and proliferate again, and new ones will fly in to colonize your garden anew. Hence the importance of taking a holistic management approach and using nature to fight nature for you!  


Now you know more than you probably ever wanted to about aphids. Most importantly, you now know that aphids can and do serve a beneficial role in your garden ecosystem. If you do need to intervene to get rid of an aphid infestation, you know how to do so using methods and applications least likely to cause negative impacts to other species that make your ecosystem healthy and robust. 

Happy gardening!     

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