Aphid Killers

Aphids spend their entire lives sucking sap from garden plants and spreading viral diseases, but those lives are fraught with danger.

Ladybug larvae eating an aphid (Judy Gallagher) CC BY 2.0

Aphids are soft-bodied insects with piercing mouthparts. They insert their sharpened straws into plant tissue, where they slurp up copious amounts of sugary sap. They eat so much and so quickly, that much of what they eat simply goes in one end and out the other. This “honeydew” can be contaminated with pathogens and it attracts the attention of protective ants, but aphids have many enemies. We’re not just talking about gardeners here, either. In most cases, aphid killers are either predators or parasites, though there are exceptions.

Parasites

Parasitoids are insects that lay their eggs in, on, or near host insects. Those hosts end up being the first meals for parasitic larvae. There are many parasitic wasps that bring death to aphids. They do this by laying an egg in every aphid they can. When the eggs hatch, they eat their aphid hosts from the inside out. Gruesome, right?

Aphidius ervi (Nikk Valentine) CC BY 2.0

Braconid wasp (Richard Bartz) CC BY-SA 2.5

Eventually, the aphids die and the now-adult wasps fly away. All that’s left behind are dozens of tan or golden aphid husks known as mummies. If you use a hand lens, you may even be able to see wasp exit holes.

Aphid mummies (James Marchment) Public Domain

The most commonly seen parasitic wasps and their favorite aphids include:

• Aphidius colemani–prefer smaller species, such as melon aphids (Aphis gossypii) and green peach aphids (Myzus persicae)
• Aphidius ervi–prefer larger aphid species, including potato aphids (Macrosiphum euphorbiae) and foxglove aphids (Aulacorthum solani)
• Braconid wasps–these tiny predators parasitize many garden pests

Big-eyed bug (Patrick Kavanagh) CC BY 2.0

Predators

Predators actively hunt and eat aphids. Aphid predators include:

• Aphid midges
• Beetles--blister beetles, ground beetles, ladybugs, rove beetles, and soldier beetles
• Big-eyed bugs
• Birds—American goldfinches, house finches, hummingbirds, sparrows, titmice, warblers, and some woodpeckers
• Damsel bugs
• Earwigs
• Green and brown lacewings—their larvae are affectionately known as “ant lions”
• Hoverflies

Remember those exceptions I mentioned? One of them is the ichneumon wasp. Adult ichneumon wasps kill their prey outright and then lay eggs in the corpse. It’s a brutal world out there, make no mistake.

Ichneumon wasp (Bruce Marlin) CC BY-SA 2.5

Many varieties of parasitic wasps and other aphid killers are available for purchase, but you can often attract these garden helpers to your landscape with plants that provide abundant nectar and pollen. Queen Anne’s lace, coreopsis, coneflowers, cosmos, coyote brush, dandelions, dill, goldenrod, sweet alyssum, and sunflowers look lovely and they create a natural welcome mat to insects that see aphids as the perfect meal. Hedgerows also provide beneficial insects with good hiding places.