The Selective Squish: Aphids

I am lucky to be in a gardening group with a friendly email list. We share plants, news, tips, questions. Today, someone asked what to do about April aphids on a late-blooming aster, and added, “There are a gazillion of them on the plant (I counted).” 

This is someone who had done due diligence by looking for answers, but had found too many: No, don’t kill; Yes, do kill, but only with this, not that. What should they do?

What I should have done was congratulate them on having late-blooming asters—so important for late-season nectar / pollen / leaves / seeds! —and on trying to find a “best practices” solution to avoid harming the foodweb.
Good job, gardener!
But what I did was jump right in with zero manners and lots of info:

[Too-Long-Didn’t-Read version: pesticides will kill aphid predators along with the aphids.]

This time of year, most aphids are wingless, so they can’t fly away from us if we decide The Big Squish is required. The Big Squish = running a thumb and forefinger along a stem (or using a moist paper towel if squeamish). 

Actually, it should be called the Selective Big Squish. Please keep reading to see what not to squish.

Aphids suck. Our plants. And right now, mid-April, we’re in an aphid boom, because aphids emerge *before* aphid predators appear in numbers large enough to make a dent. 

But, the ratio of aphids vs predators is changing in our favor. For example, my fleabanes are covered in aphids at the moment, but they are also covered in two big clues that tell me aphid predators are showing up for work.

1) I see aphid mummies:

These little beige balls are actually aphids “mummified” by a parasitoid wasp. The wasp lays an egg on the *inside* of the aphid. When the larva hatches, guess what it eats? The *inside* of an aphid. The larva grows until time to kill the aphid, and then it pupates tucked safely inside Mummy Dearest.
Days later, the new adult wasp flies away to mummify more aphids. If you see a tiny exit hole in the mummy, you know the drama is complete.

From a gardener’s point of view, an aphid mummy is a double bonus: an aphid that won’t suck our plants (because it is either dying or dead), but will generate more predators who kill more aphids.

2) I see hungry larvae of lacewings and hoverflies and ladybugs:

I see all three on my fleabane as they hunt and eat aphids. Female adults of these and other predators purposely lay eggs near aphids, so that the babies can hatch at an aphid buffet.

When I find one of these hunters in the grass (or on a dirty ballcap, as pictured above), I’ll move it to the plant with the most aphids, and then watch the hunt. It’s fascinating. 

Here’s the gist:
Don’t use pesticides on aphids.
Any pesticide—even homemade insecticidal soap, even diatomaceous earth—will kill the aphid predators along with the aphids.


When an aphid population boom is big enough, aphids start producing more winged adults who can fly to a new plant and start a new community with fresh food.

By the way, most aphids right now are female—maybe all of them?—and the new babies have come not from eggs but from live birth, and with no help from a male aphid. Asexual reproduction. Parthenogenesis! 
Eggs are coming, though. The genetics are too confusing, but aphids can also reproduce sexually, with live birth and with eggs. What gardeners need to know is that the late-season eggs are how aphids overwinter. That way, aphids can hatch in early spring and start sucking our plants before the predators get going.


My aphid solution at home is to move predators around and then Wait-and-See. Every time, when I check the next day, I find fewer aphids.
Then again, I have an abnormally high tolerance for insects. 
And then again, it is my dream to watch an aphid give birth. Parthenogenesis in action!

But I also have empathy for people who are driven nuts by a particular insect. I used to lose my mind over Eastern Carpenter bees (link to that happy ending is here).

So, if a gardener’s mental health is threatened by a gazillion aphids, I might recommend a Selective Big Squish.

Selective Big Squish = aim for the live aphids and miss ALL the predators and all the mummies.

-Why not squirt the plant with a hose? Because the squirt might kill the predators.
-What species of aphids do we have in Nashville? Plenty. But here’s a fun thing: if you see aphids the color of orange sherbet, you are probably looking at a plant in the milkweed family. This is a great way to ID those weedy but wonderful milkweed vines that host Monarchs.
-Who else eats aphids? Birds can, if the right bird and the right aphid. Like, even those exotic white, wooly aphids who suck Hackberry leaves get eaten by our resident insect-eating birds and Fall warblers.
But as for other bugs who eat aphids, here’s a page with photos of many aphid predators: link. Do not squish.

More aphid and aphid predator posts at SidewalkNature:
Aphid Alarms post
Aphid Lion post
Lacewing egg post
Instagram video of aphids and ants action on a milkweed leaf (and mummies, etc.)
Instagram video of lacewing trash bug looking for aphids


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Joanna Brichetto is a naturalist and writer in Nashville, the Hackberry-tree capital of the world.
She writes about everyday marvels amid everyday habitat loss at and on Instagram (@Jo_Brichetto); and her essays have appeared in Creative NonfictionBrevity, Ecotone, Fourth Genre, Hippocampus, The Hopper, Flyway, The Common, The Fourth River, and other journals. An almanac of urban nature encounters is forthcoming.