What's That Bug? does not endorse extermination

Tiny bugs all our fence!
November 13, 2009
We live in Philadelphia and over the past few months part of our back yard fence has been colonized by these small (3mm) insects. There are hundreds of them. The fence runs underneath a weeping willow tree, and they appear to also be on the willow. The bugs move fairly quickly. I’ve tried sweeping/blowing them away, and they return hours later. When you squish them it leaves a purple residue. Our landscaper thinks that based on the speed of the insect, that they’re probably a “beneficial”. Any thoughts?
Sam Blackman
Philadelphia, PA (Northwest corner of the city)

Unknown Hemipterans

Black Willow Aphid

Hi Sam,
WE are not having much luck with a definitive identification.  At first we thought these were immature True Bugs, but we cannot find any images that match.  Then we thought perhaps they might be Aphids, which are in the same insect order as the True Bugs. There is a
Giant Willow Aphid, but it doesn’t match your specimens.  We think we need to seek assistance from Eric Eaton and our readership on this identification.

Unknown Hemipterans

Black Willow Aphid

We were not content with giving up, and we located a reference on the UMN Yard and Garden News website for a Black Willow Aphid, with no scientific name.  It is described by Jeffrey Hahn as:  “Black aphids with orangish or brownish legs and cornicles (the tail pipes of an aphid) on willow are black willow aphids. They are large for an aphid, reaching up to 3/16th inch in length. They can be quite abundant in August and September. These aphids are common on willows and may also be found occasionally on poplars and silver maples.
Black willow aphids secrete honeydew, a sticky sugary substance which will coat any object underneath an infestation. Yellowjackets may be attracted to infested trees because of the honeydew. In addition to being a problem in trees, these aphids sometimes have an annoying habit of dropping to the ground and collecting around buildings and nearby objects. If their bodies are crushed, they can stain siding and other objects a blue-purple color.
Despite their abundance, they do little if any lasting harm to established, vigorously growing trees. Their presence is just a nuisance. Tolerate these aphids as much as possible. If you wish to reduce their numbers, try washing them off as many branches as you can reach with a hard spray of water. A less toxic insecticide option would be treat them with insecticidal soap. If nothing is done, their numbers will diminish on their own by the end of the month.
”  That led to an image on Flickr with the scientific name Pterocomma salicis.  That brought us back to BugGuide.  The images online of the Black Willow Aphid are spotted, but other than that, they resemble your insects.  We still hope to get assistance with this ID.

Unknown Hemipterans

Black Willow Aphid

I think it might be a willow aphid of sorts, just not the one you were thinking of.  I think these might be Pterocomma salicis instead, but I am by no means positive.  At this time of year aphids are changing to alternate host plants for the winter, too, so that can really throw things off.  Aphids of the same species can, in at least some cases, look completely different depending on whether they are on the primary host or the alternate host.

What's That Bug? does not endorse extermination
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11 Responses to Probably Black Willow Aphid

  1. Colleen Smith says:

    We have a lot…. Millions… Of these bugs. It is awful!! They are all over the kids toys, swing set and killing my willow tree. I really need help getting rid of them. I won’t let the kids outside now. I spray them with water and they come back. What should I do???

  2. Carol Braun says:

    I am experiencing the same problem. They are covering my tree, and other objexts siting in my yard, like our garbage cans. I am spraying them with a mixture of Dawn dish soap and water. They are still in our tree, but I spray around the house etc and have noticed they have slowed down. After spraying, the bugs are kinda dried out, and don’t leave a purple stain like when you crush them.

  3. Mohsin says:

    In green house i planted willow seedlings from last week i oberving the coleoptra in willow ports. could you suugest me any kind of solution to get rid off from these tiny insects.

  4. […] an infestation. Yellowjackets may be attracted to infested trees because of the honeydew. (https://www.whatsthatbug.com/2009/11/14/unknown-willow-aphid/). The yellow jackets surprised us many times and then they became an integral part of the […]

  5. paule says:

    These have just shown up. We’ve lived here for 30 years with large willows and never have seen them before. Thousands upon thousands. Insecticide kills them on contact but seem to be impervious to the residue of the poison and does not affect them. Can’t spray the tree cuz it’s over 60ft tall.

  6. Kimberly Weggeland says:

    I have been searching for days and I finally have somewhat of an answer. I am happy that I found this because I have the same issue as stated above and it has really been “bugging” me. Thanks for writing this!

  7. Melissa Engelhard says:

    Are Black Willow Aphid harmful to chickens? They are all over the outside of my chicken coop.

  8. Rachel says:

    Here in Minnesota we had these insects ALL over our backyard. I’ve never seen them before until this year. I did as much research online as I could and came up with nothing till this post. I will say that we did spray with an insecticide. However we ended up spraying the hanging branches of the neighbors weeping willow tree. That worked like a charm and they haven’t come back.

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