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Every year in May/June I'm observing on different plants, such as strawberries, lavender (pictured below) and different weeds, a foamy liquid containing a green insect or a larvae.

At first I thought that this is the work of slugs, but now, that I was able to find a "bigger" exemplar and I saw it was moving.

I'm really sorry for the quality, I only had my cellphone at hand at that time:

What is it and is it a pest or canI just leave them alone? On affected plants I never noticed any damage or negative side-effect, but that doesn't mean there aren't.

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  • Just for interest's sake, in the UK, we call this 'cuckoo spit' - no idea why, just the common name. Same cause though, froghoppers.
    – Bamboo
    May 27, 2015 at 16:44
  • @Bamboo Isn't the May also the month of the cuckoo in the UK? Apparently, the Froghopper's larvae is "hatching" at the same time. Maybe this is correlated.
    – Patrick B.
    May 27, 2015 at 20:14
  • You may be right - since it seems like centuries since I heard a cuckoo, I can't recall what month that might have been!
    – Bamboo
    May 28, 2015 at 11:51
  • @Bamboo let me tell you, it is right now, since ~3 weeks they can't stop cuckooing.
    – Patrick B.
    May 28, 2015 at 20:44
  • Oh lucky you - I had to check where you are to find out why you've got cuckoos. Don't get 'em in London
    – Bamboo
    May 29, 2015 at 10:10

3 Answers 3

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These are Froghopper larvaes. Also, known as Splittlebugs.

Wikipedia also shows the adult which I, of course, have seen in my garden.

Best thing about it: They are harmless in small quantities. No need to treat.

Update: Look who turned up this evening: a parent (Cercopis vulnerata)

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In this article "F is for Froghopper" the following is written about the foam:

"The real secret behind ‘cuckoo spit’ is much more interesting than coughing Cuculidae anyway. It’s a froth produced by the nymphs of smallish Hempiteran insects known as froghoppers, which they manufacture by blowing bubbles into the plant saps on which they also feed. This custom-made nursery serves to protect the delicate nymphs from drying out, as well as hiding them from predators."

Here is a quote from the wiki:

"The froth serves a number of purposes. It hides the nymph from the view of predators and parasites, it insulates against heat and cold, thus providing thermal control and also moisture control; without the froth the insect would quickly dry up. The nymphs pierce plants and suck sap causing very little damage, much of the filtered fluids go into the production of the froth, which has an acrid taste, deterring predators. A few species are serious agricultural pests."

I myself have been wondering about this since I was a kid. I forgot all about it until I saw this post. Great finally getting knowledge about this fascinating phenomena.

Thank you.

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That's a sap sucking bug.

I don't know the scientific name, but I refer to them as "foamy aphids" for obvious reasons. They are sucking sap out of your plants, so I normally class them as a problem/pest, albeit not a severe one in most cases. They seem particularly fond of my tarragon.

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  • Over the years I checked several of these foams and never I saw more than one aphid inside, most of the time very small - the one pictured was "big" 2-3 mm. Is that normal?
    – Patrick B.
    May 27, 2015 at 12:59
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    These are not aphids. The other answer correctly identifies them as Froghopper larvae. Froghopper larvae are not as damaging to plants as aphids, so identifying them as such would lead to unnecessary treatment.
    – Mr. Mascaro
    May 27, 2015 at 16:15
  • @Mr.Mascaro I answered my own question following this answer. I just did the follow-up search using "foamy aphids" and found what I based my answer on.
    – Patrick B.
    May 27, 2015 at 16:24
  • @PatrickB., I wasn't refuting your answer. Aphids are a different family of insects.
    – Mr. Mascaro
    May 27, 2015 at 16:25
  • @Mr.Mascaro Yes. I just wanted to say that this answer, even though not correct in technical terms, helped me to find the right answer
    – Patrick B.
    May 27, 2015 at 16:27

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