Cuckoo Spit and Xylella – The Story So Far

Cuckoo Spit on the lavender in the front garden

Dear Readers, I am a member of several garden wildlife and insect groups online, and during this past week I have seen a rise in questions along the lines of ‘ I have cuckoo spit on my lavender, should I hose it all off? Is there any way to get rid of it? Are we on the verge of Armageddon?’ As someone who is entranced with the miracle of these annual foamy masses and the insects that make them, I figured that someone had gotten hold of the wrong end of the stick, and so they have. Reports that have superficially demonised the froghopper have appeared on the BBC and in most major and local newspapers, and I am frankly bewildered by the lack of knowledge shown. Science is often complicated, and it’s sometimes easy to read a headline and panic. So here is what is happening, as I understand it, and here is what we should be doing.

  1. What is cuckoo spit?

Cuckoo spit is produced by the nymph of the froghopper, a ‘true bug’ which feeds on the sap of plants such as lavender and rosemary. The froth is a protection for the toothsome youngster: it is produced from the insect’s excreta, and is turned into froth by the creature passing air through its anus. As I put it in my original piece on froghoppers here,

‘The foam is the only protection that Froghoppers have, and schoolchildren are always delighted by how it’s made. The bug sucks up the sap from its chosen plant, excretes what’s left, and blows air through it – so, it lives in a house built from faeces, and created by flatulence. What youngster could resist such a story? I’m surprised that they’re not all queueing up to be biologists as we speak.’

2. Do froghoppers do any harm?

The RHS website says that froghoppers rarely cause any real damage to plants, and can be left unmolested. I concur. My lavender has been a-froth with froghoppers for years, and is still splendid.

Froghopper nymph denuded

3. So why all the sudden fuss?

A bacterial disease known as Xylella fastidiosa, first discovered in the US in the 1890’s, is on the move. It turned up in Brazil at the end of the 20th Century, was in Europe by 2013 and has been advancing at a surprising pace. It was previously thought to be confined to warm areas such as the olive plantations of Greece, but in the past few years it has been found in France and Germany. Xylella works by blocking the uptake of water to the plant, and can be devastating – it has been identified in over 560 species of plant worldwide. In the UK, trees such as the oak and plane are thought to be most at risk. The RHS and DEFRA have been putting plans in place to arrest the spread of the disease if (or more likely when) it arrives. It is not, as far as we know, here yet.

The disease is probably going to arrive in the UK via a plant imported by a garden centre or tree nursery.  – the most recent outbreak of the disease was in Oleander, a popular garden plant in this country. However, once here it could be transmitted via sapsucking insects such as the froghopper. Although froghoppers are homebodies and don’t usually move more than about 100 metres during their lifetimes, they can be carried much further by the wind.

Photo One by By Charles J Sharp - Own work, from Sharp Photography, CC BY-SA 4.0,

An adult froghopper (Philaenus spumarius) waiting to ping away. It is a very froggy-looking creature! (Photo One)

4. Why all the requests to report cuckoo spit?

This is pre-emptive. It’s hoped that by building up a picture of where froghoppers are at the moment, it will be easier to understand exactly when the insects are active and the extent of their range.  I will be reporting my froghoppers to the iRecord site below, which can be used to report other critters too, and is very useful for getting a picture of what’s around in your local area. You will need to set up an account, and then you are looking for a ‘project-specific record’ – the project is ‘xylem-feeding insects’, and the common cuckoo spit froghopper’s Latin name is Philaenus spumarius. There is a useful pictorial guide here, just in case you have one of the other two common British species.

5. What is being done to fight the disease?

Certain EU regulations are already in place to control the spread of the disease: this is from the Henry Doubleday website.

  • All plant importers have to show evidence that their plants are sourced from areas that are free from Xylella.
  • Proposed imports of host species such as plane, elm and oak plants must be pre-notified to the UK plant health authorities to enable inspection This will allow a sequence of spot checks at the UK borders.
  • Other regulations are in place that restrict movements of specified host plants from the infected region of Apulia in southern Italy, and from countries outside the EU, to reduce the risk of entry.

However, if it did become established in the UK, control would focus on the targeted removal of host plants and management of the vector insects’ habitats. An outbreak (as opposed to an isolated incidence) would mean eradication of all possible hosts within 100m of the outbreak and very tight restrictions on commercial plant producers or garden centres within 10km of the outbreak for 10 years.

In other words, this is an extremely strong incentive to garden centres to ensure that their plants are properly sourced.

Photo Two by By I, Pompilid, CC BY-SA 3.0,

Oleander infected by Xylella (Photo Two)

6. What plants does DEFRA consider are most at risk?

In addition to the oak and plane, there are a whole range of other plants who would be endangered by Xylella.

  • Acer rubrum L.
  • Catharanthus roseus (L.) G.Don
  • Citrus sinensis (Linnaeus) Osbeck
  • Coffea L.
  • Gramineae Adans., Nom. Cons.
  • Medicago sativa L.
  • Morus rubra L.
  • Nerium oleander L.
  • Platanus occidentalis L.
  • Prunus L.
  • Prunus persica Batsch
  • Quercus rubra L.
  • Ulmus americana L.
  • Vaccinium L.
  • Vinca minor L.
  • Vitis L.
  • Woody plants
  • Liliaceae (family)
  • Citrus

7. What are the symptoms of Xylella?

Unfortunately, Xylella can look rather like many other diseases. The Forestry Commission says that:

‘The visible symptoms on plane, maple (Acer), oak and elm trees include leaf scorch, sometimes also with dieback of twigs and branches. The characteristic leaf symptoms which are visible in summer include browning at the leaf margins (but not along the main veins), and there is often a yellow edge to the browned areas.’

I suspect that concrete identification can only be achieved by scientists with microscopes. The bacteria produces many different species-specific syndromes, varying from oleander leaf scorch to citrus variegated cholorosis to olive quick decline syndrome. You will have noticed that many of the plants attacked are important food crops, often intensively grown and lacking in genetic diversity. There is much to be said for proper husbandry and stocking, and for the preservation of different varieties of plants, for just this situation.

The bacteria works by blocking the xylem, the main water-transport system of the plant. If only a few vessels are affected, the plant might be asymptomatic but still a carrier of the bacteria. If it is planted elsewhere and subsequently fed upon by a froghopper, the bacterium can be spread to another plant. The infected plant can also transmit the disease if it is grafted to a healthy plant.

Photo Three by Alexander Purcell, University of California, - [CC BY 3.0 (]

Pierce’s disease, caused by Xylella, on citrus (Photo Three)

8. Do we have to worry now? Should I be hosing off my froghoppers and burning my lavender?

No. As mentioned above, the reporting of cuckoo spit is pre-emptive. Our froghoppers are currently completely innocent, and will hopefully remain uninfected with Xylella. I think it is a hopeful sign that DEFRA and other bodies are getting on the case now, in unison with the EU, in order to head this threat off at the pass before it gets to the UK. We have already lost our elms, are likely to lose most of our ash trees, and our horse chestnuts are under siege every year. Let’s hope that this will be one disease that doesn’t get a grip.

Photo Credits

Photo One by By Charles J Sharp – Own work, from Sharp Photography, CC BY-SA 4.0,

Photo Two by By I, Pompilid, CC BY-SA 3.0,

Photo Three by Alexander Purcell, University of California, – [CC BY 3.0 (]

16 thoughts on “Cuckoo Spit and Xylella – The Story So Far

  1. Anne

    A wonderfully informative article. We get ‘cuckoo spit’ here too. I am sometimes first alerted to its presence in trees when I feel drops on my neck – look up and there it is. Your introduction takes me back to my childhood, when we often found ‘cuckoo spit’ on grasses and leaves. It was fun to wiggle through it with a grass stem to see how meany creatures we could find within that foamy mass.

  2. Sarah

    Thank you! I was glad to read this as I too have been frustrated by anti-froghopper panic. I will share this article. I find it amazing and depressing that we are still importing plants such as plane, oak and elm from other countries when we can so easily grow them here. It is dangerous madness.

  3. tonytomeo

    This is only the second time I have heard it referred to as ‘cuckoo spit’. The first was just a few days ago. As amusing as the explanation is, I would likely find alternative explanation. It all depends who I am explaining it to. I get embarrassed just explaining what honeydew is. Ick!
    Anyway, ours are a different species, or if I remember correctly, two species. One also gets rosemary and lavender, although xylella is not here yet. The other species gets the periwinkle, which most of us would prefer gone anyway. Unfortunately, they do not harm it.

  4. Alyson

    It was my late neighbour who first pointed out “cuckoo spit” in our gardens but I had never really investigated what caused it. Thanks for the info (and great pictures) as ever.

    1. Bug Woman

      Hi Bernard when you get into the survey you have the option of entering your postcode – you need to register first and then you can do it. Thanks for reporting, I’m sure it will all help to build up a picture of what our current froghoppers are up to….

  5. Hazel Mullan

    Hi, I have been trying to put information into this survey but so far unsuccessfully. The sticking point seems to be the name of the host plant ( Honeysuckle in this case, or Lonicera Serotina). Anyone else having problems? This is the only part of the survey that gets highlighted as an issue, and I’m told that my data wont upload.

    1. Bug Woman

      The site is sometimes a bit of a pain 🙁 – have you tried emailing the admins there? I reckon there must be some contact details somewhere….

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