Where did it come from? Were my plants being gobbed on by a passing bird perhaps a cuckoo? Well the legends around this foam would have you believe so, as it is commonly known as "cuckoo spit".
Cuckoo spit it is not however, unless global warming has brought about a generation of asthmatic cuckoo's who have severe phlegm problems. In fact you will also find this plant foam phenomenon called "snake spit" in those countries more blessed with snakes than cuckoos, and in these locations the name is also deceiving.
We call it cuckoo spit here in Ireland because it usually appears on plants around the time we begin to hear the cuckoo calling. Some people also claim the reason the name stuck is because our native cuckoo flower or Lady's Smock is often seen liberally decorated with the frothy substance.
The "spit" is in fact made by an insect, the young of the froghopper (Philaenus spumarius). The female froghopper lays her eggs in early summer, into slits and grooves in the stems of plants and wild un-mown grasses. The eggs hatch out in the following spring and the young nymphs emerge to clamber on to plant stems, where they then go on to produce nests of froth-like "cuckoo spit", within which they sit until they become fully mature frog hoppers.
Many plants play host to these young and the associated cuckoo spit, everything from pine trees to strawberry plants, however sap filled perennial flowers and grasses are favoured haunts. The yellowish nymphs pierce and suck on the sap of the plant allowing it to produce the foam not from its mouth like spittle but rather from the other end of its body, introducing air bubbles as it goes.
The white liquid acts as a protective coat to the frog hopper nymphs soft bodies, insulating them from drying heat and freezing cold, as well as hiding them from predators such as birds. Without doubt the cuckoo would like to have a go at them for framing him all this time.
So, are the young froghoppers a pest you should be worried about, and do they cause much damage? Well, you could say that as they pierce plants and suck sap; they cause damage and distortion of young shoots. The damage though is so minimal that I would advise you to leave them alone, they'll be gone in a few weeks at the most.
If you really can't bear them, or if the cuckoo spit is being produced on your home grown veg and herbs, then a strong jet of water from a garden hose should be sufficient to dislodge them. No nasty chemical sprays required.
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