Cuckoo Spit

Every May white blobs of foam start to appear on shrubs such as lavender and rosemary; this year because it was so cold in late winter/most of spring they are later.  A few days ago I started to notice that they had begun to appear and here is one on my rosemary:

Looking a bit out of focus as I am rather in between cameras at the moment, looking for one that takes a good closeup.  I expect this looks familiar if you live in the UK but what is it and what does it have to do with cuckoos?

This is the larval form of a wee insect called the froghopper.  It causes no harm to plants whatsoever and please don't try and get rid of it as it will soon vanish when the nymph is old enough to leave the foam.  The adults are sap suckers and will appear in late summer; again they don't do any harm.  They lay their eggs at this time of the year which will lie dormant over winter and emerge in the spring in their protective blobs.  These keep the nymph moist and taste nasty to predators, as well as keeping them warm.  There is more than one type of froghopper that does this and other common names for the foam include snake spit and frog spit; the cuckoo part presumably refers to the time of year it appears as it has nothing to do with cuckoos!