From May onwards globules of white foam start to appear on the stems of flowering plants and grasses. Centuries ago this acquired the popular name of cuckoo spit because it seemed to appear at the same time that the first cuckoos of spring were heard. Other popular names were snake’s spit, witches’ spit and frog spit.
The culprit is the tiny growing nymph of a bug called a Froghopper, which can be found inside the ball of foam. There are several froghopper species in Britain, all of which produce this protective foam, but the one most likely to be seen at St Nicks is the Common Froghopper, Philaenus spumarius. Adult froghoppers mate in summer and lay their eggs (up to 400 per female through the season) on a wide variety of plants and grasses. The adults live for about 3 months and die in the autumn after all their eggs are laid. Then when the plants die back with the approach of winter, the froghopper eggs are buried within and protected by the dying plant material. Here they overwinter, but the following spring the eggs hatch out into nymphs (the usual name for the larvae of true bugs) which crawl up growing plants and grasses and fasten their mouthparts into the soft stems. This is when the spitting begins!
The nymph bites into the stem and grows by feeding on the plant’s xylem sap. After absorbing the nutrients in the sap it excretes the remaining water in bubbles. These bubbles increase to cover and encase the nymph in foam which has a threefold function: it hides the vulnerable nymph from would-be predators; it prevents the nymph from drying out; and it acts as a thermal blanket insulating the nymph against changes in outside temperature. There is normally only one nymph in a ball of foam.
True bugs have no pupal stage. As the nymph grows it sheds its skin several times until it emerges as a winged adult and crawls out of its protective blanket.
Adult froghoppers have a large number of colour variations, and identifying the exact species is not always easy. The adults get their name Froghopper (it is also known as Spittlebug) from their appearance and jumping ability. When seen close-up they have wide heads and mouthparts and resemble a tiny frog. This wide mouth is also seen in the nymphs because both need strong mouthparts to pump out the plant sap. The adults don’t make foam when they feed, but simply excrete the excess water.
The adult froghopper’s jumping ability is phenomenal. Using its rear legs it can jump (often with an audible click) up to 70cm, the equivalent of a human jumping over a tower block. Human beings can withstand around 5g of accelerational pressure (e.g. during a manned rocket launch) before passing out. A grasshopper can withstand about 10 times. A flea – a legendary big jumper – can withstand 135g, but the froghopper beats all, at 400g.
The froghopper’s only enemies appear to be parasitic flies or wasps which have evolved to recognise the spit ball as the ‘home’ of the nymph, and lay their eggs in the foam. When these eggs hatch, the larvae burrow into the body of the froghopper nymph. The fly larvae consume the nymph before pupating and finally emerging as adults.
Gardeners sometimes consider cuckoo spit to be unsightly on garden plants, and possibly damaging, but in spite of its feeding habits there is little injury done to any plant by froghoppers and we should happily tolerate these intriguing and athletic little bugs both in our gardens and at St Nicholas Fields.
All photos were taken at St Nicks