03/06/2006

Trees and plants have suddenly become covered in frothy liquid - that's nothing to do with Cuckoo's!

Although it appears at about the same time as cuckoos are heard, this froth has no connection with any bird.

it's actually secreted by the immature stages of sap-sucking insects known as froghoppers, presumably as a means of protecting themselves against predators. The adult insects live openly on the plant and do not produce any cuckoo spit. Adult froghoppers are between 4mm and 7mm long. They are called froghoppers because from above they appear frog-like, and they are able to hop significant distances when disturbed. Adult females lay up to 100 eggs in late summer into an incision made into the tissues of the host plant. The eggs hatch the following spring - so this years cuckoo spit is produced by the young insects hatched from eggs laid last summer.

The froth serves a number of purposes. It hides the small undeveloped insect (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 bug would quickly dry up. The nymph feeds head downwards with its syringe-like mouthparts embedded in the tissue of the plant. The froth is created by the insect excreting excess undigested plant sap, mixed with a secretion from the abdominal glands. Air bubbles are introduced through a special valve on the abdomen which acts like a bellows, and contact with the air causes the liquid to ferment, forming the froth.

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