The Many Patterned Cuckoo-Spit Froghopper

Two Cuckoo-Spit Froghoppers, Philaenus spumarius, mating

Philaenus spumarius, the Cuckoo-Spit Froghopper, is one of the commonest bugs in Irish hedgerows and gardens, especially from June to August when the green-ish nymphs are quite conspicuous due to their habit of hiding in a mass of spit-like bubbles which shield them from predators (1). The adults remain well hidden though, thanks to their excellent camouflage. However the pattern of this camouflage is highly variable, so variable in fact that it has led to up to 50 different synonyms being used for P. spumarius (2).

Cuckoo-Spit Froghopper nymph

Polymorphism such as this is common in many other animal species and while the mechanisms controlling it has been much source of debate, it is accepted that control is genetically based on alleles of gene loci (3). Although P. spumarius is of holartic distribution, levels of polymorphism have been found to be highest in the Mediterranean, now thought to be the point of origin for the species (4). Here, polymorphism is selected for based on visual selection, specifically to avoid predators during the long obligatory period of aestivation that P. spumarius undergoes. Since vegetation on which the eggs are layed and development takes place soon vanishes in the harsh weather of the Mediterranean, individuals soon have to move to other hosts, various shrub and tree species. 

The Cuckoo-Spit Froghopper, Philaenus spumarius

However, in more northern parts of Europe, vegetation cover remains ever-green meaning movement is not needed and removing the visual selection for polymorphisms. Yet it does occurs in these areas too, most probably due to gene flow drift (4).

The Cuckoo-Spit Froghopper, Philaenus spumarius

References:

1. Sterry, 2004. Collins Complete Guide to Irish Wildlife p. 132
2. Nast, 1972. Palaearctic Auchenorrhyncha (Homoptera), an annotated Checklist
3. Halkka and Halkka, 1990. Evolutionary Biology 24 pp 149-191
4. Drosopoulos et al., 2010. Zoosystematics and Evolution 86 pp. 125-128