If you visit the new biodiversity gallery in the National Museum in Cardiff, you will stumble across a fascinating study of spittlebugs (the same insects that produce ‘cuckoo spit’) in the Cynon Valley. Mike Wilson of the National Museum explains more about the dark coloured spittlebugs of the Cynon…

Industrial melanism is “adaptive melanism (dark coloured morphs) caused by anthropogenic alteration of the natural environment in terms of industrial pollution”. Most will know of the industrial melanism shown in some adult butterflies and moths - the peppered moth is perhaps the best-known example. However, there are a good number of others insects in which this has been shown and among them the common spittlebug Philaenus spumarius. This is an abundant insect in many habitats in the UK and continental Europe. It is a xylem sap-feeding insect feeding from a wide range of herbaceous plants. There is one generation each year, overwintering as eggs and the nymphal stages are present within spittle masses on the host plant. The adult insect occurs in a wide range of colour forms, which depends on the amount of darker pigmentation. The proportion of the different forms in different locations has been widely investigated both in the UK (e.g. Lees et al. 1983 Biological Journal of the Linnean Society 19: 99-114) and especially in Scandinavian localities.

There are a number of dark forms, which are found to occur in relatively low percentages in most of the UK. Around 30 years ago dark forms were found to predominate in the vicinity of the ‘Phurnacite’ factory in the Cynon valley in South Wales. The results of a sampling programme were published by Lees & Dent (1983 Biological Journal of the Linnean Society 19: 115-129). The factory was a significant source of local particulate air pollution and Lees & Dent found a strong relationship between the combined melanic morphs in the proximity of the factory. Over 98% of the insects were melanic immediately adjacent to the factory and declined to normal proportions for South Wales 1.5-6 km depending on the direction. The melanic frequencies were far higher than any found elsewhere in the species range in Europe, Asia and North America. It was suggested that the relationship was due to the selective effects of the local air pollution from the factory. It was not clear if selective predation, direct effects of pollution or thermo-regulation are the factors involved in the prevalence of melanic forms.

This change in melanic frequency (reported in 1983) occurred in less that 40 generations since the factory was first operated from 1942 (and expanded from 1951-1968). The factory was removed around 20 years ago. What would be the proportion of melanics at the original sites some 20 years later? A similar relationship was also found in the Cardiff Docks area. With the benefit of a Nuffield Science Bursary to Jenny O’Neill, a second-year student from Cardiff University, we have this past summer sampled from as many of the original sites both in the Cynon Valley and in the Cardiff Docks. Preliminary results, based on evaluation of over 8000 specimens from around 50 sites show that percentages of melanic morphs have decreased from the peak of 98% to around 50%. Full results are under analysis.

So, it seems that as air quality has improved, the advantages of being a dark coloured spittlebug have similarly declined. It is a fascinating study. If you have the chance go and see the display in the Museum with shows examples of the normal ‘light’ coloured bugs and the ‘darker’ Abercwmboi ones.