1931 Biston betularia (Peppered Moth)

Geometridae, Ennominae Wingspan: 44-56mm.

A common larger and distinctive species throughout the UK, and widespread in Cornwall. This species is, perhaps, interesting in so far as it became an indicator of industrial pollution, as two forms became known. The above form shown here is the normal individual, but in the 20th century, as industrialisation increased in the central areas of the UK, this form stood out against sooty surfaces, so was predates easily. In these areas, a melanistic form (B.b.carbonaria) which was black, with a few small white spots became the most common form, blending better with the backgrounds, showing the effects of natural selection occurring. Nowadays, as pollution has been drastically reduced, the more normal form has re-appeared again in these areas. It may be that they are now hedging their bets, as a further form (B.b.insularia) not connected to the melanism has appeared in populations which is about half-way between the two extremes. These variants are unlikely to be found in Cornwall.

The flight season of this species is quite wide, quoted in the UK as early May to late August. In Cornwall, individuals can also be found in April, and occasionally as late as September / October.