Clouded Yellow: This is a ‘white’ and so is closely related to the Large and Small Whites, Orange Tip and Brimstone. It is another migrant that, while it breeds over the summer in the UK, fails to over-winter except in very small numbers along the UK’s sheltered south coasts – the Isle of Wight and Dorset. As with the Painted Lady its permanent population is in North Africa and Southern Europe. Each year very variable numbers head northwards spreading out across Europe and Asia. They usually arrive in the UK in late May. The food plants of the caterpillars are members of the Pea family, particularly Clovers and Lucerne. In good years they can produce three generations but more usually two with adults appearing in August and then again in October. There is evidence of a return migration but not in the ‘clouds’ in which they can arrive in good years. The last ‘Clouded Yellow year’ was 2013 but they only appear in Westbury Gardens very occasionally and in most years not at all. The most likely place to see them in the Parish is on the top of the Mendips nectaring on knapweeds and scabious before flying onwards. It could be that there is limited growth of the fodder crops, Clover and Lucerne, locally, and so there is little opportunity for numbers to build up nearby, even in years of abundant immigration.
The butterfly is Small White sized but of more sturdy build and is a very strong flier being able to cross long distances over the sea. The typical form is a very distinctive golden yellow but about 10% of the females are a much paler yellow – called ‘helice’. These can easily be confused at a distance with brimstones and the other whites but the heavy dark markings around the edges of the wings are diagnostic. However, when the butterfly settles it almost always settles with wings closed so it is rare to see these distinctive upper surfaces except in flight.
Photos John Ball