Part 7: Butterflies and other insects

 

British Swallowtail

With the exception of beetles, whose tough exoskeletons are often preserved, insects do not often fossilise so the insect fauna of Britain is mostly speculative. In most ways it probably resembled the modern fauna, although the slightly warmer summers and more seasonal climate might have meant that it had more in common with central and western France than it has today. One way we can determine the structure of the habitat is from those beetles, as they are quite specific in their habitat requirements. The high incidence of certain types of dung beetles indicates that the British landscape in many areas was open countryside with large numbers of large herbivores shaping the habitat – the picture of primeval Europe being one vast forest is itself unnatural and is probably a consequence of the extinction of megafauna across the planet at the end of the last glaciation.

Many insects are migratory, and no doubt Painted Lady, Red Admiral and other butterflies made annual visits to Britain for the summer before migrating back south in the autumn, just as they do today. Dragonflies are also long-distance migrants in many cases, so the beaver and hippo- created wetlands would have swarmed with them as well. Without pollution, mayflies would likewise have swarmed over the water providing ample food for insectivorous birds.

Britain has very few endemic insects but they include our largest and most specialised butterfly, the British subspecies of the widespread Common Swallowtail Papilio machaon. There are several species across Europe, and the mainland subspecies sometimes migrates into Britain and even sometimes breeds (Swallowtails are strong flyers and the mainland form feeds on many plants in the carrot family). The British form however is highly specialised for feeding on a single foodplant – Milk Parsley- and this only grows in marshy areas. This specialisation cannot be a recent development since the end of the last glaciation so presumably the original habitat was the extensive marshland where the North Sea now covers the land, and in the Eemian it might well have been widespread across the wetlands of southern Britain. Milk Parsley needs to grow to a large size before it becomes attractive to egg-laying females, and a specific reed-cutting and grazing regime is needed to maintain the habitat it optimum condition in the few sites it still survives. In the past grazing by large animals, occasional fires, and more extensive wetlands would have made its survival much less of a problem,

Large Copper

Using the same habitat would have been the Large Copper, whose native British subspecies is now sadly extinct. Attempts have been made to reintroduce the continental form, but with limited success.

Scarce Swallowtail

Another swallowtail butterfly found in Europe is the Scarce Swallowtail, which got its name from rare specimens obtained by early collectors in southwest England. These may have been a tiny surviving population or recent immigrants, but in the Eemian they might well have been widespread as the larvae feed on many common and widespread species of Prunus, Malus and Crataegus among other plants. With a similar range of foodplants the Black-Veined White, formerly native to the UK but now only found on the continent, would have also been found on the edges of woodlands and in scrub.

Purple and Lesser Purple Emperors feeding

After the Swallowtail, Britain’s largest extant butterfly is the Purple Emperor, but they might well have been joined by its only slightly smaller relative the Lesser Emperor. This continental species favours damp woodlands where poplars (its main foodplant) grow. Both these species are well known for being attracted to animal dung, so the territorial middens of rhinos and piles of elephant dung would have been a magnet for them.

Camberwell Beauty

The more seasonal climate would have made Britain much more habitable for what is now a rare immigrant to this country, the large and impressive Camberwell Beauty (known as the Mourning Cloak in the US). The butterfly was named from where it was first caught by an early collector, but all those seen in the UK are the result of individual hitching a lift with imported wood from the continent.

The Glanville Fritillary has a toehold on the south coast today and might well have been more widespread in the south given the more continental climate.

Among moths, the habitat would have been ideal for those that love flowering meadows such as the various Burnet moths, and various hawkmoths like Broad-Bordered Bee Hawk would have been far more widespread than it is today.

This completes my survey of Eemian Britain. Next time I will look at the consequences of these discoveries for conservation and rewilding in Britain today.