May 2013 Blog
The two main species to look out for this month the Pearl-bordered and the Small Pearl-bordered. Right away you will be thinking if one is smaller then it will be easy, no, the size difference is miniscule. The upper wing surfaces of both species are a shade of orange with black markings. The pattern, not the colour, is similar to that of the Snakes Head Fritillary flower after which they are named. The main identification feature is on the underside of the wing. Unfortunately this is part of their anatomy that they don’t show very often, but with time and patience, something every wildlife watcher should have, you will be rewarded. The Pearl-bordered has a row of spots across the middle of the underside of the hind wing; these are all yellowish except for the middle one of the row which is a silver/white. Whereas with the Small Pearl-Bordered the row is almost completely made up of silver/white spots. Easy! Both fly in spring and summer, the Pearl-bordered in May and June and the Small Pearl-bordered in June and July. So just now you could easily come across either or both together. Both species frequent similar habitats, woodland glades, open forest rides and damp heathland where they search for nectar on plants such as Thistles, Bugle etc. The Small Pearl-bordered often preferring the wetter parts of these habitats.
Both species are of conservation concern and have declined in many areas. There is however work being undertaken by the various conservation agencies to halt this, mainly through habitat management. In particular the Forestry Commission at Mabie Forest. Both species cannot survive without one very important ingredient, Violets. They will only lay their eggs on this species of plant and where areas have been managed for violets in particular these species are doing well. The eggs will hatch in 10-14 days and the caterpillars will start feeding and growing immediately. As they grow they will moult their skins three times within the next 5-6 weeks. Each caterpillar then finds a shrivelled up leaf at the base of a violet plant in which to pass the winter. The following spring the caterpillar will emerge, having shrunk to half their size during hibernation ready to start feeding on the new growth of the plant before pupating, a stage which will last around a fortnight before emerging as an adult to start the cycle all over again. They both only have one brood per year.
As both adults look the same, and are found in the same habitats, at the same time, it was thought many years ago that they may interbreed, but they don’t. This means they must have some way of telling each other apart that does not involve looking at the underside of the wing, because when they are active their wings are open. If you spend any time watching them you’ll notice they always divert from their flight path to investigate another fritillary sunning itself on a flower close by. It appears sight including colour vision plays a part in the recognition process. However males have special scent glands on their wings and it seems at close quarters scent is more important than sight. The females can identify the scent of the males of their own species and so find a suitable partner.
Thanks for looking.