Pearl-bordered and Small Pearl-bordered
Fritillaries have contrasting fortunes in Cumbria,
despite sharing the same foodplants of Common Dog
Violet and Marsh Violet, plants
that are found in almost every tetrad within the county.
Pearl-bordered Fritillary (above) is the
first fritillary to appear in the year and is usually on the
wing in Cumbria from about the end of the second week
of May. The Small Pearl-bordered Fritillary
emerges about a fortnight later and its flight period covers
the whole of June. There is therefore an overlap
between the two species that can make identification difficult.
Pearl-bordered has declined both locally and nationally;
it is now almost entirely restricted to the limestone areas
at the head of Morecambe Bay, for example Arnside Knott and
the Whitbarrow area. There are probably now no more than 15
or so colonies in Cumbria, but that comprises around 10% of
all the colonies remaining in the UK.
Small Pearl-bordered is widespread throughout
the county with the number of colonies probably numbering
over 200. As well as grassland sites, where it can be found
alongside the Pearl-bordered, it is more likely to be seen
on its own as it can make use of much wetter areas, for example
along the wet edges of woodland and in marsh areas besides
streams and rivers where trees don't grow (and where Marsh
Violet is likely to be the main food plant).
Small Pearl-bordered does look smaller (just!) but has a generally
duskier appearance. On the upperside of the wings
the orange is deeper (when fresh) and the black more pronounced,
the black being noticeably dense around the outside edges
of the wings. The underside of the wings (above)
seem more contrasty as there are several silver areas on the
forewing whereas the Pearl-borded looks more overall yellowish
and has only two silver patches (one large and one small).
species overwinter as the partially developed caterpillar.
As the Pearl-bordered needs to grow fast in the spring for
its earlier pupation and emergence in May, it needs a very
warm micro-climate. This is provided by dead bracken and dead
leaves which absorb the warmth of the spring sun reflected
by the limestone (as below). However, the layer must not become
too thick otherwise violets will not grow. The species also
rapidly declines if tree cover builds up and light is excluded.
Limestone pavements provide ideal conditions for both the
Common Dog Violet and the butterfly, as pockets of dead material
are trapped between the rocks where the violet often grows.
Small Pearl-bordered has less demanding requirements and has
longer to develop as its flight-time is later. There are plenty
of open, but sheltered, marshy areas in Cumbria receiving
good sunlight and which also have light coverings of dead
the neighbouring county of Durham has only a handful of colonies
of Small Pearl-bordered Fritillary.