Pete Eeles wrote:Hi Jerry - this is definitely
ab. ocellata - based on the 3 butterfly "variation" books I have (Frohawk, Russwurm and Harmer). And as suggested by Piers (Felix) in another thread.
nigricans seems to be reserved for especially-dark individuals. However, there is a point at which the distinction between the two isn't clear-cut. Adrian Hoskins has a photo of another aberration on his excellent website at:
http://www.learnaboutbutterflies.com/pa ... 20001d.jpg
which he has down as
nigricans. This individual is right on the "border" for me, between
nigricans and
occelata and, based on the books I have, would have put down as
occelata myself. But it's not an exact science by any means.
Cheers,
- Pete
Pete is spot on with this Silver Washed Fritillary aberration: while this is a particularly extreme example it is certainly an
oscellata as the diagnostic features of
oscellata (markings extended to form lozenge or 'eye' shapes) are still clearly visible, where as the determining feature for
nigricans is an almost entire suffusion of black scales (with the exception of the base of the wings and the fringes), completely obscuring the usual markings. This specimen is an extreme
oscellata.
This years aberration 'event' in Silver Washed Fritillary last occurred on this scale in 1976. Prior to that, other 'paphia years' were 1941/42, 1918/19 and 1881, strangely this occurrence seems to happen at 30 year intervals. Could this be linked to a climatic cycle or is it just pure coincidence?
Aberrations are usually caused by one of four factors (or a rarely combination of two or more): Environmental influence, for example extremes of temperature during the early pupal stage; a recessive gene, for example
tithonus (the blue female) in the Chalkhill blue; pathological where the insect does not form correctly (the white winged Ringlet being a superb example where an area of the wing lacks pigmentation); and homoeosis, where an area of one wing is 'reproduced' like a curious patchwork on a part of another wing. An example of this could be where an area of upper side pattern and colouration of a Fritillary appears in a 'patch' on the underside of the hind wing. Homoeosis is however very rare in butterflies.
Aberrations are usually named according to the features that make them different from 'type', for example in
oscellata where the normal markings are extended into 'eye' shapes,
confluens where markings extend and join,
radiata where spots extend outwards to form streaks or bars,
caeca where the markings are absent (caeca means 'blind') etc.
Aberrations are sometimes named after the individual that first described them (the Chalkhill Blue ab
Fowleri being an example) or rarely after the location at which the aberration was first recorded (the Purple Emperor aberration
Chattendeni was first recorded from Chattenden).
Aberrations are fairly finite. Although new aberrations that are as yet undescribed do at times occur, the majority have been described and named. Some species are more variable than others: in Britain the Chalkhill Blue has 446 named aberrations, the Silver washed Fritillary 47, the Painted Lady 32, and the White Letter Hairstreak a humble 7.
When identifying an aberration it is worth looking for what is different about the specimen and what remains the same; what features have altered and how. That way it is possible to narrow down the possibilities. This is how Pete was able to determine that the Silver Washed Fritillary aberration photographed by Adrian Hoskins was
oscellata and not
nigricans.
I could waffle on for hours and in great detail about this subject but I am not very quick at writing or typing (at least not in a way that makes any sense!), and (for those that are still reading) I have probably gone on and on and on enough!!
Felix.