gorganus or britannicus?

[MikeOxon]

In view of the recent Sussex sightings, perhaps it's time to resurrect this thread! There are several topics in Neil Hulme's PD that could usefully be aired here.

Looking back over this thread, it seems that positive visual separation of britannicus and gorganus is not as simple as has sometimes been assumed. I can foresee identification becoming a real problem if the new arrivals start to spread.

Mike

[Pete Eeles]

I think location will be the initial and primary indicator of whether a Swallowtail is gorganus or britannicus, and we'd have to see gorganus sightings coming from Norfolk before we'd need to take a closer look.

Cheers,

- Pete

[NickB]

The one possible difference I have noted is that the red & blue spots at the base of the hind-wing appear to be more oval than circular in ssp. britannicus......

[NickB]

I think location will be the initial and primary indicator of whether a Swallowtail is gorganus or britannicus, and we'd have to see gorganus sightings coming from Norfolk before we'd need to take a closer look.

Cheers,

- Pete

Last year we had reports of Swallowtail from Essex; id from photos was inconclusive....

[Pete Eeles]

I think location will be the initial and primary indicator of whether a Swallowtail is gorganus or britannicus, and we'd have to see gorganus sightings coming from Norfolk before we'd need to take a closer look.

Cheers,

- Pete

Last year we had reports of Swallowtail from Essex; id from photos was inconclusive....

I think release of captive-bred individuals could contribute to the confusion - but I'm not sure if there's ever been a confirmed sighting of britannicus outside of the Norfolk broads.

Cheers,

- Pete

[Pete Eeles]

The one possible difference I have noted is that the red & blue spots at the base of the hind-wing appear to be more oval than circular in ssp. britannicus......

I think the descriptions of britannicus (in terms of differences with gorganus) are pretty good - see http://www.ukbutterflies.co.uk/species. ... es=machaon

1. It has an overall darker appearance. The submarginal bands are particularly broad and dark in comparison.
2. Ford (1945) states that, on the hindwing, the submarginal band, marked with blue, extends nearer to the dark mark at the end of the cell.
3. Ford (1945) states that the ground colour is of a deeper yellow, giving ssp. gorganus a lighter appearance, although this difference is disputed by Cooke (1946).
4. Ford (1945), Dennis (1977) and Riley (2007) state that, unlike ssp. gorganus, the submarginal bands are triangular, being wider at base of the wings and narrower at the apex, while this band is not so tapered in ssp. gorganus.
5. Riley (2007) states that ssp. britannicus is slightly smaller than ssp. gorganus.

Cheers,

- Pete

[NickB]

I think location will be the initial and primary indicator of whether a Swallowtail is gorganus or britannicus, and we'd have to see gorganus sightings coming from Norfolk before we'd need to take a closer look.
Cheers,
- Pete

Last year we had reports of Swallowtail from Essex; id from photos was inconclusive....

I think release of captive-bred individuals could contribute to the confusion - but I'm not sure if there's ever been a confirmed sighting of britannicus outside of the Norfolk broads.
Cheers,
- Pete

I agree Pete; tho' being within 30 miles of known britannicus sites........

[MikeOxon]

I'm not sure if there's ever been a confirmed sighting of britannicus outside of the Norfolk broads.

But, I quote from the Ouse Washes Landscape Partnership Scheme (http://www.cambsacre.org.uk/downloads/o ... 080933.pdf ) "New fenland habitats are being created to encourage a number of high priority species including otter, water vole, bittern, bearded tit, marsh harrier, black-tailed godwit, fen violet and swallowtail butterfly."

Mike

[Padfield]

British swallowtails come from a relatively small gene pool in a narrowly defined geographic area. They mostly resemble the description of a 'typical' British swallowtail quite closely. Continental swallowtails (those designated 'gorganus' - because there are of course many other subspecies globally) come from a vast gene pool in a population extending from central and/or southern Europe (depending on the authority) to central Asia. There is considerable variation among them. Some have tapered submarginal bands, some parallel, some are large, others smaller, &c. &c. I've seen individuals that would not look out of place in the Broads as well as some you would immediately unmask as impostors. So while you can often say, 'That's not britannicus', you can rarely say with certainty, 'That is britannicus'.

If we assume the visitors are all from the same general source population (which might or might not be a fair assumption), perhaps rather than looking for generic 'gorganus' characteristics we should be looking particularly at the distinctive features of those immigrant butterflies photographed in the UK, whose offspring or great-offspring might ultimately check out the Broads.

Guy

[Neil Hulme]

I think the situation is very much as Guy suggests and that the diagnostic descriptions reiterated by Pete will hold true in the majority of cases. The majority of individuals will probably be identifiable as either gorganus or britannicus. My images show what I believe to be very typical males of both subspecies .... easy(ish)! However, I'm equally sure that natural variation will allow for relatively small, dark examples of gorganus, which will be almost impossible to call with confidence. This could get interesting!

gorganus

britannicus

[NickB]

I'm not sure if there's ever been a confirmed sighting of britannicus outside of the Norfolk broads.

But, I quote from the Ouse Washes Landscape Partnership Scheme (http://www.cambsacre.org.uk/downloads/o ... 080933.pdf ) "New fenland habitats are being created to encourage a number of high priority species including otter, water vole, bittern, bearded tit, marsh harrier, black-tailed godwit, fen violet and swallowtail butterfly."
Mike

Here in Cambs. we are aware of the intentions of the various bodies to possibly re-introduce britannicus where it used to be before the Fens were drained in the 1850's, after the introduction of steam-powered pumps. Previous attempts at Wicken Fen ultimately failed, as water levels were not easily controlled and the area was possibly too small to support a viable population. The "Great Fen" http://www.greatfen.org.uk/ project also states that britannicus is a target for re-introduction; we shall see....

[David M]

As others have said, if you're outside Norfolk then you can readily assume it's gorganus as, to my knowledge, britannicus has not been recorded much outside of its stronghold for a considerable number of years.

What WOULD be interesting is if the continental race 'invades' East Anglia.

[Pieter Vantieghem]

Is there a Friesland (northern Netherlands) equivalent fenny race to our britannicus? I ask because it might have evolved when the North Sea was dry land but at the end of the last Ice Age, the populations became isolated.

If there is a Dutch fenland race, then conceivably vagrants of this race might occasionally reach eastern England.

Jack

In fact the species is quite rare in Friesland and sightings probably refer to strays from more south. See the dutch site: http://www.vlindernet.nl/vlindersoort_v ... ginnenpage