While we were discussing this topic, I questionned Torben Larsen, and here is his answer which he authorize me to reproduce here :
Torben B. Larsen wrote:
"I was first presented with the picture of this "species" by John Riley and Mike Cornes during my first visit to Nigeria in 1967. None of us had ever seen Papilio antimachus or P. zalmoxis in nature. My view then was that it was a case of "too much tropical sun". Much later I learnt that its observer, T.A. Barns was actually a very astute and reliable man, who collected many new species during his amazing trip by car up the Albertine Rift Valley from Congo to Uganda. However, I ruled out in my mind that it could be a hybrid between the two giant species, though Papilio hybrids are not all that unusual. However, a pattern on forewings of one species [zalmoxis] and hindwings of another [antimachus] does not seem to occur in butterfly hybrids. The blue colour in P. zalmoxis is based on very special "Tyndall scales" colour refraction" and such scale structures would hardly be inherited on one set of wings, but not the other, in a hybrid. It would therefore have to a genuine unknown species. Though both species may be difficult catch, they do hill-top and visit damp patches. It seems difficult to believe that by now such a butterfly has not yet been collected again – even local commercial collectors would know that such a butterfly would bring in even more money than the two others. I have never met with P. antimachus in nature, but in 1997 I did see quite a few P. zalmoxis during a butterfly survey in the Oban Hills National Park in Nigeria. When looking for suitable drinking spots they circled, swooped up and down, and often made sudden abrupt turns. In these circumstances it was often possible to see the brown undersides of the hindwing and the blue of the forewings, or parts of them, at the same time. I wonder if it was not this type of view that led to Barns' drawing."
Michel. Many many thanks for contacting Torben - I loved his Hazards of Butterfly Collecting book, it has become a firm favorite of mine and many others I believe. Very interesting to hear his views, it would be a real honour if he did indeed participate here.
The venerable Torben Larsen was quoted by Michel: "In these circumstances it was often possible to [see] the brown undersides of the hindwing and the blue of the forewings, or parts of them, at the same time. I wonder if it was not this type of view that led to Barns' drawing."
This is exactly what I had in mind when I commented on page 2 of the thread "I do think though that he really did see something, maybe an aberration, a hybrid or an unknown species. My only major doubt is that if he was in a canoe on the river how much of the upperside of the butterfly did he actually see. Maybe much of the pattern is actually based on the underside."
Peter, I actually pointed out the "hand written note on the report about the drawing stating that Pomeroy actually caught one in 1913 at Ossidinga, Congo, but the collection was lost in transit" in my 3rd reply on page 1 of this thread. I guess you may have missed it in all the excitement. This has been a really interesting thread, and thank you very much for all the work you put into the original report on Barns' travels.