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Index of Subjects
Index of Subjects Hi Chris, Angus, As I think I mentioned before, the eyes in many flies (but certainly not all) are sexually dimorphic, and always in the same direction as far as gender: males are "holoptic" with eyes that meet (or run close together) at the midline, while females are "dichoptic" with the eyes apparently separated at the midline. 'Apparently' means that the female eyes are not really further apart, but actually lack a piece of eye at the midline that the males possess. This specialized male-specific zone is used specifically for imaging females and rival males, and chasing them, where this has been investigated behaviourally using high speed cameras and mirrors (houseflies). All the syrphids I've seen here are sexually dimorphic like this, and some UK syrphids also have been investigated regarding this chase behaviour. So the picture that Chris IDd as the slender Meliscaeva is a female, while the plump Eristalis is a male for sure. Steve *********************************** Quoting Christopher Majka <c.majka@ns.sympatico.ca>: > Hi Angus, > On 25-Sep-06, at 11:21 PM, Angus MacLean wrote: >> Thanks, Chris. Perfect match for the abdomen but as you state, this >> doesn't always have to be exact. The "frons" does not match with >> the fly in my photo, obviously another feature that variable. > > The frons of the specimen in the first photo looks to be a close > match to that of yours, while the individual in the second photo has > a much narrower one. It could be a difference between males and > females. I don't know enough about flies to hazard a guess. > Cheers! > Chris > _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._. _. > Christopher Majka - Nova Scotia Museum of Natural History > 1747 Summer Street, Halifax, Nova Scotia, Canada B3H 3A6 > (902) 424-6435 Email <c.majka@ns.sympatico.ca> > _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._. _. > > Here's another Hover Fly with a beautifully marked abdomen. http://www.flickr.com/photos/58321572@N00/250842872/ Another Hover Fly I uploaded earlier was thought to be a Eristalis spp. but this one although somewhat similar, I believe is a Metasyrphus spp., perhaps americanus although the latter has brighter yellow striping on the abdomen. The Eristalis spp. can be found at: http://www.flickr.com/photos/58321572@N00/228628774/ Comments are appreciated. Angus
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Index of Subjects