Thread subject: :: Let's see if I'm learning, Eristalis tenax?

Posted by Andre on 06-11-2005 16:17

Like kahis correctly says, it's not the hairs on the fore-head that is used to determine this species. It's the two "thicker" rows of vertically growing hair-bandes on the eyes (in fact, it is where the hairs on the eyes grow more dense than elwewhere on the surface of the eyes).
One of these rows (or bands if you like) shows clearly on this picture.
What we also check is the color of the tarsae of the forelegs. In this picture not visible. If the tarsae are all yellow, we know directly we are dealing with the species Eristalis pertinax. Comes quite handy when other feateres don't show well... Anyway.... this was a sidestep.
How we see if it is a male or a female: in Eristalis the eyes of the males reach eachother, while the females are dichoptic which means the eyes are clearly seperated by a broad part of the forehead (the frons).
Because of the fact that in males the eyes meet on the forehead (above antennae) there is only a small, triangular space left on the head just above the eyes.
There are quite some diptera-families where same features appear as a matter of fact. Just be aware of the exceptions though, 'cause there always are exceptions.... that's nature! ;)