A quick glance at on-line photos shows that the same red lines are regularly seen in both male and female balteatus. So we can deduce that they are not associated with the reproductive organs. Dissection is probably the best way of determining what they are. Malpighian tubules are a possibility. From what I've read, at least some flies have substantial paired tubules, but I've no idea what they actually look like.
Interesting. I assume that we should see signs of these anatomical internals in other hoverflies, at least those with sufficiently pale bands on the abdomen for them to be visible. Would you agree?
I'm not sure how much variation there is in syrphid internal anatomy. I did have a look at on-line images of Syrphus, and couldn't spot any that had the red lines, so either their yellow patches are not as translucent, or they have different internal anatomy. Bearing in mind that there are lots of Episyrphus without the red lines, I think detailed anatomical investigation is the only way to understand what's going on. Could be an interesting project if you have the time and a steady hand.
Thanks, Tony, that makes sense. I have repeatedly swept the species over deer corpses, so it must work for them!
Ian
Yes, Collin, you are right. The lack stigma spot, the strong markings on the sides of the thorax and the broad black mark on the head identify this. There are similar in markings to N submaculosa and the males have a different inner clasper. I don't know if the females have similar ovipositors or not. N flavescens is common and I get it in my garden.
John Kramer
Yes, correct Colin. The dark seam across the wing is diagnostic. At the moment this is a commonly recorded cranefly.
John K
That's right Colin. The club-shaped appendage at the rear is diagnostic of the male. What is the habitat like at Witt's End ??
John K
Yes. Correct. Good to check the genitalia as well. Nice photo !! You never know, one day you might get a new species !!
John K
Thank you John. Witts End is a conservation site. Old arable fields left unmanaged for about 15 years. So rough grassland with flowering herbs, surrounded by hedgerow with a few mature oak and willow trees. Wet ditch/stream? along one side, which is where specimen was found. SP992324.
It's hard to tell from your picture, but I think this could be L. lutea. Are you sure about the anteroventral on the distal half of the middle tibia (couplet 1)? Also the verticals are pale yellow in L. bifurcata, and yours look rather dark.
Choerades marginatus