[Kajazy]

A simple question (but can't find the answer on Google!) - how big is the adult carrot fly? I saw a conglomeration of black flies trapped UNDER  my insect mesh over my carrots today.... They were quite big (about 3/4 inch), black, winged and a bit dopey...

[AnneB]

They are smaller than that - black, glossy and about 5mm long - so you'd get about 5 of them to the inch.

Measurements from Which? report on carrot fly

http://www.which.co.uk/documents/pdf/carrot-fly-151760.pdf

[AnneB]

So if bigger ones got in, so can carrot flies.....

[Fisherman]

So if bigger ones got in, so can carrot flies.....

I think its more likely that they couldn't get out rather than they couldn't get in. If you cover an area with mesh various flies will emerge from the ground hence the reason for crop rotation.

[bazh]

A simple question (but can't find the answer on Google!) - how big is the adult carrot fly? I saw a conglomeration of black flies trapped UNDER  my insect mesh over my carrots today.... They were quite big (about 3/4 inch), black, winged and a bit dopey...

I was digging over a previously undug area of my plot on Friday and came across something that sounds exactly like your describing haven't got a clue what they were though sorry    wondered at the time and knew I should have took a photo, looked a bit like flying ants but bigger and very dopey looking just moping around, definately not carrot fly though.

[Kajazy]

That's exactly it - similar looking to flying ants but bigger. Well, thanks all for at least putting my mind to rest that it's not carrot fly. I'm pretty sure they hatched out from the soil - there were so many of them, and all in a cluster, and the sides of the mesh were pretty secure. Must be related to all the rain we've had...

[Salmo]

I have never seen a carrot fly but I understand that they have yellow legs.