Hi David. Several years ago I found that longer legs on my beetle imitations brought more "takes". I fiddled for a bit tying longer and longer legs on the same size beetle body. I made a number of flies with legs that were two, three, even four times longer than patterns available from commercial sources. Fishing them together on a tandem or even triple fly combo, I noticed more strikes on the longer legs. On rare occasions I even had a rising fish switch in mid rise from one beetle to its longer legged partner. Not a scientific study for certain but I do tie longer legs on most of my beetle patterns. Besides, you can always trim them downwards if needed.
I agree with bill on this. However when it comes to the stonefly or girdle bug here I like to cut my tail antennas down more than the rest of the legs. I also try to taper the legs on the abdomen from longer to shorter from head to tail. I also like the legs on the first 3/4 of the body. That being said I don't think it really matters that much and that's one fishy stonefly!
On FlyFlasher.com you can find 34,433 flies from all over the world. Flash your own fly patterns, upload your current work or search for inspiration. The flies are tagged, so you easily can search for them.