I have not had a problem with the biots coming apart or tearing ( and I tie a lot of biot body flies)...this article is a good guide for tying with biots:
http://flyanglersonline.com/flytying...ps/part102.php
Here: are split case patterns that can be applied to Baetis/ BWO's that are tied by two friends:
http://www.mkflies.com/page2.php
http://stevenojai.tripod.com/splitcase.htm
And Greg Vinci ties the "Crack Back Baetis" which is another approach to this stage of emergence...
I'd link, but the site is down for reconstruction...
PT/TB