Having searched under Fritz Heckert , I haven't seen any jugs with applied snakes yet. I had hoped that it might be a known Petersdorf Glassworks jug shape (with or without the snake).
The flying insects have such a distinctive style though , almost cartoon like , there must have been only one decorator who would have painted bugs like that (surely ?) unless they were applied as some sort of transfer to the glass originally rather than painted directly onto the glass from scratch.....but I have no idea about enamelling techniques. The bugs must hold the key to finding out more
It's a shame there isn't more detail on the Mike Weedon tumblers in the link above...I can't see any legs on the insects (there is a dark area behind where they might be though) !! I wonder if the tumblers were signed ?
I will have a look at Yahoo.de , see if anything comes up ! Good Luck !