Do you get hornets in your part of the world? I don't think we do down here very often.
I've never seen one, but Tricia has just said she was almost scared out of her skin by one when it appeared beneath her nose when she was staring out of the window once in Burry Port!
Can't help thinking that the "gwenynen, cacynen, picwnen" thing is probably one of those things that doesn't map perfectly onto "bee, wasp, hornet", being used differently by different people in different areas! (As you know, and were saying, really, anyway, of course!)
I think (and am a bit embarrassed to admit) that this is the first time I've used the word "hornet" in the wild in a natural conversation in English, let alone heard it in Welsh, so good to know what you would use!
(Note to self- get out in the wild a bit more.........)