I was thinking about doing this episode having lunch outside one day, and bemoaning the fact that I didn't have any pictures of these guys that I could publish on the blog.   At that moment a bibio that landed on the table in front of me.   Of course I was too discombobulated to get a picture before it flew off - but I saw that as a good sign to do this episode.  

But that said, there are plenty of pictures of these guys on the interweb.   For example, here:  https://www.inaturalist.org/observations?place_id=any&taxon_id=56097&verifiable=any As you can see, there is a fair bit of diversity, but note the black or black and red color, the long abdomen, the wings held flat over the body, and the dangley legs.   In terms of patterns, one of the old ones I really like is as follows: 

• Hook: Size 12 or 14 wet fly hook
• Body: Ostrich herl (or hair from the ear of a black spaniel)
• Wings: Pale Starling slips (or duck, this is starling, altho I've also seen pigeon)
• Hackle: Black starling, or hen hackle

I would bet a leadwing coachman would also be a great imitation.    Next is an imitation from New Zealand of a Blossom Fly - 

Again, pretty straightforward: 

• Hook: 12-14 dry fly
• Body: Peacock Herl
• Rib: Black Cock
• Hackle: Black Cock

And this pattern from Malcolm Greenhalgh: 

• Hook: Dry Fly 12-14
• Body: Black Floss
• Rib: Peacock Herl
• Wing: Dun hackle tips
• Hackle: Black cock

And this one, which I like because it imitates the dangly legs:

• Hook: 12-14 dry fly
• Body: Black dyed pheasant herl (or goose)
• Hackle: Black cock
• Legs:  Black dyed pheasant herl tied back. 
• Or you can do the Fore and Aft:
• Hook: 12-14 dry
• Hackle: Black cock at hook bend
• Body: Thread
• Hackle: Black cock at eye.

As you can see, these are all fairly straightforward flies.