Well, I have three pairs together. Mustard Gas, Yellow Butterfly and Blue Butterfly. I let them go at about 1PM, and as of 6PM, there are eggs ALL OVER the Mustard Gas tank. I did not see them spawn, and the female still has a lot of eggs left in her. I don't know if they spawned, or if she's just dropping eggs. Both male and female are picking eggs up and putting them wherever they feel like it on the surface (which makes me think they are indeed fertile), but they are mostly sinking back down to the bottom.
The Blue Butterfly pair is getting very close, and the Yellow Butterfly pair is thinking sexy thoughts.
The Mustard Gas male is, so far, a lousy daddy. He spits the eggs into a non-existent nest, and then swishes them away as he turns to get more. He is clueless The eggs are all over the floor, looking like it has snowed.
The other two couples have decided to wait until tomorrow.
The Mustard Gas dude was just sitting around looking bored, so I took him out. I put all the eggs in a cup with an airstone, immersed in the tank to keep it heated. As of ~20 hours, I don't see any sign of development in the eggs, but there is also no fungus. I'll let them go and see what happens.
The female was really ripe, so I think she just dropped eggs due to the excitement.
Yesterday I put my three pairs back together. Everything seemed to be going amicably, but I woke up this morning to find that the blue female had killed the steel blue butterfly male some time during the night.