Cheers! You're right about the etherial stuff - another way to get them is to get mind probes + excess stun weapons (just in case) and fly off to the FIRST terror site. It will most likely be nothing dangerous, especially if only Floaters are involved. Just capture literally EVERY alien at the site of any importance (one soldier with a mind probe in your skyranger WILL be able to 'read' anything in the whole map) or just fire stun launchers and throw smoke grenades/use stun rods all over the map just to make sure.
I think that the 'reproduction' is used in that VERY nasty corrosive venow, not in the Battlescape.
*edit* Get loads of medics, navigators and engineers. Then you are given something handy no matter what.