The mutatioin that makes them wingless is easily reversed, which is where I think the problem is. I was very careful with mine, every time, but eventually, one will hatch with wings and that becomes dominant, so it was off to the races.
I always kept six bottles going so I could toss any with wings in there. I was told, but never followed up, that winged forms are more common when they are kept warm. I had more trouble in summer, but I also had more chance of a winged one sneaking in despite my caution, so...
I always kept six bottles going so I could toss any with wings in there. I was told, but never followed up, that winged forms are more common when they are kept warm. I had more trouble in summer, but I also had more chance of a winged one sneaking in despite my caution, so...