Male mollies behavior on Females after having babies.

Question
I have a 20 gallon aquarium which is set up with an undergravel filter and exterior filter.  It has been set up for over 7 months, I vacumm the gravel every month and half and change out hal the water. I currently have a crab, placustumist, and four couple of mollies (black, orange, silver, and red/black).  My silver mollie had babies, I seperated them, then my orange mollie has had babies twice, but after the second time, all the male fish are constantly following her and nubbing on her bottom fin. Is this normal mating behavior or can they cause harm.

Answer
Hi Victor;

Male mollies live for two purposes; Eating and breeding. Sometimes they can't seem to stop trying to breed even to eat! They use the opportunity of the females coming to feed as a chance to breed again. Especially "amorous" males like that can harrass a female until she is so sick she dies. It's important to keep extra females with males like those. The minimum ratio is two females per male. It helps distribute their attentions more so all the females can get rest. It also helps to provide plenty of hiding places for them. Visual barriers aid in the females' peace and quiet as they need it.

At Your Service;
Chris Robbins