Draco is 11 years old and has been neutered since he was 2. We got Tiger Lily 3 months ago at 4 months. She was spayed a month after we got her. All of a sudden Draco is trying to mount her. He bites the scruff of her neck and holds on while he try
It's to get on her. We have a 1-1/2 year old calico female that we have had since she was a kitten and is spayed and he has never done it to Pixie before. Any thoughts?

It could be asserting his dominance over her. He might have never done it to your other cat because other body posturing did the trick in establish pecking order or happened when you weren't around to see how effective it was. As some of our fur family were reaching sexual maturity, even though have been neutered, the boys jostled for pecking order again often doing what you describe when body posturing wasn't enough. Food for thought. I'd recommend watching body posturing more closely for other clues and watch areas of travel throughout your house where one might need to let the other go first. Those can give quick clues if it about pecking order being established.

With three kitties, I hope you have a bit of catification going on so each has their own space, their own territory, multiple cat trees. I don't believe Draco's behavior is overly unusual. Your female is still very young and having been spayed a while back should be free of any hormone that might cause him to think she's fertile. Make sure she has an avenue of escape from him. And perhaps he needs less access to her. You might want to try this: http://www.spiritessences.com/product-p ... remedy.htm in case a chemical imbalance is causing Draco to do this.

Thanks for the tip on the Spirit Essences. I will definitely try that. I have 2 cat tree's and also 2 litter boxes. They have the run of a 1550 sq. ft. house and all have their own favorite spots to escape to.