What an absolutely horrible standard to set for your students. Talk about an awful role model. I agree with the other posters here that said to mention the "encouraging irresponsible practices" angle. If they have a teacher that is endorsing poor animal care practices by neglecting his animals, using them as ornaments for his classroom without any thought to their needs or wellbeing and then JUSTIFYING IT when a concerned student REPEATEDLY inquires about the health of his animals, it needs to be addressed, and I feel that any school administrator would be deeply troubled if they had this case brought to them. Especially in regards to possible animal abuse, no school wants issues with law enforcement. Bring up that they're lacking basic necessities like heat sources (absolutely needed for cold blooded creatures) and places to hide for security, and the fact that he doesn't feed them. I would also try to recall how many times you talked to him and on what days, to give them a timeline. Also let them know that you've been taking time out of your day and money out of your bank account to care for this mans animals. You're a good person for being so adamant about the situation, I wish you luck and I hope something gets done for those critters before school is out.
ps the fact that this dude is a bio teacher kills me. absolutely ridiculous.