The Insectarium is a little facitily located on Canal Street in the US Customs Building. I think admission is now up to over $15 so I'd suggest the better value of $44 for the Aquarium, Insectarium, and Zoo combined, you at least save a couple dollars.
They have several stations set up with employees to tell you about specific bugs and allow you to touch them if you want, so that's informative - don't be afraid to ask questions! The butterfly exhibit is nice if you haven't been to the one in Key West (which is unbelievably amazing)...I also think it depends on how many butterflies they're able to keep at once. The lifespan of a butterfly is about two weeks so I imagine the population in there fluctuates a lot..there just weren't many when we went this weekend.
There's a fun little movie, too.
It's definitely worth it to go if you go ahead and get it with the zoo and aquarium package.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.