The moth that Little Bill hatches is a Polyphemus Moth, which is a large North American silk moth. Kiku hatches a Tiger Swallowtail butterfly, and Andrew hatches a Monarch butterfly.
Big Bill: You know, I saw a monster movie once, where a giant monster moth took over the whole city!
This is most likely a reference to Mothra, a giant Japanese monster moth that has been known to wreak havoc (especially when she's a caterpillar.) Mothra has also been known to battle or team up with Godzilla on more than one occasion.