I saw three of these large hummingbird-like moths near dusk. They were feasting on the pollen from my Pentas flowers. At first I thought they were baby hummingbirds, their wings were beating like a hummingbird, but there was no noise that could be heard from the wing beats. They had a 3-4 inch wingspan and a slightly shorted body length. I haven't got a clue what they are, but they are large and very unusual. The wings looked somewhat moth-like, but the wing flap rate was very fast, faster than any moth I have seen before. Can anyone help me to identify this Insect?