These worms appear soon after the rain lilies flower and slowly nibble on the leaves growing big and chubby. They are about 5cm long, have many small red legs underneath, have no spines or spikes, and are soft-bodied. They leave tiny green balls of excreta. I have never seen them metamorphose. I live in Andhra Pradesh in India. Can anyone tell what species they are? Are they dangerous?
I think you have an Indian Lily Moth (of the genus Polytela). It is considered a minor pest. Their habitat seems to only be around India and its surrounding area.
Their worm matches yours ... smooth, dark, but red patches and white spots:
If you dig in your garden, you may encounter these pupae:
And they eventually grow into these beautifully-multicoloured moths:
Here is a video showing their movements and their life cycle: