It happened last year and this was happening now. I was wondering. My lovely little Kalanchoe blosfeldiana plant was suddenly becoming ugly and leaves changing colour. I had guessed it was overwatering or some behaviour of the plant itself. It had grown back. This time, I took the pot [ small one] up in my hand and took a close look. There was something in the leaves!!
The fleshy green leaves were becoming transparent. When I held the plant leaves to the sun, I could see that and the tiny poops revealed it:
There were larvae inside, eating the chlorophyll, going inside... I had seen the leaves being cut and eaten, with holes, but not something like this! They were happily feeding on the leaves, hiding from predators. I guessed they would be of a grass blue butterfly and today, I checked they were indeed, the larvae of Pale Grass Blues which are common in my yard. I had seen two pairs mate in the last one week.
The leaves would grow back slowly, but in the fear, I removed them. Next time, I'll leave them alone.