I have worms growing on some of my plants, mostly those that are indoors. They eat the leaves voraciously. I've noticed them on spider plants and on the plant whose picture I've attached. Once they get big enough I can grab them with something and throw them out, but sometimes I see that leaves are being eaten and can't find them because they're too small. By the time I find them, they're quite big - about an inch long. Normally I only find one or two at this stage, and they don't move often - only if I shake the branch/leaf they're on or touch them with something.
What are they called? Is there a better way of dealing with them? I've marked them with red ellipses below.