Ukrainian glass artist Nikita Drachuk of Glass Symphony creates all manner of glass spiders, octopi, and other critters by hand. He uses a method called lampworking, where a lamp or torch is used to melt rods of colored glass. Once in a molten state, the glass can be formed by blowing and shaping with various tools and small movements. You can see more of their delicate glass critters here.
I do lamp work. This is hard. And they break.