Very nice stuff. I started with upgrading juice and bigger webs while setting in the center, but then I ran out of juice and could not catch any thing with my low speed. Next attempt I camped one corner and quickly realised why you said ".. it won't last for long!" :) . So the final attempt went ahead and upgraded both movement speed and more flies while alternating between both the top right and the bottom left corner. Turns out this was the ultimate strategy since. At the end the health was deplating way faster than I could run from one corner to the other so I eventually after surviving till 700.
Simple game yet very appealing.