Oooh, I know how to make it darker! I just learned this not too long ago. Click on the arrow next to the render ball. The Auto gamma correction is checked by default. If you uncheck it, it makes a big difference. That's all you might have to do to make it darker. Of course if you have already done this then I feel stupid. :P Anyway, I do agree that it should be darker, too. And if that green thing is grass, I would make into spider blood. Just my 2 cents. :) I still think it's a great image! Can't wait to see the end product. :)

~Damia~ LeviathanPhotography