The cactus is cool. I see what James is talking about.
The latest shrimp flower shot is very good, but the lighting is direct and hot.
The Spider is Awesome! I like that a lot. Great composition and exposure. The color is great as is the sharpness. Clipping off the tips of his hind feet is a little distracting, but only slightly. And of course with the same lighting, the flash is a little harsh.
The lizard is great, composition is your main issue there. Look at how sharp that eye is:)
And that spider is very cool!. Composition, exposure and sharpness all great. But again the flash is hot.

For flash work like this here is what I use, a Lumiquest bounce card. It looks though like you are using maybe the onboard flash, and that will give you the direct hash lighting. If you get an external flash and remove it from the camera and bounce the light, you will be very impressed. You are making some great progress.