Yeah, I would agree with Mark that your composition and technical skills are probably good enough to have a good shot a stock photography. There is a few things that especially stock photography reviewers are picky about though, that you perhaps haven't had to think about before. These things wouldn't be hard to fix though, and it is just a matter of knowing what they want.
Your landscapes for example, with the lake, are nicely exposed and have a good punch - but I think would be rejected for a very crooked horizon. Very easy to fix!
Some of your insect and nature photography is also quite decent in regards to lighting and composition - however I can see there is significant noise in the image. That is harder to fix and photos allready taken, but I am sure you could figure out how to get fix it on future shots.
So basically I am saying, yeah give it a shot, I think you can definitely be successful at this if you give it a little work. Pick 5 photos for example that you think are the best and submit them and see how it goes. Alternatively first post the 5 photos here and get a quick bit of feedback before sending them in.
And yes, nature can sell quite well on microstock sites. Some of my best sellers are nature shots.