Nice stuff so far. You seem to have good control over your variation in tones, and the insect studies are excellent!
I think you could really benefit from investigating anatomy rigorously. Check up on some books recommended from time to time here, there are quite a few; make sure you pick one that's suitable to what you want, though.
And unless it's a conscious decision, don't be too timid. These are just sketches, try to work aggressively and really understand what you're looking at or thinking about.
"If something looks too big, make it bigger. If it looks too small, make it smaller. You're dealing with fear here, not right or wrong."