Firstly, I like this batch of shots. I'm going to offer a fair bit of critique here, but I'm not trying to be down on your images, just trying to present some different creative options or things to play around with... Hopefully that's ok!
For starters the green leaf behind the spider in #1 is a bit of a distraction (for me), not so much that it's in the image but that it cuts through the subject. But otherwise the "poses" and compositions are quite nice. On a creative option note: Maybe a slightly more open aperture could creater softer backgrounds? Especially as you seem to have plenty of DOF for the subject, it could be something to try playing around with just for some different effects...
I will also "+1" Scott's (Busiboy) comments on the flash being a bit "hot". Out of curiousity - What's different with the design of your flash compared to the conventional Nikon/Canon hot-shoe mount flash units?
If it all possible, it's really worthwhile trying to adapt even a small diffuser onto the flash for a few of reasons:
1) (While not always desirable) You can create a softer light on the subjects with less contrast, which can actually help reveal some of the finer details in darker areas in some
2) Light fall off. (If I remember the theory correctly) With a diffuser in use, the light will fall away (loose intensity) more quickly over the same distance when compared to the light fall off from a bare flash. The means near-distance background objects are less brightly lit helping to seperate the subject out from the background.
3) Easier to blend with natural light if you choose to mix in that to your shots.
4) Creates a broader area to reflect. With the third shot you've posted in this thread for example, more of the web would be visible, due to having a larger lightsource lighting it, as the broader area of the diffuser helps "wrap" the light around the subject. In this shot it'd possibly also help to light the outer extremities of the spider too.
Again, just little things to toy with if you can make it work for your flash. Even a home-made one made out of cereal-box cardboard, sticky-tape and some tracking paper will be enough just to trial some of the different techniques or "feels" available with a diffuser. It doesn't have to be pretty after all - It's not in the picture!
While the longer focal length macros are handy for creating tighter focus/compositions of the subject and "flattening" perspectives, the 50mm/55mm macros are great for adding in a little extra context to the scene, or playing with the apparent scale of near and far objects thanks to being a bit of a wider angle. And they certainly look to be sharp judging from these examples!