I was fishing today, rigged up with an unweighted senko. I was casting out and on the drop my rod tip would twitch maybe once or twice or three times and then just stop. Are the fish just biting the tail of the worm or are they just bumping it? What are they doing to it?

Good chance it's bluegills nipping at the worm.  They will hit worms bigger than they are.

That makes a lot sense. They were swarming today.

Ya that happens a lot for me little bluegills and perch go at it, at least it keeps you on your toes!!

I caught about 7 bass on the the back treble of my rattle trap... and had the same problems with t-rigged worms the a curly tail they kept biting my tail off!!

Could be smaller bass, sunnies, perch, etc. Sometimes I've casted to an area numerous times and finally landed the fish I think was nibbling. Its been all the above.

 

Short strikes can be annoying, but are part of the game.

The sunfish wouldn't leave even a 10" worm alone for me on Thursday. It was even worse when I tried a Senko. 

Yup its bluegill for sure. They are a pain in the butt. A few weeks ago I was fishing a 5" worm on a shaky head and got two hits on separate casts. I finally got it on the third try and it was an 8" bluegill.

Could be a bluegill, could be a sunny, could be a bass so all in all it's most likely a fish lol

Bluegill usually give those "machine gun" hits.

^{When this is happening to me, try wacky rigging it if you can without getting snags. It seems to work for me, just having it rigged a different way can make a huge difference.}