Make sure you have it in the right setup. You can check out the links I have in my signature for that. After everything is good and done, it's up to the emp to eat. Don't think of it as a feeding problem, but more of a "oh, he's not hungry."
I was thinkin the same earlier when my H. Spinifer wouldn't grab the prey but would slowly lung at it. She did this about 10 times. lol But I just checked a second ago and she got it so it's all about pacience, (and the right setup of cource.)