Sound like a spider bite? Should I go to the ER?

I got bit 2 hours ago, it appeared to me a mosquito bit. It has now turned into a large feverish lump on my thigh above my knee. I have always been ate up by mosquitoes but they have never absorbed into my skin like this. The lump is large enough to cup with you hand and it warm. It's slightly sensitive but not painful. I work in one, but should I go to the ER?