Is this a spider bite??? (With pic)

[TamaraDeLempicky]

Do excuse my disgusting leg!!! I woke up a couple of nights ago with an itchy leg. Put some E45 on, forgot about it until yesterday lunchtime when it started itching again. Had a look and found this red mark on my leg. Now today, the mark has got darker and the area down towards my ankle is swollen and hot. Spider? Mosquito?

Not sure, but if the redness expands (draw around the edge of the redness and monitor if it spreads), it tracks (i.e. a red line appears, from the site up your leg) or you feel fluey (shivering/temperature etc.) then you'll need to get it checked out urgently as may have developed into cellulitis and potentially even worse.