Open the spider_eyes.png and enderman_eyes.png with Paint.NET and save them. It's caused by a change to the transparency engine on those files, and some programs don't give the required format. Paint.NET does.
I don't think it's actually a bug. There's probably a reason for it. Perhaps it's to save on CPU? Not having to read full transparency for those textures would save a lot. If Axel is right, the problem is probably because of the way Photoshop and other programs default to a white background, where some may default to a black background. There are far more serious bugs in 1.8 that need fixing. For example, torches placed underwater allow you to have infinite underwater lightsources, since when they break, the light remains in place.
Thanks for the fast replies everyone but it seems that the patcher was the root of the problem and that I was actually playing on 1.8 pre release still. The problem is fixed now. At least for the regular spiders as I could not find a cave spider.
That makes sense. Thanks again for the help.