Right now it is very similar to a combination of a Husk and Spider, so here are some suggestions:
1. Make it not hostile in the day, but make it follow you around so it can pounce you at night.
2. Make it as fast as the player to make it more dangerous than a normal Spider.
Also, would these spawn in place of Spiders or along with Spiders? Personally I would prefer if there were only Sand Spiders in the desert, to make the Desert a more interesting place.
EDIT: I really like the "creeping out of the sand" thing, though.