This Hand Gesture Rick Santorum is using, is known as "The Dominant Spider". It tends to be used by primarily by alpha males and somewhat less frequently by alpha females. Although not as dominant or negatively received as the closed-palm or nearly closed-palm down gesture (see Secret # 222: Palms Down vs. Palms Up), it should be used sparingly and for very brief moments in order to assert authority and dominance. If over-used (which doesn't take much and is a strong tendency for the alpha-personality types to do), the audience (even an audience of one) will feel domineered and patronized.
Tonight the former U.S. Senator from Pennsylvania is certainly feeling very dominant - so spiders abound. As of this writing, he is projected to win both the Minnesota Caucuses and the Missouri Republican Presidential Primary. It's still too early to call Colorado's Caucuses, but Rick may have just pull off the hat trick.