Creating a wildcard custom attack signature

When creating custom attack signatures to block user-agents that contain various versions of bots or spiders, rather than naming the specific keyword in the rule (such as msnbot), is it possible to make this a wildcard rule to block anything with the word bot in it, for example *bot or *spider? It's difficult to keep up with all of the different versions of bots, spiders, and crawlers hitting our sites. Thanks!