Play Framework 2.4.x plugin to make sure a request pretending to be from a search bot is really coming from that bot.
This filter will not call your controller if the request is malicious, thus reducing unnecessary load. It returns 403 by default, but you may supply your own error handler.
In SBT:
libararyDependencies += "com.osinka.play" %% "play-legitbot" % "2.0.0"
Install the filter in Global.scala:
object Global extends WithFilters(LegitbotFilter)