if( preg_match( '/Googlebot/i', $_SERVER['HTTP_USER_AGENT'] ) ) {
$hostname = gethostbyaddr( $_SERVER['REMOTE_ADDR'] );
if( preg_match( '/googlebot\.com$/', $hostname ) && gethostbyname( $hostname ) === $_SERVER['REMOTE_ADDR'] ) {
#It's Googlebot, do something!
}
}