$crawlers = array(
        'Googlebot',
        'Baiduspider',
        'ia_archiver',
        'R6_FeedFetcher',
        'NetcraftSurveyAgent',
        'Sogou web spider',
        'bingbot',
        'Yahoo! Slurp',
        'facebookexternalhit',
        'PrintfulBot',
        'msnbot',
        'Twitterbot',
        'UnwindFetchor',
        'urlresolver',
        'Butterfly',
        'TweetmemeBot'
    );
$implCrawlers = implode('|', $crawlers);
$isBot = (strpos($_SERVER['HTTP_USER_AGENT'], $implCrawlers ) !== false) ? true : false;
if (!$isBot) {
...
}