// app/AppKernel.php
class AppKernel extends Kernel
{
    public function registerBundles()
    {
        $bundles = array(
            // ...
            new Nmure\CrawlerDetectBundle\CrawlerDetectBundle(),
            // ...
        );
    }
}

public function indexAction()
{
    if ($this->get('crawler_detect')->isCrawler()) {
        // this request is from a crawler :)
    }

    // you can also specify an user agent if you don't want
    // to use the one of the master request or if the app
    // is accessed by the CLI :
    $ua = 'Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)';
    if ($this->get('crawler_detect')->isCrawler($ua)) {
        // this user agent belongs to a crawler :)
    }
}