I kinda feel like this was written for beginners, but if its not that, I can't say this was really well researched. There are a ton of more technical things that you can do to defend yourself, and any expert will tell you that pretty quickly.
Also, if a search engine crawling you is a "high volume of traffic" to your site, you are doing it wrong. Search engines are designed to be pretty lightweight in terms of crawl load, but occasionally can get broken with bad CGI/apps/etc, but never to the point that they would appear to be part of a DDoS.
Also, if a search engine crawling you is a "high volume of traffic" to your site, you are doing it wrong. Search engines are designed to be pretty lightweight in terms of crawl load, but occasionally can get broken with bad CGI/apps/etc, but never to the point that they would appear to be part of a DDoS.