msnbot was retired from active web crawling in 2010 and replaced with
bingbot - is that what you meant?
Regardless, as covered here, factors that can affect its crawl rate are:
- The total number of pages on a site (is the site small, large, or
- The size of the content (PDFs and Microsoft Office files are typically much larger than regular HTML files)
- The freshness of the content (how often is content added/removed/changed?)
- The number of allowed concurrent connections (a function of the web server infrastructure)
- The bandwidth of the site (a function of the host’s service provider; the lower the
bandwidth, the lower the server’s capacity to serve page requests)
- How highly does the site rank (content judged as not relevant won’t be crawled as often as highly relevant content)
Taking the above into account might help explain the spikes in your requests per minute.
To slow down the crawl rate, specify in your site's robots.txt:
bingbot if you determine that's the bot/user-agent causing the spike. And use a
crawl-delay of 5 (very slow) or 10 (extremely slow) if your server's performance is suffering.