2 days in the past week Google has crawled 10x the average pages crawled per day. What does this mean?

[dellcos]

For the past 3 months my site www.dlawlesshardware.com has had an average of about 400 pages crawled per day by google. We have just over 6,000 indexed pages.

However, twice in the last week, Google crawled an enormous percentage of my site. After averaging 400 pages crawled for the last 3 months, the last 4 days of crawl stats say the following.

2/1 - 4,373 pages crawled

2/2 - 367 pages crawled

2/3 - 4,777 pages crawled

2/4 - 437 pages crawled

What is the deal with these enormous spike in pages crawled per day? Of course, there are also corresponding spikes in kilobytes downloaded per day.

Essentially, Google averages crawling about 6% of my site a day. But twice in the last week, Google decided to crawl just under 80% of my site.

Has this happened to anyone else? Any ideas? I have literally no idea what this means and I haven't found anyone else with the same problem. Only people complaining about massive DROPS in pages crawled per day.

Here is a screenshot from Webmaster Tools: http://imgur.com/kpnQ8EP

The drop in time spent downloading a page corresponded exactly to an improvement in our CSS. So that probably doesn't need to be considered, although I'm up for any theories from anyone about anything.

[dellcos]

2 weeks later, 2 more large spikes of 10X average...nothing bad is happening...oh well...