Solved my problem. I found that I had written a Perl module that used WWW::Mechanize to pull a piece of information by running the mailing list software; the Perl module exported a function that was called each time a particular HTML web page was viewed (the web page is part of a templating system that enables embedding of functions into the page). The web page isn't in my secured directory so displays of that web page didn't show up in the access log for the secured directory, though the module's use of WWW::Mechanize did. I guess hits on that web page and calls to the Perl module are completed so fast that ps -aux doesn't catch 'em except in a rare coincidence, or maybe they show up in ps -aux merely as an Apache httpd process due to the way the templating system works (Apache::SimpleTemplate).