Use the following in .htaccess:

RewriteEngine on
RewriteCond %{HTTP_USER_AGENT} ^Bullseye.* [OR]
RewriteCond %{HTTP_USER_AGENT} ^fastlwspider* [OR]
RewriteCond %{HTTP_USER_AGENT} ^EmailSiphon [OR]
RewriteCond %{HTTP_USER_AGENT} ^EmailCollector [OR]
RewriteCond %{HTTP_USER_AGENT} ^EmailWolf [OR]
RewriteCond %{HTTP_USER_AGENT} ^ExtractorPro [OR]
RewriteCond %{HTTP_USER_AGENT} ^GetWebPage.* [OR]
RewriteCond %{HTTP_USER_AGENT} ^lwp-tribial.* [OR]
RewriteCond %{HTTP_USER_AGENT} ^Mozilla.*NEWT [OR]
RewriteCond %{HTTP_USER_AGENT} ^Crescent [OR]
RewriteCond %{HTTP_USER_AGENT} ^CherryPicker [OR]
RewriteCond %{HTTP_USER_AGENT} ^[Ww]eb[Bb]andit [OR]
RewriteCond %{HTTP_USER_AGENT} ^WebEMailExtrac.* [OR]
RewriteCond %{HTTP_USER_AGENT} ^NICErsPRO [OR]
RewriteCond %{HTTP_USER_AGENT} ^SurfWalker [OR]
RewriteCond %{HTTP_USER_AGENT} ^Telesoft [OR]
RewriteCond %{HTTP_USER_AGENT} ^Zeus.*Webster [OR]
RewriteCond %{HTTP_USER_AGENT} ^Microsoft.URL [OR]
RewriteCond %{HTTP_USER_AGENT} ^Mozilla/3.Mozilla/2.01 [OR]
RewriteCond %{HTTP_USER_AGENT} ^EmailCollector
RewriteRule ^.*$ - [F]

Note: there may be other harvesters out there that should be added. The Internet is a constantly changing/growing space. 

You might also try using a graphic to show your email address, spelling out the email address as something like me at mydomain.com (rather than me@mydomain.com), or coding the email address in unicode via sites or programs available on the Internet by searching.