No, for security reasons, CloudFlare does not proxy traffic to a wildcard sub-domain. You have to explicitly list the sub-domain as a CNAME in your DNS records to be able to activate CloudFlare.
Can I enable CloudFlare on my root domain (i.e. mywebsite.com) that is an A record?
CloudFlare can only accelerate and protect CNAMEs, not A records, which often includes the root domain. If traffic goes to a root domain and you want to accelerate and protect the traffic using CloudFlare, you can add a redirect to ‘www’.
If you do not forward the traffic, then any traffic to www.mydomain.com will be accelerated and protected by CloudFlare (and shown in the statistics) and any traffic to mydomain.com will not be served by CloudFlare.
If you are using .htaccess to do redirections, here is how you implement a redirect:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^mysite.com$ [NC]
RewriteCond %{SERVER_PORT} ^80$
RewriteRule ^(.*)$ http://www.mysite.com/$1 [R=301,L]`
