When you 'create' a thread - at the point at which you 'create' - the process state is copied.

That can get quite expensive on memory overhead, yes. That is the way of things if you want to use Perl threads. You can mitigate it a little, by limiting memory footprint of your originator, and 'create' before you start filling memory with stuff you don't need in every thread.

If you're on a system that supports it natively (e.g. most Unixes) then fork() may be an alternative - as most kernels implement copy-on-write for forked processes, meaning that they're very memory efficient. However you lose some of the conveniences that you'd get from e.g. threading.