From my experience most don't as it costs more money (ressources). For me a hidden input with some math solved by Javascript got rid of 10 spam contact requests

From my experience most don't as it costs more money (ressources). For me a hidden input with some math solved by Javascript got rid of 10 spam contact requests per day to actually 0. However of course, the larger a page gets the more dedicated the bots get. But for the plain porn/russian spam it helped.