Over the past few decades here, I have seen the occasional "40 leg". They are becoming less common. But I have been bit twice. Apparently I dont react to the bite. They arent that fast, I have killed everyone I have seen over the years. I was told to do this by my early Jamaican friends after moving here because they tend to live/hide in dark, damp places that little kids like to explore. The bite can be harmful to a child.
In populated areas, such as Negril, MoBay and Kingston, encountering a 40 leg is becoming more rare. Birds, mongoose and even lizards eat them and keep their populations down. Out in the country, hiding under rocks, rotting trees and other dark, damp areas you can find them more commonly if you are looking.
A home remedy for a bite is a concoction made with a dead 40 leg in an old rum bottle filled with, you guessed it, white overproof rum! Rub the rum on the bite and it acts as an anti-venom.
If you have seen Doctor No, the first James Bond film, when James was whacking that harmless non-Jamaican tarantula (which was walking on a piece of glass above Sean Connery in the scene) - that is the perfect way to kill a 40 leg. You smash it with a shoe as hard and often as you want, to the point of overkill... (pun intended).
They really are an incredible centipede, with their ancestors being on this planet for around 400 million years. But if you do happen to see one, as Captain said above, dont mess with it unless you are going to imitate James Bond.