Their movement in an upward or downward direction in Limulus and Mygale must exert a pumping action on the blood contained in the dorsal arteries and the ventral veins respectively.
The largest of these is the Mygale with a body 2 in.
A large Mygale found on the island of Siriba, of the Abrolhos group, feeds upon lizards, and has been known to attack and kill young chickens.