Eurypelma californica, common in several southwestern [U. S. A.] states, has been under observation for about 9 yrs., with the result that the life cycle and the mating habits of the [male] are fairly definitely known. The life cycle from hatching till sexual maturity is about 11 years, with the possible variation of 1 yr. more or less. During this time, a [male] undergoes about 22 molts. Until the last molt the [male] is indistinguishable from the 9. As many as 4 sperm webs are made by 1 [male], indicating that he will mate at least 4 times. In preparation for mating the stimulation of the sex glands is surprisingly thorough and deliberate for so low a form of animal life. Mating has been observed 10-12 times. After the mating season the [male] decline in vigor, and die apparently from total exhaustion of all sources of energy. The [female], judging by records not quite complete, become mature when 12 or 13 yrs. old. After attaining maturity, they live for perhaps 20 yrs. and probably much longer.