Sexual cannibalism is common among orb-web spiders and may limit male copulation frequency. Each copulation by male St Andrew's Cross spiders (Argiope keyserlingi) involves the transfer of sperm from one pedipalp only. Almost half of the males survive their first copulation, but all of the surviving males are cannibalized when they copulate with the other pedipalp. We investigated why males cannot copulate more than twice. Experimentally fatigued males were not cannibalized more frequently than control males. Experimental removal of one pedipalp in virgin males did not increase cannibalism during their first copulation, but the surviving males were unable to copulate with a subsequent female, suggesting they cannot use a pedipalp more than once. Un-manipulated males always inserted their unused pedipalp during their second copulation. Sperm counts from males preserved immediately after copulation and from males maintained for an additional 3 wk show that used pedipalps are not replenished over such a period.