Why does a female spider wasp lays a egg inside alive tarantula?

noTheir body measures up to two inches. These wasps are tough. They have to be to survive their encounters with tarantulas. The insects are metallic blue-black with wings that are blue-black, orangish or mahogany in color. These wasps have aposematic coloring, which means, it warns its predators. This coloring warns potential predators: 'this is a meal that would be painful, so why risk it?'. Their claws are hooked so can be used against their prey. These wasps are not terribly aggressive, and rarely sting humans, just do not harass them. Their exceptionally potent venom makes these one of the most agonizing insect stings in the world. Though the sting causes excruciating pain, it is not lethal. Most predators find this wasp's venomous stinger, which is 1/3 of an inch long, reason enough to leave them alone. The roadrunner is one of its few real enemies....