If the explosion of Halloween merchandise in stores isn't horrifying enough, late summer also marks the incursion of a tiny beast: the tarantula hawk. The tarantula hawk is a large (up to 2.5 inch) wasp that parasitizes tarantulas. The female wasp delivers a sting to its prey, which paralyzes but does not kill the tarantula. She then drags it off to her burrow and lays an egg in its abdomen. When the egg hatches, the larva begins feeding on the non-vital organs of its still-living host. I recall several X-Files episodes that were almost this gruesome.
Tarantula hawks are found throughout the world, everywhere except Europe and Antarctica. Here in our South County chaparral, we are most likely to encounter one of two species: Pepsis thisbe or Pepsis grossa. They have distinctive metallic blue-black bodies and orange wings. Males have straight antennae while females antennae are curly. Only the females sting.
Unless you're a spider, tarantula hawks are quite docile and do not sting humans unprovoked. Most of the reported stings have been to over-enthusiastic collectors. The sting is said to be one of the most painful in nature. Justin O. Schmidt author of The Sting of the Wild: The Story of the Man Who Got Stung for Science states: "Stung by a tarantula hawk? The advice I give in speaking engagements is to lie down and scream. The pain is so debilitating and excruciating that the victim is at risk of further injury by tripping in a hole or over an object in the path and then falling onto a cactus or into a barbed-wire fence."
Because of their nasty sting, few animals will risk a meal. The roadrunner is a rare exception. The roadrunner catches the wasp and quickly bashes it against the ground or rocks to crush the exoskeleton. This kills the insect and neutralizes the stinger, softening it for a tasty, high-protein meal.
Contrary to their grisly reputation, tarantula hawks do not decimate the tarantula population, but rather, are part of the ecological balance. Each female wasp will provision 4-6 larvae in her lifetime, a modest control of tarantula numbers. As an added bonus, adults feed on nectar from soapberry and milkweed flowers, providing pollination to these native species.
Like many members of the Hymenoptera (ants, bees, and wasps), female tarantula hawks can determine the sex of their offspring. Storing sperm in an organ called a spermatheca, they can choose whether to release sperm when an egg is laid. Females are produced from fertilized eggs, and males are produced from unfertilized eggs. Since females do the lion's share of hard work—tackling a tarantula and dragging it into their burrow—nature favors female numbers.
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