Critter Corner
The Preservation News. October, 2000
© 2000

by Lenny Vincent

Tarantula Hawk Wasp.

When I see Pepsis cruising over the coastal sage, I think of helicopter gunships: slow, formidable and lethal. Pepsis is the genus of wasp to which tarantula hawks belong. I have seen Pepsis as large as two inches long with wingspans of four inches. Their bodies are steel blue to black in color and the wings are orange. The stinger (only females have them) is about a quarter inch long and, when the wasp is provoked, delivers the most painful sting of all local insects.

In spite of its threatening appearance and painful potential, the adult wasp is a vegetarian. Both males and females use their relatively short tongues to sip nectar from flowers with shallow corollas. It is the immature wasp (the larva or grub) that, is a carnivore, and feeds on a tarantula.

Adult females fly slowly over our coastal sage seeking tarantula burrows. When a burrow is spotted the wasp flies to the entrance where she gently palpates the ground to lure the tarantula out. The tarantula lunges out expecting prey only to find its mortal enemy. The poorly sighted tarantula hardly has a chance. Its tactile sensory systems seem to fail the spider and its behavior often seems strangely passive considering the circumstances. Even if the tarantula does try to vigorously defend itself with its huge fangs and weight advantage, it rarely wins the contest. The tarantula hawk bends its long abdomen forward and underneath the tarantula to deliver a paralytic venom with its mighty stinger.

Once stung, the spider soon becomes motionless. Its metabolic rate almost ceases. The seemingly lifeless spider is dragged backwards over the ground to the wasp's burrow. Periodically the wasp loosens its mandibular grip on the spider's leg to fly about and check the terrain. It then resumes its backward task. One entomologist witnessed a tarantula hawk dragging a spider over a hundred yards.

The tarantula hawk lays a single whitish sausage-shaped egg on the spider's abdomen once the spider is safely tucked away in a burrow. If the tarantula is relatively small, the wasp will lay an unfertilized egg which will produce a male wasp. Adult males are smaller than adult females. If the tarantula is relatively large, a fertilized egg will be laid. Fertilized eggs develop into females.

The egg soon hatches into a grub that now has fresh spider meat to consume. The spider, still paralyzed, remains alive during much of this consumption because the larva saves the vital organs for last. In time the larva will eat the entire tarantula except for its exoskeleton. The larva then pupates. This is its transitional stage. Soon an adult wasp will emerge from the pupal case, dig its way out of the burrow, and start the process over.

Adult female wasps may provision several burrows, each with a single spider for the single egg that is laid within. Tarantulas need not fear extinction due to this wasp. A successful female tarantula may produce, over her many years, several eggs sacs of 200-400 eggs.

Lenny Vincent teaches biology at Fullerton College and is on the Board of Directors of the Laguna Greenbelt, Inc.