Zoology A Closer Look: Pepsis Formosa (Tarantula Hawk)

Discussion in 'Zoology' started by drlau, Apr 7, 2005.

  1. drlau

    drlau Premium Member

    ID member overrocked posted a link to Desert Animals & Wildlife in the Zoological Resources thread, and I found this interesting (if somewhat frightening) insect.

    Common name:
    Tarantula Hawk

    Scientific Classification:
    Kingdom Animalia
    Phylum Arthropoda
    Class Insecta
    Order Hymenoptera
    Family Vespidae
    Genus Pepsis
    Species Pepsis formosa


    Several species of the wasps known as "tarantula hawks" inhabit the desert lands of the southwest. Pepsis formosa and Pepsis thisbe are probably the two most common. Wasps in the genus Hemipepsis are also known as "tarantula hawks." The species are difficult to distinguish.

    Description

    Body lengths measures up to two inches, and the wasps are rather robust, which provides good protection during encounters with tarantulas. The insects are metallic blue-black with wings that are blue-black, orangish or mahogany in color. This is another group of insects which, like velvet ants, have aposematic coloring – that is, conspicuous warning coloring – which warns potential predators that this is a meal that might be more painful that it is worth.

    Range

    Pepsis is a New World genus, with species occurring from Argentina northward to Logan, Utah. Over 250 species are found in South America. Fifteen occur in the United States, with at least nine occurring in the deserts. Tarantula hawks occur wherever tarantulas are found. P. thisbe is the most northern ranging of the genus.

    Predator and Prey

    Only a few animals, such as roadrunners, eat tarantula hawks. The wasps are "nectivorous," and they have been known to become "flight-challenged" after consuming fermented fruit. :lol:

    Habits and Habitat

    Tarantula hawks are most active in the summer, during the day, although they avoid the highest temperatures. Females give the wasps their common name. Like all members of this genus, they require a spider to serve as host for their larvae, and in the case of the local species, tarantulas are the preferred nursery.

    A female wasp finds a tarantula by smell. Generally, she scampers across the ground to locate a burrow. She will enter the burrow and expel the spider, then attack it. She may also encounter a male tarantula during his search for a mate. In an attack, the wasp uses her antennae to probe the spider, which may raise its front legs and bare its fangs. (A tarantula does not always counterattack.) She then attempts to sting the spider. She might seize the spider by a leg, flip it over on its back and sting it, or she may approach from the side to deliver a sting. Once stung, the tarantula becomes paralyzed within seconds. The condition will last for the remainder of its life. The wasp may drink the body fluids oozing from the spider’s wounds or from its mouth to replenish nutrients and water she used during the attack.

    If the wasp expelled her victim, she will drag it back into its own burrow, now a burial vault, lay a single egg on the spider’s abdomen, then seal the chamber. If the wasp succeeds in stinging a male tarantula on a mating hunt, she will excavate a burrow, drag the paralyzed spider inside, lay her single egg, and seal the chamber.

    Once the egg hatches, the tiny grub, initially connected to the spider by the tip of its tail, bends over, attaches its head and begins to suck. It continues sucking until its final moult. It then rips open the spider's abdomen, thrusts its head and part of the thorax inside, and "feeds ravenously," as one entomologist described it. As one might hope, even for a spider, the tarantula at this point is finally dead.

    Male tarantula wasps also lead an intriguing life. They engage in a behavior called "hill-topping," where they perch on taller vegetation or high points. They are strongly territorial at these sites because of the good view of the surroundings and in particular, of newly emerged virgin females, which may be receptive to mating. Once again we see that males of another species act quite like males of our own species; think of males posted up at a bar keeping an eye on the door.

    Notes

    Tarantula hawk stings are considered to be the most painful of any North American insect. Christopher Starr wrote an article entitled, "A Pain Scale for Bee, Wasp and Ant Stings." On a scale of one to four, Pepsis formosa was one of only two insects to rate a four. This compares with a one for a Solenopsis xyloni (desert fire ant), two for a Apis mellifera (honey bee) and three for a Dasymutilla klugii (velvet ant).

    One researcher described the tarantula hawk’s sting this way: "To me, the pain is like an electric wand that hits you, inducing an immediate, excruciating pain that simply shuts down one’s ability to do anything, except, perhaps, scream. Mental discipline simply does not work in these situations. The pain for me lasted only about three minutes, during which time the sting area was insensitive to touch, i.e., a pencil point poked near the sting resulted only in a dull deep pressure pain."

    Tarantula wasps are unusual in the severity of their stings. Generally, it is the more social insects that deliver the most painful stings because they have a large nest to defend. Researchers hypothesize that the Pepsis as well as the Dasymutilla have evolved such painful stings because they spend so much time out in the open, exposed to potential predators.

    Although painful, the Pepsis sting is not especially lethal. It rates a 38 on a lethal capacity scale. This compares with 5.9 for a Dasymutilla klugii, 54 for a Apis mellifera, and 200 for a Pogonomyrmex maricopa (a desert-dwelling seed-harvester ant).