Wasps of the genus Sphex (commonly known as digger wasps) are cosmopolitanpredators that sting and paralyze prey insects. Sphex is one of many genera in the old digger wasp family Sphecidae (sensu lato), though most apart from the Sphecinae have now been moved to the family Crabronidae.[1] There are over 130 known Sphex species.
Behaviour
In preparation for egg laying, they construct a protected "nest" (some species dig nests in the ground, while others use pre-existing holes) and then stock it with captured insects. Typically, the prey are left alive, but paralyzed by wasp toxins. The wasps lay their eggs in the provisioned nest and the wasp larvae feed on the paralyzed insects as they develop.
The great golden digger wasp (Sphex ichneumoneus) is found in North America. The developing wasps spend the winter in their nest. When the new generation of adults emerge, they contain the genetically programmed behaviors required to carry out another season of nest building. During the summer, a female might build as many as six nests, each with several compartments for her eggs. The building and provisioning of the nests takes place in a stereotypical, step-by-step fashion.
Sphex has been shown, as in some Jean-Henri Fabre studies,[2] not to count how many crickets it collects for its nest. Although the wasp instinctively searches for four crickets, it cannot take into account a lost cricket, whether the cricket has been lost to ants or flies or simply been misplaced. Sphex drags its cricket prey towards its burrow by the antennae; if the antennae of the cricket are cut off, the wasp would not think to continue to pull its prey by a leg.
Some Sphex wasps drop a paralyzed insect near the opening of the nest. Before taking provisions into the nest, the Sphex first inspects the nest, leaving the prey outside. During the inspection, an experimenter can move the prey a few inches away from the opening. When the Sphex emerges from the nest ready to drag in the prey, it finds the prey missing. The Sphex quickly locates the moved prey, but now its behavioral "program" has been reset. After dragging the prey back to the opening of the nest, once again the Sphex is compelled to inspect the nest, so the prey is again dropped and left outside during another stereotypical inspection of the nest. This iteration can be repeated several times without the Sphex changing its sequence; by some accounts, endlessly. Dennett's argument quotes an account of Sphex behavior from Dean Wooldridge's Machinery of the Brain (1963).[6]Douglas Hofstadter[7] and Daniel Dennett[8] have used this mechanistic behavior as an example of how seemingly thoughtful behavior can actually be quite mindless, the opposite of free will (or, as Dennett described it, sphexishness).
Philosopher Fred Keijzer challenges this use of Sphex, citing experiments in which behavioral adaptations are observed after many iterations. Keijzer sees the persistence of the Sphex example in cognitive theory as an indication of its rhetorical usefulness, not its factual accuracy.[9] Keijzer also noted that repeated inspection of a disturbed nest may very well be an adaptive behavior, thus diminishing the aptness of Hofstadter's metaphor.[9]
