Tool Use in Digger Wasps (Hymenoptera: Sphecinae)

"Tool-use" by a digger wasp was first described by Williston (1892) and Peckham and Peckham (1898). They observed this remarkable behavior in two species of ground-nesting wasps, Ammophila urnaria and Ammophila aberti. The female digs a burrow in the ground, provisions it with paralyzed caterpillars, lays an egg on top of the food cache and then fills the burrow with soil or stones. While closing the nest, the wasp picks up a pebble in her mandibles and pounds the substrate with it, thereby compacting and settling the soil that was used to fill the nest. The Peckhams said that in this behavior, the wasp had "...improvised a tool and made intelligent use of it." The behavior received much publicity (see Frisch, 1940; Lamburn, 1955; Evans, 1959) and several authors saw tool using as evidence that wasps have highly plastic, intellectual powers (Rau and Rau, 1918; McDougall, 1923; Bouvier, 1922). Others have interpreted the behavior differently. Rather than thinking of tool using as insightful, they described the behavior as a species-typical, instinctive act (Holmes, 1911; Frisch, 1940; Baerends, 1941; Evans, 1959) or possibly an example of trial-and-error learning (Thorpe, 1956). Although some have questioned whether the behavior should be considered true tool use (Frisch, 1940; Evans, 1959), the action clearly falls under the current definition (Alcock, 1972; Wilson, 1975). When Ammophila uses a pebble as a hammer, she is manipulating an object, not internally manufactured, with the effect of improving her efficiency in altering the position, form or condition of some other object in the environment (Beck, 1980; Alcock, 1972). How did such extraordinary behavior evolve? The Sphcida are a large family of solitary (usually), hunting wasps. In general, the female constructs a nest which she provisions with one to several paralyzed arthropod prey as food for the single