No doubt large numbers are devoured by insectivorous birds, mammals and reptiles, but the mortality due to them and other foes sinks into insignificance beside that caused by the persecution of hymenopterous insects of the families Ichneumonidae and Pompilidae, especially of the latter, many species of which systematically ransack the country for spiders wherewith to feed their young in the breeding season.
Now the Pompilidae or mason wasps provision their cells with insects of many different kinds, as well as with spiders; but, of the hundreds of species of these wasps that have been described from different parts of the world, only one is known to use ants for this purpose; and this species is not one that preys upon spiders.
Since the adoption of an aquatic mode of life by Desis and Argyroneta involves no increased facilities in getting food, and merely substitutes for ordinary terrestrial enemies fishes and crustaceans in the former case, and fishes, amphibians, and insectivorous water-insects in the latter, the supposition is justified that the change in environment is due to the unremitting persecution of Pompilidae and Ichneumonidae, which would not venture to pursue their prey beneath the water's surface.
Nevertheless, as explained below, it seems to be highly probable that ant-imitating insects and spiders, when the resemblance is dependent to a greater extent upon size, shape and movement than upon tint, have acquired their mimetic likeness especially to protect them from the attacks of such insect-enemies as predaceous wasps of the family Pompilidae, flies of the family Asilidae, and from socalled parasitic hymenoptera of the family Ichneumonidae, as well as from other insect-eating Arthropods.
In Mashonaland, for instance, a large number of genera and species of Hymenoptera belonging to the Apidae, Eumenidae, Sphegidae, Pompilidae, Scoliidae, Tiphiidae and Mutillidae, resemble each other in having black bodies and dark blue wings.