Comparative nesting biology of two species of Australian lithocolous ants: Polyrhachis (Hedomyrma) turneri Forel and P. (Hagiomyrma) thusnelda Forel (Hymenoptera: Formicidae: Formicinae)

Abstract

Abstract The nests of both Polyrhachis (Hagiomyrma) thusnelda and P. (Hedomyrma) turneri are restricted to the sides of rock walls (lithocoly), but, despite the similar nesting localities, the nests differ in the types of construction material used. The walls of nests of P. thusnelda are constructed of carton material without any silk, while those of P. turneri are comprised of a thick and diffuse mass of fluffy silk with very little carton. However, unlike other species of Polyrhachis that live in silk nests, the silk material in nests of P. turneri is produced entirely by spiders and not their own larvae. Scanning electron microscopy indicated that the silk strands found in natural P. turneri nests resembled those of nearby spider egg sacs rather than the strands found in the cocoons of their own larvae, and captive brood‐right colonies of P. turneri failed to produce silk nests in the absence of an external silk source. These results: confirm the existence of an additional nesting habit within the genus, lithocoly; suggest there are at least two ways by which lithocolous nesting habits can evolve, carton vs. silk; and indicate that the presence of silk within a nest need not imply that ant larvae are the source. Studies of the distribution and evolution of nest‐weaving within the genus Polyrhachis may need to be reassessed, now that the presence of silk nests could actually represent the origin of two independent behavioural traits (silk from larvae vs. silk from external sources such as spiders).