Dumping behaviour of Australian desert ants (Melophorus bagoti) (Hymenoptera:Formicidae)

Abstract

The Central Australian desert ant Melophorus bagoti maintains ground-nesting colonies in the semi-desert habitat. These ants manage waste by dumping items outside the nest. To examine this process, we placed organic and non-organic materials that are associated with either low or high pathogenic risk around or into the nest and observed the nest’s response. We found that generally, ants dumped high-pathogenic-risk materials (dead larvae, dead ants of the colony, foraged food, moth, and non-nest cicada exoskeleton) further from the nest than low-pathogenic-risk ones (sand, buffel grass, cookies), with the exception of (organic) larval shells from their own nest, which were also dumped close to the nest. This pattern of dumping suggests that these ants choose their dumping distance based on how spoilable the experimental materials are.

Desert ants (Melophorus bagoti) learn from experience to improve waste dumping

“…As with our previous study on dumping (Deeti et al 2023a), another unanswered question raised by this study taken together with our work on the behaviour of nest excavators dropping sand outside is: on what basis do the naive dumpers decide to dump an item without rst taking a learning walk? We suspect that chemical cues are at play, but presentation of carefully chosen experimentally treated materials is again surely needed to answer this question of information use, a key question concerning the cognition of ants in executing dumping.…”

“…In a separate study, we observed that even excavators, those workers dropping sand from the nest just outside the nest, do one learning walk resembling the rst learning walk of future foragers before excavating. Sand is dumped within 15 cm of the nest (Deeti et al 2023a), an order of magnitude shorter in distance than the distances at which naive dumpers in this study carried their waste. With more as yet unpublished observations this eld season, we can answer the second question as facultative: we observed a nest in which dumpers took learning walks before engaging in dumping.…”

“…First, experienced ants have learned to navigate well in the area around the nest, or at least in the direction in which they are carrying waste. They can thus execute their dumps by travelling faster and in reasonably straight paths with little scanning, carrying the waste a much longer-and for the nest, safer-distance before dumping the possibly contaminated and pathogenic waste (Deeti et al 2023a). In the distance of dumping, the two groups show no overlap at all in their data (Fig.…”

“…But ants also perform another duty outdoors that requires signi cant travel, that of dumping waste. An earlier study on the dumping behaviour of red honey ants measured the distance at which they disposed of experimentally provided materials (Deeti et al 2023a). Except for ant larva shells, the items of animal origin were dumped at average distances exceeding 5 m. Conversely, items with little or no animal content were dropped at average distances less than 1.2 m (Deeti et al 2023a).…”

“…Besides foraging, some workers dedicate themselves to excavating the nest throughout the day. Nest excavators remove sand from the nest, depositing it within a 10 cm radius outside (Deeti et al 2023a, Deeti et al 2024. A separate study examined the behaviour of naive excavators, while this study focuses on waste dumpers, carrying out the third kind of outdoor task.…”