Facing death together: heterospecific aggregations of blowfly larvae evince mutual benefits

Heterospecific aggregations and foraging associations have been observed between different species, from apes to birds to insects. Such associations are hypothesized to result in a mutually beneficial relationship entailing benefits that are not apparent in conspecific groupings. Therefore, the objectives of the present study were to investigate 1) how 3 blowfly species, namely, Calliphora vicina, Calliphora vomitoria, and Lucilia sericata, aggregate according to species, and 2) if developmental benefits are linked to heterospecific aggregation. For objective (1), larvae of 2 species were placed between 2 conspecific aggregates, each with a different species (i.e., a binary choice test). After 20 h, the positions of all larvae were determined. On average, 98% of the maggots added later settled together on one of the 2 pre-existing aggregations, demonstrating a collective choice. The aggregation spot with C. vicina was preferred against others, indicating different attractiveness of different species. To relate this behavior to its benefits (objective ii), C. vicina and L. sericata larvae were raised from first instar to adult in con- and heterospecific conditions, and their development time, mortality rates, and morphometrics were measured. Thereby, mutual and asymmetric consequences were observed: specifically, there were significant increases in size and survival for L. sericata and faster development for C. vicina in heterospecific groups. These results indicate that the predilection for heterospecific association leads to mutual developmental benefits. This heterospecific aggregation behavior may be a resource-management strategy of blowflies to face carrion-based selection pressure. This study highlights how heterospecific associations of blowflies improve their development, a likely strategy to face harsh environmental conditions. The coexistence of competing species has been observed between different animals, from apes to birds to insects. Using blowfly larvae, we have shown the existence and benefits of heterospecific aggregations within Diptera. These benefits in development time, survival, and size were apparent within heterospecifics but not in conspecific groups.