Abstract
During mating season, males of synchronous firefly species flash in unison within swarms of thousands of individuals. These strongly correlated collective displays have inspired numerous mathematical models to explain how global synchronous patterns emerge from local interactions. Yet, experimental data to validate these models remain sparse. To address this gap, we develop a method for three-dimensional tracking of firefly flashes, using a stereoscopic set-up of 360-degree cameras. We apply this method to record flashing displays of the North American synchronous species Photinus carolinus in its natural habitat as well as within controlled environments, and obtain the three-dimensional reconstruction of flash occurrences in the swarm. Our results show that even a small number of interacting males synchronize their flashes; however, periodic flash bursts only occur in groups larger than 15 males. Moreover, flash occurrences are correlated over several metres, indicating long-range interactions. While this suggests emergent collective behaviour and cooperation, we identify distinct individual trajectories that hint at additional competitive mechanisms. These reveal possible behavioural differentiation with early flashers being more mobile and flashing longer than late followers. Our experimental technique is inexpensive and easily implemented. It is extensible to tracking light communication in various firefly species and flight trajectories in other insect swarms.
Highlights
Flashes are more than a mere midsummer night’s wonder: they express a sophisticated social behaviour characterized by male courtship and female mate choice [1]
We provide with this paper a standalone FireflyNavigator software tool for the reader to interactively navigate reconstructed firefly swarms and visualize trajectories
The three-dimensional reconstruction of flash occurrences in the natural habitat (5 min interval starting at 22.00) shows a P. carolinus swarm that closely follows the slope of the surrounding terrain, and notably flashes almost exclusively in a layer of about 2 m above ground
Summary
Flashes are more than a mere midsummer night’s wonder: they express a sophisticated social behaviour characterized by male courtship and female mate choice [1]. Swarms are mass-mating events that contain purposeful internal dynamics [2]. Fireflies offer a rare glimpse into insect communication, as their broadcasting signals, consisting of intermittent and periodic flash patterns, are readily traceable even in congested groups. It is possible to separate movement from communication, unlike in other insect swarms where trajectories are a proxy for social interactions [3,4]. Male fireflies advertise themselves to stationary females on the ground by flashing their species-specific patterns to be identified as potential mates [2,5]. Flash production is a voluntary action, resulting from the well-timed release of the neurotransmitter octopamine triggering the luciferin–luciferase chemical reaction in the insect’s lantern [6]
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