Social insects and beyond: The physics of soft, dense invertebrate aggregations

Abstract

Aggregation is a common behavior by which groups of organisms arrange into cohesive groups. Whether suspended in the air (like honey bee clusters), built on the ground (such as army ant bridges), or immersed in water (such as sludge worm blobs), these collectives serve a multitude of biological functions, from protection against predation to the ability to maintain a relatively desirable local environment despite a variable ambient environment. In this review, we survey dense aggregations of a variety of insects, other arthropods, and worms from a soft matter standpoint. An aggregation can be orders of magnitude larger than its individual organisms, consisting of tens to hundreds of thousands of individuals, and yet functions as a coherent entity. Understanding how aggregating organisms coordinate with one another to form a superorganism requires an interdisciplinary approach. We discuss how considering the physics of an aggregation can yield additional insights to those gained from ecological and physiological considerations, given that the aggregating individuals exchange information, energy, and matter continually with the environment and one another. While the connection between animal aggregations and the physics of non-living materials has been proposed since the early 1900s, the recent advent of physics of behavior studies provides new insights into social interactions governed by physical principles. Current efforts focus on eusocial insects; however, we show that these may just be the tip of an iceberg of superorganisms that take advantage of physical interactions and simple behavioral rules to adapt to changing environments. By bringing attention to a wide range of invertebrate aggregations, we wish to inspire a new generation of scientists to explore collective dynamics and bring a deeper understanding of the physics of dense living aggregations.

No neonates without adults

“…(1) borrow concepts from established programs that mass-rear sterile fruit flies, screwworms, and mosquitoes; (2) conduct studies that can link knowledge across disciplines (e.g., [121][122][123] ); and especially, (3) pursue fieldwork that assesses the wild flies, their ecology, genetic diversity, and associated microbiota.…”

“…As was the case for larvae a decade ago, information surrounding adult H. illucens is fragmentary and presently must be scaffolded by that gleaned from other study systems. To address this, future work might: (1) borrow concepts from established programs that mass‐rear sterile fruit flies, screwworms, and mosquitoes; (2) conduct studies that can link knowledge across disciplines (e.g., [ 121–123 ] ); and especially, (3) pursue fieldwork that assesses the wild flies, their ecology, genetic diversity, and associated microbiota.…”

Active many-particle systems and the emergent behavior of dense ant collectives

“…When together at high densities in three-dimensions, the ant collective can be thought of as an active material with well-defined viscoelastic properties. This makes the ants somewhat analogous to other entangled active materials [66], such as clumps of cells [67] and blobs of worms [68], with possible connections to theoretical treatments of active viscoelastic matter [69,70]. Within a certain frequency range, the rheological response of an ant-collective is predominantly elastic, with a mechanical response that is solid-like [58].…”

Collective synchrony of mating signals modulated by ecological cues and social signals in bioluminescent sea fireflies

“…Animal collectives perform some of the most striking examples of behaviour observed [1]. Surprisingly, self-organised aggregations can be the emergent product of individuals following simple behavioural rules [2], as opposed to those that require complicated cognition or decision-making to form.…”