Social Insects and Beyond: The Physics of Soft, Dense Invertebrate Aggregations

TL;DR

This review explores how the physics of soft, dense invertebrate aggregations reveals insights into collective behavior, superorganism formation, and environmental adaptation across various species, emphasizing interdisciplinary approaches and recent physics-based studies.

Contribution

It provides a comprehensive survey of invertebrate aggregations from a soft matter physics perspective, highlighting new insights into collective dynamics and physical interactions.

Findings

Aggregations can include tens to hundreds of thousands of individuals.

Physics of behavior offers new understanding of social interactions.

Invertebrate aggregations function as coherent superorganisms.

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 the physics of the 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.