Social stinging insects, such as honey bees and many species of wasps, operate as complex societies where the colony functions much like a single living entity, often called a superorganism. Living in dense, confined spaces provides ideal conditions for pathogens to spread rapidly, posing a constant threat. To combat this inherent risk, these insects have evolved remarkable behavioral and chemical mechanisms to manage disease. The collective health of the colony depends on the ability of its members to detect illness and for sick individuals to remove themselves from the nest. This strategy ensures the survival of the group, demonstrating how social behavior is shaped by the pressure of infectious disease.
How Stinging Insects Detect Illness
The first line of defense is recognizing an infection, which often happens through subtle chemical changes. Sick insects frequently exhibit an altered chemical signature on their bodies, primarily affecting the cuticular hydrocarbons that coat their exoskeletons. These molecules, which usually serve as communication signals, can change their blend when an individual is compromised, creating a distinct “sickness odor.” This chemical shift acts as an alarm bell, signaling a potential threat to healthy nestmates.
Changes in behavior also provide direct visual and tactile cues. An infected insect may become sluggish, reducing its activity and social interaction within the nest. It may also show atypical or excessive grooming, a visible sign of distress or contamination. These deviations from normal behavior, combined with the altered chemical profile, allow the colony to identify an individual as a risk before the infection becomes highly transmissible.
The Altruistic Act of Self-Isolation
The decision for a sick insect to leave the colony is not random but a profound mechanism driven by kin selection. This behavior is often termed “altruistic self-removal” because the individual sacrifices its own chances of survival for the benefit of its relatives. The colony’s genetic success, or inclusive fitness, is preserved by preventing the pathogen from reaching the queen and the vulnerable brood.
This self-isolation is an active, seemingly suicidal act that occurs before the insect is physically incapable of movement. Studies show that honey bee workers, for example, will abandon their social role and remove themselves from the hive when compromised by toxins or disease. This preventative measure is an effective form of collective disease defense, known as social immunity. By flying away, the sick individual ensures the infectious load is removed from the high-density environment of the nest.
Destinations of the Sick: Leaving the Colony
When a stinging insect is compromised, its journey away from the colony answers the question of where it goes. For worker bees, which are frequently foraging outside the nest, the final act is to simply fly off and not return. They lose the ability to maintain flight altitude in their final moments and land far away from the hive, often miles from the nest structure. This voluntary departure disperses the infectious agent into the environment, away from the concentrated population of the colony.
Insects that become sick or die inside the nest are dealt with through a coordinated behavioral response called necrophoresis. Specialized “undertaker bees” and wasps quickly identify and remove the corpses of their nestmates, a behavior crucial for maintaining hygiene. These undertakers carry the deceased bodies for a significant distance, typically dropping them at least 150 feet away from the hive entrance. This forced ejection ensures the pathogen-laden corpse does not contaminate the nest entrance or the immediate foraging path of healthy members.
Collective Hygiene and Colony Immunity
Even after a sick individual has left, healthy colony members employ several proactive strategies to manage residual contamination. One defense is the use of propolis, a resinous material collected from plants and incorporated into the nest architecture. Propolis contains powerful antimicrobial properties that inhibit the growth of bacteria and fungi within the hive structure. This collective medication creates a sanitized environment that lowers the overall pathogen pressure on the colony.
Colonies also engage in specialized sanitary behaviors focused on the developing brood. Hygienic behaviors include the rapid uncapping and removal of pupae and larvae that have died from disease. Allogrooming, where one insect cleans another, helps remove external spores or mites from the bodies of nestmates. These actions work together to form a robust, multi-layered social immune system, protecting the colony from widespread infection.