Social Parasitism

By: Aya Hilal

A couple of days ago, my friends and I watched the movie Parasite together. We all absolutely loved it- the dark but comedic tone kept us captivated, and the character moments placed throughout the film spurred a conversation that lasted for hours. Afterwards, however, the symbolism in the movie alluding to a toxic symbiotic relationship had me wondering: does social parasitism exist? What instances of it occur in the natural world? Luckily, I got my answer.

Insects are quite unique in the sense that they exhibit various degrees of social behavior. Social insects (such as termites, ants, some bees, and some wasps) live cooperatively, carrying out tasks together and serving their colony as a cohesive unit. They search for food together, band together in order to defend their home, and often outcompete other insects, giving them an evolutionary advantage. Many social insect colonies are divided into ‘castes’, with groups of insects working to fulfill a specific role. Social parasites—insects that have evolved to shortcut typical social insect behavior—are interesting because they deviate from these norms; .they receive the benefits of living in a colony but do not participate whereas true social insects are considered eusocial.

Although this type of parasitism is still being studied, examples of behaviors that social parasites exhibit have been documented. Ants are typically cited when discussing social parasitism, as they have been recorded to transition into mixed species nests where the parasitic ants depend on the labor of the host ants. Socially parasitic ants have also been noted to be ‘slave-makers’. Slave-makers steal a brood from a colony and bring the larvae back to their nest, exploiting them unwittingly for labor. These parasites have also developed adaptations that assist in slave-raiding. Another method of social parasitism in ants is temporary social parasitism. Throughout the establishment of a new colony, parasitic queens will attempt to infiltrate a host colony, replace the original queens, and lay eggs that eventually become parasitic offspring. When the host workers who previously accepted the parasitic queens die, the only ants left in the colony will be the parasites, thus promoting the maturation of a colony through infiltration.

In 1909, a taxonomist named Carlo Emery developed a rule regarding social parasitism in insects. Emery’s Rule posits that social parasites and their hosts are often closely related to each other. A reasoning for this is that parasites and hosts in the same subfamilies have similar pheromones and communication systems, thus making parasitism more accessible. Ants have been observed to typically be enslaved by members of the same subfamilies, fulfilling this rule.

Social insects are extremely complex and variable in their degree of social behavior. Their colonies are often intricate in each ant’s role and function, splitting up into castes and stations. Social parasites are fascinating because they infiltrate seemingly unbreakable defenses from the inside.


What Did You Learn?


1. What is Emery’s Rule?

In 1909, a taxonomist named Carlo Emery developed a rule regarding social parasitism in insects.