Emery's rule

Definition

The generalization that social parasites among ants and other social insects tend to be closely related to their hosts, typically belonging to the same genus or to a closely related one. The rule reflects the evolutionary pathway by which social parasitism arises: intraspecific or interspecific social parasites often originate from ancestral populations that diverged recently from their host lineage, exploiting pre-existing chemical and behavioral recognition systems. The pattern appears in both temporary social parasites (e.g., Formica sanguinea group species parasitizing other Formica) and inquilines, though exceptions occur, particularly among slave-making ants that may target more distantly related species.

Etymology

Named for the Italian entomologist Carlo Emery (1848–1925), who first articulated the pattern in 1909 based on comparative studies of ant social parasitism.

Example

The ant genus Myrmica contains numerous inquiline species such as Myrmica microrubra that parasitize congeners; this fits Emery's rule, whereas the slave-maker Polyergus rufescens (Formicinae) raiding Formica hosts represents a looser interpretation, as the tribes diverged earlier.

Synonyms

• Emery's principle

Related Terms

• social parasitism
• inquilinism
• dulosis
• temporary social parasitism
• host-parasite coevolution
• chemosensory mimicry
• myrmecology

Usage Notes

Specialists distinguish 'strict Emery's rule' (parasite and host in same genus) from 'loose Emery's rule' (parasite in related genus or tribe). The rule is probabilistic, not absolute; its predictive power varies with parasite type, being strongest for inquilines and temporary parasites, weaker for some slave-makers. The mechanism—exploitation of shared cuticular hydrocarbon profiles and nestmate recognition cues—explains why distant relatives rarely succeed as social parasites. The term is occasionally extended to non-hymenopteran social insects (termites, aphids) with analogous parasitic systems.