Earwig mothers employ a suite of hygienic behaviors to defend their nest against microbial threats

Hygienic behavior is a key defense against pathogens in mammals and birds,
yet it remains surprisingly understudied in insects outside eusocial
species. This gap raises the questions of whether such behaviors are
unique to eusocial insects or instead reflect widespread forms of social
immunity that may have shaped the evolution of insect sociality. Here, we
investigated hygienic behavior in the European earwig, a non-eusocial
insect exhibiting maternal egg care. First, we exposed pre-ovipositing
females and males to organic (microbial risk) and plastic items, and found
that only females selectively covered organic items, starting at
oviposition. We then introduced either an organic item, an organic item
with pathogen spores, a plastic item, or no item into female nests
post-oviposition. Mothers continued to cover organic items and
consistently relocated their eggs away from them, regardless of the
presence of pathogen spores. Nest architecture remained unaffected by item
type. Altogether, these findings reveal advanced hygienic behaviors in a
non-eusocial insect, confirming that certain forms of social immunity can
evolve independently of eusociality and reproductive division of labor.
These findings highlight how parental care could have been a pivotal step
in the evolutionary trajectory toward the sophisticated disease defenses
seen in more complex insect societies.