  Nonreciprocal interactions break action-reaction symmetry in systems of
interacting bodies. This process inevitably introduces non-Hermitian dynamics
which with its hallmark signature called exceptional points (EPs) has been a
subject of intense research across different disciplines ranging from photonics
to metamaterials. Whether non-Hermiticity and EPs are a fundamental property of
nature and if so, how nature utilizes them to gain competitive advantage have
remained largely unanswered. Although biological systems feature many examples
of non-reciprocal interactions with the potential to drive non-Hermitian
dynamics, these are often theoretically overlooked and not experimentally
investigated. Here, we demonstrate in an active matter composed of social
animal Caenorhabditis elegans and bacteria, non-Hermitian dynamics, and the
emergence of EPs owing to the nonreciprocal nature of oxygen sensing,
nonequilibrium interfacial current, and bacterial consumption. We observed that
when driven through the EP, the system collectively breaks parity-time (PT)
symmetry leading to traveling waves and arrested phase separation. We further
find that these features enable the collective ability to localize interfaces
between broken and exact PT-phases. Remarkably, this ability provides a strong
evolutionary advantage to animals living in soil. Altogether our results
provide mechanistic insights into the detailed symmetries controlling the
collective response of biological systems; answer a long-standing problem; and
give an example of the EP-enabled dynamics in a biological system.
