  We present a quantitative method, utilising a highly sensitive quantum
sensor, that extends applicability of magnetorelaxometry to biological samples
at physiological temperature. The observed magnetic fields allow for
non-invasive determination of physical properties of magnetic materials and
their surrounding environment inside the specimen. The method is applied to
American cockroaches and reveals magnetic deposits with strikingly different
behaviour in alive and dead insects. We discuss consequences of this finding to
cockroach magneto-reception. To our knowledge, this work represents the first
characterisation of the magnetisation dynamics in live insects and helps to
connect results from behavioural experiments on insects in magnetic fields with
characterisation of magnetic materials in their corpses.
