Chronic pain-like responses revealed by allodynia and hyperalgesia in the ant Lasius niger

Abstract Background Allodynia (pain in response to normally non-noxious stimuli) and hyperalgesia (increased sensitivity to painful stimuli) are well-established indicators of pain sensitization after tissue damage in vertebrates. These phenomena may also offer valuable insights into nociceptive processing in invertebrates. We assessed behavioural evidence for allodynia and hyperalgesia following two types of peripheral injury (tarsus amputation or burning) and sham treatment in black garden ants ( Lasius niger , Hymenoptera: Formicidae). At 20 min, 24 h, and 96 h post-anaesthesia, a ramping hot plate assay with sublethal, but increasingly noxious, temperatures was used to assess allodynia and hyperalgesia. Locomotor speed and proportion of time spent moving were quantified to detect increased responsiveness at normally non-noxious temperatures (allodynia) or exaggerated responses at higher temperatures (hyperalgesia). Results We observed an earlier onset of responsiveness in ants with tarsus amputations and burns compared to controls, consistent with allodynia, which was stronger and more consistent in tarsus-amputated ants and at later time points. Evidence for hyperalgesia was limited and time-dependent: amputated ants showed a steeper response increase at higher temperatures at earlier time points, but not at 96 h. Burn-treated ants showed less consistent evidence of allodynia and no evidence of hyperalgesia. Conclusions These findings suggest that sensitization extends beyond the acute injury phase and align with broader evidence for chronic, pain-like processing in insects. As a new injury model in insects, the burn treatment needs to be refined, or the underlying mechanisms may be different to those involved in classic, amputation-induced sensitization.