The flightless beetle Merizodus soledadinus, native to the Falkland Islands and southern South America, was introduced to the sub-Antarctic Kerguelen Islands in the early Twentieth Century. Using available literature data, in addition to collecting more than 2000 new survey (presence/absence) records of M. soledadinus over the 1991–2018 period, we confirmed the best estimate of the introduction date of M. soledadinus to the archipelago, and tracked subsequent changes in its abundance and geographical distribution. The range expansion of this flightless insect was initially slow, but has accelerated over the past 2 decades, in parallel with increased local abundance. Human activities may have facilitated further local colonization by M. soledadinus, which is now widespread in the eastern part of the archipelago. This predatory insect is a major threat to the native invertebrate fauna, in particular to the endemic wingless flies Anatalanta aptera and Calycopteryx moseleyi which can be locally eliminated by the beetle. Our distribution data also suggest an accelerating role of climate change in the range expansion of M. soledadinus, with populations now thriving in low altitude habitats. Considering that no control measures, let alone eradication, are practicable, it is essential to limit any further local range expansion of this aggressively invasive insect through human assistance. This study confirms the crucial importance of long term biosurveillance for the detection and monitoring of non-native species and the timely implementation of control measures.

The flightless beetle Merizodus soledadinus, originating from the Falkland Islands, was introduced to the sub-Antarctic Kerguelen Islands. We compiled the existing information on ship visits and landings on these islands to confirm the introduction date of M. soledadinus. Using data available in the literature, in addition to collecting more than 2000 presence/absence records of M. soledadinus over the 1991-2018 period, we tracked changes of its abundance and geographical distribution. The range expansion of this nonflying insect was initially slow, but has accelerated over the past two decades in parallel to local increased abundances of the insect's populations. Human activities may have facilitated colonization of some localities by M. soledadinus which is now widely present in the eastern part of the Kerguelen archipelago. This predatory insect represents a major threat for the native invertebrate fauna; in particular, the wingless flies Anatalanta aptera and Calycopteryx moseleyi which are locally displaced and/or eliminated by the beetle. If no control measures, let alone eradication, are practicable, it is essential to limit the transport of this invasive insect along with human activities. Since 2006, the Kerguelen Islands have had the status of a nature reserve, making these results of significant interests for the management of this archipelago, and more generally, emphasizing the importance of long-term biomonitoring programmes for assessing and predicting changes in the distribution of invasive organisms. Strict biosecurity measures have now been established at the Kerguelen Islands, with even greater attention paid to visits to remote sites not yet colonized by M. soledadinus.