Small invaders, big risks? Nine years of invertebrate interceptions in Australian Biosecurity

The introduction of non-native invertebrates poses a significant threat to Australia’s environment, biodiversity, agricultural industries, and socio-economic wellbeing, necessitating robust biosecurity measures to prevent their establishment. We examined nine-years of invertebrate interceptions (2016–2024) at Australian borders, providing valuable insights into trends in interception frequency, taxonomic diversity and transport pathways. We identified seasonal fluctuations in detection frequency, with invertebrates most frequently intercepted between November and February. Interceptions decreased significantly in 2020, likely due to the international border closure as a result of COVID-19. While 2,414 unique species were identified, only 40.5% of intercepted specimens were identified to species level. It is procedurally common for species to remain unidentified if their higher taxa have no known biosecurity risks in Australia; however, we were unable to distinguish such deliberate instances from occasions where taxa were genuinely unidentifiable (e.g., undescribed species). The diversity of intercepted invertebrates differed moderately each year, but overall Tetranychus spp. were the most frequently intercepted taxa. Over the nine years, the diversity of intercepted and identified species continued to increase, showing no signs of plateauing. This underscores the need for ongoing surveillance, efficient taxonomic identification, and standardised data collection across Australia. Our findings reveal that interceptions are influenced by commodities of trade, mail transport, passenger movement, and trade in live wildlife, including the smuggling of exotic pet species. We recommend continued enhancements to biosecurity protocols, including more comprehensive interception records, the integration of a nation-wide standardised taxonomic database, and resources to support rapid risk assessments of new emerging non-native species, to strengthen Australia’s existing ability to mitigate the risks associated with invasive invertebrates.