Acetaminophen as an Oral Toxicant for Nile Monitor Lizards (Varanus niloticus) and Burmese Pythons (Python molurus bivittatus)

Context. Invasive species are a growing global problem. Biological invasions can result in numerous harmful impacts on local ecologies, and non-native herpetofauna are frequently ignored. Nile monitor lizards (Varanus niloticus) and Burmese pythons (Pythonmolurus bivittatus, recently reassessed asPython bivittatus bivittatus), have become established in southern Florida. Both are large, semi-aquatic predators that pose serious threats to a variety of threatened and endangered species, as well as to the unique ecology of the area. Aims. Acetaminophen (CAS#103-90-2), a lethal oral toxicant for the invasive brown treesnake (Boiga irregularis) on Guam, was investigated as a possible toxicant in juvenile Burmese pythons and Nile monitors. Methods. Dead neonatal mouse (DNM) baits containing 0, 10, 20, or 40mg acetaminophen were force-fed to Nile monitors, whereas DNM containing doses of 0, 20, 40, or 80mg were freely consumed by Burmese pythons. Subjects were frequently observed post-treatment for general condition and position, with special attention paid to activity (if any), behaviour, respiration, bleeding, emesis, ataxia, and mortality. Key results. InNilemonitors, acetaminophen doses of 10, 20, or 40mg resulted in 0, 50 and 100%mortality, respectively. In Burmese pythons, doses of 20, 40, or 80mg resulted in 14.3, 85.7 and 100% mortality, respectively. No mortality was observed in control individuals of either species. A negative correlation between dosage (mg kg) and time-to-death was observed in both species. Dosages ranging from 522 to 2438mg kg and 263 to 703mg kg were uniformly lethal to monitors and pythons, respectively. Neither species exhibited signs of pain or discomfort following acetaminophen treatment. Conclusions. Acetaminophen is an effective toxicant in juvenile Nile monitors and Burmese pythons. Further investigation into acetaminophen toxicity in adults of these species is merited. Implications. Although further investigation into adult lethal dosages and strategies to optimise bait deployment while minimising secondary hazards is required, acetaminophen may have a role to play in the control of these invasive species in Florida. Additional keywords: acetaminophen, Burmese python, Florida, invasive species, Nile monitor, Python molurus bivittatus, Varanus niloticus.