National Wildlife Research Center NWRC)
Brown Treesnake Research at NWRC
Repellents and Irritants
Identifying a safe, easily applied, and effective method for driving brown treesnakes from cargo pallets and containers has long been an operational priority for reducing the threat of transport of these snakes from Guam. Irritants are important for driving brown treesnakes from areas where they can easily be concealed, such as cargo areas and transport vessels. For example, when Wildlife Services personnel began working with snake-detecting dogs in Guam, though a dog would indicate the presence of a snake in the cargo, there was be no easy way to drive the snake from its hiding place making it difficult to ensure that shipments were snake-free.
In the ongoing search for effective treesnake repellents, several criteria are important:
- methods must meet EPA regulations for human health and safety and environmental safety,
- methods must not interfere with other interdiction methods,
- candidate methods or compounds must not leave a lasting odor or degrade the materials they come in contact with, and
- the irritant or repellent must be economical and easily applied to cargo.
NWRC scientists have been looking at natural products as repellents. Most of these products have been approved by the U.S. Food and Drug Administration for human consumption. These compounds require minimal support data and do not require registration by the U.S. Environmental Protection Agency because they are already listed as safe by the Agency. Recent compounds tested, such as cinnamon oil, clove oil, and eugenol are now available for use. These compounds are considered environmentally benign and require no registration at all. Some of the compounds tested seem to uniquely affect snakes and do not appear to affect mammals or birds.
Recent research efforts focused on identifying irritant chemicals that could be sprayed or blown into containers to elicit the exit of brown treesnakes have met with a number of difficulties that make effective operational application of such an approach doubtful. In contrast, laboratory trials show that directed currents of warmed air quickly cause brown treesnakes to exit refugia. Laboratory trials are completed and are being analyzed to identify duration and delivery temperature of warmed air to reliably elicit exit of snakes from experimental refugia under varying conditions of passageway length and composition. Once these delivery temperatures and times-to-exit are identified, it will then become necessary to prove the utility of this method in operational field situations using real cargo pallets and containers. The goal of this work is to identify delivery times and temperatures needed to drive snakes from real cargo pallets and thereby demonstrate the utility of active heat treatment as an effective means to remove brown treesnakes from the cargo network.