Cane toads are a highly invasive species and are regarded as a major environmental pest in Australia. While there is fairly universal agreement over the need to control cane toads, there is significant debate over what is the most humane method to use. This is largely due to the limited research into the impact of killing methods on toads, compounded by the fact that it is difficult to measure pain and distress in amphibians through observation alone.
Despite this, thousands of cane toads are killed every year in Australia by government and community groups and individuals, using many different (and sometimes inhumane) methods. Irrespective of the fact that cane toads are considered pests, they are also capable of experiencing pain and distress and so any measures to control them must not cause suffering. It is the responsibility of both the government and the community to ensure that only humane methods are used.
The unfortunate reality is that there are very limited humane practical methods available for use by the general public. Most currently recommended methods either require special equipment or operators to be trained and skilled. To this end, community based training programs on humane killing would help to ensure that members of the public were able to learn safe, effective and acceptable techniques.
What killing methods are being recommended?
Detailed information on the humane killing of cane toads is available in the Australian Government publication, Standard Operating Procedure for the Humane Field Euthanasia of Cane Toads (SOP) which has been based on a comparative study of the humaneness of a range of different cane toad killing methods.
No methods are listed in the SOP as unconditionally acceptable, but there are three methods listed as conditionally acceptable. These are:
(a) spraying with Hopstop®;
(b) stunning followed by decapitation and;
(c) prolonged exposure to carbon dioxide.
A further method, cooling followed by freezing, is listed as not acceptable in the SOP, however, recent research suggests that this method may be more humane than previously thought and may be the most humane and reliable method for untrained people where Hopstop® is unavailable.
The following methods can be used without formal training:
- Hopstop® is an aerosol spray that has been specifically developed for killing cane toads and is commercially available for this purpose. When applied in sufficient quantity it appears to be an effective, easy to use and relatively humane method. Information on where to purchase Hopstop® is provided through the manufacturer’s website: www.pestat.com.au/html/products.htm. It is very important that each toad is treated with sufficient spray to ensure death. The SOP recommends that after spraying, the toad is closely observed and once movement ceases, a second spray must be applied. Two hours after spraying, toads must be checked for signs of death before disposal. Gloves must be worn when handling cane toads.
- Cooling followed by freezing is another option if Hopstop® is not available or accessible, with new research indicating that this might be more humane than other methods (Shine et al. 2015). However, further research is needed to confirm that the ‘cooling’ phase is humane. This method involves two steps – firstly, always wear rubber gloves when handling toads; toads should be placed in a plastic bag and then in a container (labelled) and placed in the refrigerator for at least 12 hours to allow loss of consciousness. Then once the toad is checked that it is no longer moving, it can be placed in a freezer for 24 hours, after this time, it must be checked that death has occurred and once confirmed dead, it can be disposed of.
The following methods MUST ONLY be used by trained and competent operators:
- Stunning followed by decapitation can also be used to kill individual cane toads, but this method is only suitable for use by confident and skilled operators with the correct equipment and technique. This method must not be used unless those involved have received appropriate training, as ineffective stunning or unskilled decapitation will result in an inhumane death.
- Prolonged exposure to carbon dioxide is the most commonly used method for killing multiple cane toads at a time. This method must only be used by trained operators using appropriate equipment. Death must be confirmed prior to disposal.
For further information on the above methods, please read the SOP.
The SOP also states that the disinfectant Dettol® must not be used to kill cane toads as it is inhumane.
The establishment of cane toad control centres where the public can deliver toads for humane killing by trained operators would help prevent inhumane methods being used as well as assist people who are unable to kill cane toads themselves. Such centres would require community and government support.
It is also recommended that research be undertaken to assess the suitability of a specialised small captive bolt (e.g. poultry or rabbit stunner) for stunning prior to humane killing.
How do I know when a cane toad is dead?
When using any killing method, it is essential to confirm that the animal has died before disposing of its body. Determining death can be difficult with amphibians as their heart rate is difficult to detect and respiration can occur through the skin as well as the lungs. Absence of all of the following signs will confirm that the cane toad is dead (remember to wear thick plastic gloves when handling cane toads):
- Loss of righting reflex – the toad cannot turn itself over when placed onto its back
- Loss of withdrawal reflex – no response to a light squeezing of the skin in between the toes
- Loss of deep pain reflex – no response to moderate squeezing of the toes
- No respiratory movement – no throat movements that indicate breathing
- No heart activity – no chest movement or visible pulse
Always check for these signs and do not assume an animal is dead just because it is not moving or apparently not breathing. If any of these signs are detected, then the killing procedure must be repeated.
Sharp T, Lothian A, Munn A & Saunders G (2011). Methods for the Field Euthanasia of Cane Toads: CAN001. Canberra, ACT: Department of Sustainability, Environment, Water Population and Communities. Available from http://nrmonline.nrm.gov.au/catalog/mql:2853.
Shine R, Amiel J, Munn A, Stewart M, Vyssotski AL and Lesku JA (2015) Is ‘cooling then freezing’ a humane way to kill amphibians and reptiles? Biology Open 00, 1-4 doi:10.1242/bio.012179.