Why control possum?

There are good reasons to control possum.

 They are a threat to our ecosystems in many ways:

  • They are opportunists and will eat chicks and eggs in the nest
  • They compete with birds for food, eating leaves, flowers, buds, and fruit.
  • They eat invertebrates such as weta and native snails
  • They damage trees and can cause canopy collapse over time
  • They are significant vectors for bovine TB
  • Around homes, they feed on orchards and gardens.

Background

The possum was introduced to New Zealand from Australia not once but twice. The first release, intended to establish a fur trade, was in the 1830s but was unsuccessful. Sadly, another release was carried out in the 1850s and that was the start of our problems.

By the 1980s there were an estimated 60-70 million possums in New Zealand, the number now is around 30 million.

The possum species we have in New Zealand are the common bushtail possum, Trichosurus vulpecula, they can be grey or black and adults can weigh up to 6.4kg. They are marsupials with mothers carrying their young in a pouch and then on their backs.

Possums are nocturnal, sleeping during the day in dens (often located in tree hollows or roots) and active at night. Their diet is mainly leaves but they will eat chicks, eggs, insects, and small mammals.

The sounds they make range from a sinister-sounding 'he he he' to a loud screech.

Possums live anywhere they can find food and are widespread throughout New Zealand due to their having no natural predators and abundant feed supplies.

Possum fur, pelt, and meat trade

Possum fur is made up of hollow fibres which are both warmer and lighter than wool. This has contributed to a growing market for both fur and pelts. The fur is plucked from dead possums and blended with wool or mohair to create a soft, light fibre used to make clothing.

Pelts are marketed as an alternative to other furs and used to make scarves and throws.

Possum meat is marketed as pet food.

Plucking

If you kill a possum you can pluck the fur off it just like plucking a chicken. This is easy to do when the possum is freshly killed but after about ten minutes it becomes harder to pluck. The valuable fur is the long fur on the back. You don't get much from one possum but with prices over $150/kg, it's worth collecting if you can.

Methods of control

Kill traps

  • Most kill traps work on the same basic principle of a pin holding bait or lure which is attached to a spring. When the bait pin is moved, the spring releases a bar that snaps the possum's neck.
  • Kill traps don't usually attract domestic pets but it's safest to put them out of reach of pets and small children who may be tempted to touch them.
  • If you live in an area with kiwi or weka then traps should be set off the ground, and attached to a tree or post.

Where to put the trap

Place traps where you see signs of possum activity at the base of trees and along possum runs. Runs are the paths the possums use and are often seen as a flat track through grass and under fences.

Bait and lure

Before baiting a trap make sure it has been sprung. Never put your hand in a kill trap without checking, even if there's a dead possum in it!

Some traps use specific baits which are sold as a paste or gel. If you need to improvise then a piece of apple is a good bait for a trap, you can dust it with cinnamon or cloves to make it more attractive to possums. Other baits include citrus fruit and peanut butter and aniseed is supposed to be irresistible to possums.

If you're using fruit as bait then the size of the piece is important, you want the possum to eat the bait directly, not try to grab it. Also, too large a piece of bait can interfere with the mechanism. The recommended amount is equal to about 1/8th of an apple. Never use bait that will attract cats such as meat or fish.

You can make reusable bait by drilling a hole in a small piece of wood and filling the hole with peanut butter. Hook the wood on the bait bar and refill with peanut butter or commercial lure when needed.

To help attract possums to a trap you can mix flour, icing sugar, and ground cinnamon and throw it into and around the trap. The white colour attracts the possum from afar and the scent draws it in.

Setting the trap

Once the bait has been affixed, the trap can be set. Care is needed when setting kill traps as the traps cannot tell a human hand from a possum. Timms traps have a cord at the back to pull to reset the trap, Trapinators use an external lever, other traps you may have to manually reset the spring and hook it to the mechanism.

The Timms trap is the most well-known of the kill traps. Its yellow plastic frame has been a familiar sight for more than 30 years.

The Trapinator trap is designed to be mounted on a tree and has a plastic bait bar on which you spread a bait paste.

Sentinel and Warrier traps are lightweight tree-mounted traps that are ideal for trap lines in larger areas.

Automatic kill traps

With most kill traps you have to reset each time a possum is killed and re-bait frequently. There are alternatives.

The Goodnature automatic possum trap uses a gas cartridge to fire a piston when a possum bites on a lure in the trap. The possum drops out of the trap and it's ready for the next possum. The traps also include a bottle of lure which keeps the trap baited. This trap can kill 12 possums on one gas cartridge. The gas cartridges and lure bottles can be replaced when necessary.

The NZ AutoTraps AT220 automatic trap uses a small battery pack to drop the dead possum and reset the trap. The battery pack should last 12 months and the trap is designed to kill rats and mice as well as possums.

Cage or live capture traps

Cage traps are designed to lure a possum into the trap using bait. When the possum stands on a trigger plate the cage door closes and they are trapped.

Once set, traps should be inspected frequently, at least once a day, and there’s a legal requirement that they be inspected within 12 hours of sunrise the day after they’ve been set.

Any trapped pest animals can then be killed and non-pest animals (like the neighbour’s cat) can be released.

Poison

Poisons are usually used in conjunction with bait stations. They aren't as humane as kill traps and have varying impacts on non-target species such as pets, livestock, and wildlife. Read up on these impacts before you decide to use poison. Bury the carcasses away from waterways and where they can't be dug up by curious dogs.

Poisons you can use without a license include:

Cholecalciferol - a type of vitamin D that is used to treat vitamin deficiency in humans. This is available in gels, paste, and pellet form and is used in bait stations.

Anticoagulants (Brodifacoum and Pindone) - these are available to use in bait stations but you need a controlled substances license to broadcast Pindone.

There are contractors who will provide a possum-killing service who harvest possums for their fur and do not charge for the service. Usually, you will need a substantial number of possums to make it worth their while. It may be worth banding together with neighbouring properties.

Licensed operators for cyanide and 1080

Cyanide and 1080 can be used only by licensed operators trained to make sure they are used effectively with minimum risk to operators, other people, and non-target animals.

The operators publicise the poisoning operation locally and put notices up around poisoned areas, so it is important for animal owners to heed these warnings.

Cyanide

Cyanide capsules and paste (Feratox) kill quickly and humanely when the animal bites into them. The contractor can remove the bait stations very soon after they have been used so there is no residue of cyanide left in the environment.

Dead possums can usually be picked up near the bait station.

1080

1080 is biodegradable when it reaches the ground, but it has the disadvantage of persisting in the stomach of poisoned carcasses, sometimes for months. This means that some animals especially scavengers like dogs are at risk if they eat these carcasses. After eating 1080 in bait, animals can take many hours to die.

Shooting

If you don't have a gun license you can use an air rifle to kill the possum but it should have a velocity of at least 1200fps, any slower and you are likely to wound rather than kill the possum.

With a gun license then a .22 is usually the weapon of choice.

A spotlight and scope are useful to make sure you identify your target and check that the surrounding area is clear.

Possums usually become active a couple of hours after sunset and they're not easily frightened. If you spot a possum it is likely to sit in a tree and look back at you rather than scurry away.

As always before shooting identify your target and calculate where the bullet will go if you miss your target. Don't shoot if there is a danger to people, livestock or neighbouring properties.

Possums are killed by shots to the head. If you hit the shoulder or back the possum may be wounded and it's your responsibility to finish it off. Never pick up a wounded possum – their claws and teeth are sharp and they aren't scared of using them.

If you kill a female possum she may have a young joey in her pouch. If you leave it, you're condemning it to a slow death. It's better to kill it quickly.

If you don't want to shoot possums yourself, it's usually very easy to find a local hunter who is happy to do it for you at no cost. Find someone who has a sensible and responsible attitude to firearms and who will respect your property. There are gun clubs throughout New Zealand and they will be able to suggest suitable people.

Manually killing

Sometimes you may have to kill a caught or wounded possum. It's not pleasant and possums, especially trapped and wounded possums, are dangerous and will attack. It is important that any killing is as humane as possible.

Blow to the head

  • This is not easy and not at all humane unless it’s carried out by a confident, strong, and skilled operator.
  • It usually takes several blows and should be followed up by throat-cutting to ensure death.
  • Don’t attempt this unless the animal is quiet and immobile before the first blow it. If it isn’t it should be restrained.

Gassing

  • Animals in cage traps can be killed by gassing using vehicle exhaust fumes.
  • The fumes must be cool when they reach the cage and they shouldn’t contain acrid fumes.
  • The cage containing the animal can be enclosed in a plastic bag, and the vehicle exhaust (from a cool engine) piped into the bag through a tube long enough to cool the gases well before they reach the cage.
  • Alternatively, the gases can be bubbled through water to cool them.
  • Cars with catalytic converters have reduced CO emissions but their exhaust fumes will still result in euthanasia.

Disposal

Once dead, possums can be buried – if you're planting trees a dead possum in the hole will provide nutrients to the tree.

Trap/bait shy possums

Over time possums become wary of eating bait or entering traps. For this reason, it's a good idea to mix things up a bit over time. If your usual methods suddenly aren't working then it may be time to try something new.

Dogs

The most simple possum control method may be already in your house. Pet and farm dogs are usually great possum control, most love to chase and catch possums. However, they can be injured by the possums.
Assistance

Working with others

Local groups such as Landcare and Community Pest Control organisations can qualify for assistance with pest control. This assistance can include free traps and even money to employ a trapper depending on your area. If you don't have a local group you could look at starting one.

It's also worth talking to your neighbours about possum control. If you work together then you will have a greater impact.