Goannas as predators of koalas

Goannas (varanids), also known as monitor lizards, include the list of koala predators. There are more than 50 species of goannas worldwide, and about 25 of them are found in Australia. Among these 25 species, three of them, such as Varanus giganteus, Varanus rosenbergi, and Varanus varius, are the ones that eat mammals (including koalas), eggs, birds, and other reptiles. These species of goannas have large-sized gapes that allow them to swallow large-sized prey such as koalas. However, very large-sized prey is often turned into pieces and then consumed in episodes. Their teeth are large, sharp, and recurved which allows them to hunt their prey with ease.

Young koala joeys on the ground that have been separated from their mothers are the prime targets of goannas. However, the hunting capability of these goannas may not be ignored in the trees as well. There hasn't been any record of goannas preying on a fully grown adult koala but any ailing or old koala can easily become their victim too.

Size of top Australian goannas that hunt koalas

Species	Length	Weight
Varnus Giganteus	2.5 meters	40 Kg
Varnus Varius	2.0 meters	15 Kg
Varnus Rosenbergi	1.5 meters	4.0 Kg

When a goanna is on a hunt, it moves in a swinging gait fashion while keeping their snout as close to the ground as possible. Their fork-shaped tongue flickers in and out which helps them to detect the exact position of some potential prey. This way they can easily detect a koala on the ground or tree as well. Their bite is very lethal as it causes bacterial infections causing a larger prey to have a slower death. However, small preys like koala joeys may even be consumed directly by them.

Some species of goannas can grow very huge and long, i.e., Varanus giganteus that can grow from 2.5 to 3 meters long and can weigh about 40 kilograms. This goanna is found in Western Australia, Southern Australia, the Northern territory, and Queensland. Koalas are also found in Southern Australia and Queensland; therefore, they do become victims of these goannas.

Similarly, Varnus varius goanna is found in Queensland, New South Wales, Victoria, and South Australia. All of these regions have koalas and these gonnas predate on koalas on any given opportunity. Varnus goanna can grow up to 2 meters long and they may weigh up to 15 kilograms. Varnus varius are also called lace monitor or tree goanna.

Another very huge species of goannas is Varanus rosenbergi which can grow up to 1.5 meters in length and weigh about 4 kilograms. These goannas are found in the Australian Capital Territory, New South Wales, Victoria, and Western Australia. Young koala joeys from the Australian Capital Territory, Victoria, and New South Wales may well be predated by Varnus rosenbergi.

Lastly, since both goannas and koalas are native to the Australian continent, goannas are indeed the indigenous predators of koalas. They have been hunting mammals (including koalas) for millions of years on the Australian continent.

References

1. King, D. and Green, B., 1999. Goannas: The Biology of Varanid Lizards. UNSW Press.
2. Atkins, B. and Mitchell, S., 12. The Koala Genome Project: What is a genome anyway.