Quokkas are going viral again - a photo of the Australian marsupial seemingly asking for a hug has drawn ardent fans on Instagram. They previously shot to fame in 2013.

The apparent smile of the herbivore, found only in Australia, is testament to its Internet title of "the happiest animal on earth".

Now to get to know the critters better:

1. They are the only mammal native to Rottnest Island, which was named after them

The quokka (pronounced kwoh-ka) is found mainly on Rottnest Island, where its numbers range from 8,000 to 12,000.

Only a few hundred wild quokkas live outside of the island, on the Australian mainland, according to a 2016 video by Rottnest Island.

Rottnest Island was reportedly named after quokkas, which Dutch mariner Willem de Vlamingh thought looked like giant rats. "Rotte nest" is Dutch for "rat nest".

In 1696, Mr de Vlamingh described the quokka as "a kind of rat as big as a common cat".

It was first observed by another Dutch mariner, Mr Samuel Volckertzoon, in 1658, and was reportedly the first Australian animal to be recorded by Europeans.

2. They are herbivorous, nocturnal marsupials

The quokka is a marsupial from the same family as kangaroos and wallabies, but is the only member of the genus Setonix, known locally as the Kangaroo Rat.

It is about the size of a cat, growing up to 54cm in length and weighing 2.7kg to 4.2kg.

The nocturnal creatures are herbivorous, feeding on tree and shrub buds and leaves, grasses, succulents, seeds and roots.

Female quokkas suckle their young in a pouch, like kangaroos, for about six months. Wild quokkas can live for up to a decade.

3. They are listed as vulnerable

Quokkas are listed as "vulnerable" on the IUCN Red List Of Threatened Species, which tracks the conservation statuses of animals around the world.

Threats to the animal include habitat clearing, foxes and feral cats, as well as burning and clearing of forested habitats, according to the International Union for Conservation of Nature.

The creatures are also affected when humans feed them, as this can change their diet and behaviour. Visitors to Rottnest Island are reminded in a promotional video on the island's website not to feed or touch the quokkas.

4. They were named 'the happiest animal on earth' in 2013

In 2013, quokkas were given the title of "happiest animal on earth" by The Huffington Post in a report that went viral.

The critters are friendly to people, judging by the thousands of selfies people have taken with them. A hashtag #quokkaselfie has more than 11,000 entries on Instagram, many depicting smiling quokkas.

They have been said to be unafraid of humans as they have few natural predators and have been known to approach people out of curiosity.

Foxes are one of their biggest enemies but fox control programmes have contributed to their rise in numbers. Quokkas are protected animals on Rottnest Island, with heavy fines for those who "interfere with" - including feeding - them and up to five years' jail for those found guilty of cruelty against them.

5. They have a 'dark side' too - ejecting their young from pouches when threatened

According to a research paper published in the Wildlife Research journal in 2005, female quokkas may eject offspring from their pouches when threatened by predators.

The article, titled Mortality And Survivorship Of The Quokka (Setonix Brachyurus) (Macropodidae: Marsupialia) In The Northern Jarrah Forest Of Western Australia, said: "When a female quokka becomes aware of a life-threatening interaction with a predator, she may expel her offspring whose subsequent noise attracts the attention of the approaching predator."

The baby would flounder on the ground and hiss loudly.

Such behaviour has been observed in other marsupials such as grey kangaroos and swamp wallabies.

6. A quokka once predicted Australian Prime Minister Malcolm Turnbull's election victory

In June 2016, a quokka named Davey was made to choose between two jars of eucalyptus leaves at Wild Life Sydney Zoo.

One was labelled Turnbull and the other Shorten.

Mr Malcolm Turnbull's Liberal party-led coalition was up against Mr Bill Shorten's opposition Labor in an election race.

Davey chose Prime Minister Turnbull's jar and the rest is history.

SOURCES: Discoveraustralia.com, Iucnredlist.org, Reuters, Rottnestisland.com, Thedodo.com