Walking through Ballaugh Curraghs, a marshland in the north of the island, I’m taking part in a favourite island pastime: spotting red-necked wallabies. Creeping through the stands of willows, I soon see a grey shape with beady eyes and pricked up ears watching me, unafraid. Another appears and I check for the ultimate sighting … a joey poking out from a pouch, but without success. It’s a rare sight even here.

These marsupials have changed this area beyond recognition. They arrived in the 1960s after a few escaped from a nearby wildlife park, and even by 2006 their footprint was light enough that the “curraghs” were declared a wetland site of international importance. Today, though, it would struggle to qualify, as so many key species have been eaten or disturbed by the 800 or so wallabies that now dominate.

To many Manx residents they are lovable creatures. Wallaby pictures appear in social media posts, and are featured in journals worldwide. But their popularity is on the wane, as people learn the downside of their numbers. Cute wallabies are vectors of toxoplasmosis, a parasite that can cause spontaneous abortion in women, while liver fluke has been found in postmortems of animals hit by cars. A string of accidents caused by people swerving to avoid wallabies has been reported, and the fear of one hopping in front of a high-speed TT rider is a nightmare for race organisers.

Their effect on the natural environment is also a concern. The part of the curraghs I walked through is dense willow, but the understorey of rare plants including royal fern and common wintergreen was absent, nibbled to the soil. I should have seen vegetation below a metre, ivy, angelica and meadowsweet, but saw none. Nearby, a huge field that used to host a winter roost of more than 100 hen harriers was recently found to have hundreds of wallabies grazing nightly, while the birds are gone. Nor are the wallabies themselves thriving despite their growing population, suffering from inbreeding and a poor diet.

What can be done? Manx Wildlife Trust is putting together a management policy that balances animal welfare, economic concerns and local ecosystems, but one thing’s for sure, our island’s wallabies are likely here to stay.