An echidna’s to-do list: Sleep. Eat. Dig up Australia.

With no nipples and reptilelike eggs, short-beaked echidnas look like a first draft of a mammal. Yet, as Australia’s other digging mammals decline from invasive predators, the well-defended echidna is getting new love as an ecosystem engineer.

The only mammals today that lay eggs are the four echidna species and the duck-billed platypus. Eggs are probably a holdover from the time before mammals split from reptiles. Each year or so, the short-beaked echidna (Tachyglossus aculeatus) lays one leathery egg “about the size of a grape,” says Christine Cooper of Curtin University in Perth. Instead of constructing a nest, mom deposits the egg in her version of a kangaroo pouch and waddles around with it.

When the egg hatches about 10 days later, two patches of pores in mom’s pouch ooze milk, and the baby laps it off her skin. The puggle, as a baby echidna is called, hitchhikes for weeks as mom forages. The ride ends, however, when the puggle starts growing spines. “Then mum’s like, ‘Nope, no more,’ and she will put [baby] into a burrow,” Cooper says.

Foraging echidnas claw around and poke their snouts into termite or ant nests, flicking out a long gooey tongue to flypaper up insects. The goo comes from unusually large salivary glands, but a quick echidna lick doesn’t slime. When Cooper wears sandals to visit captive echidnas, she says, “it’s ‘ooh, that tickles!’ ”

Echidnas’ toes point backward on their hind paws but forward on the front, and their short legs slant outward in a bit of a reptile sprawl, says Christofer Clemente of University of the Sunshine Coast in Sippy Downs, Australia. They rock side to side as they walk, moving both left, then both right feet. They can’t run, but they’re strong diggers, Clemente says. They not only claw around for food, but also defend their soft undersides by quick-digging into the ground, spikes up.

Acceleration-sensing instruments strapped onto short-beaked echidnas show they spend about 12 percent of their day excavating, researchers report in the Oct. 15 Journal of Experimental Biology. Over a year, a single echidna churns up some 204 cubic meters of soil, the scientists calculate, as it hunts for insects or scrabbles for shelter.  That’s enough to bury more than 100 full-sized fridges. 

That digging benefits the echidna’s unusual diversity of habitat — from rainforest to desert. Echidnas don’t need to bury fridges, but soil turnover and nutrient mixing keep ecosystems humming along.