Inland Freshwater Crab (Austrothelphusa transversa)

The Inland Freshwater Crab, scientifically known as Austrothelphusa transversa, is a unique species of freshwater crab native to Australia. Commonly referred to as the inland crab or tropical freshwater crab, this hardy species is well known for its ability to survive in harsh, dry environments and is the most widely distributed member of its genus.

Appearance

These crabs typically display earthy tones such as brown, grey, maroon, or reddish shades that help them blend into their natural surroundings. Adults usually grow to around 5 cm across the shell. Like other freshwater crabs, they have a rounded carapace, four pairs of walking legs, and two claws, with one claw generally larger than the other.

Distribution & Habitat

Inland freshwater crabs are found across much of northern and central Australia. Their range extends throughout Queensland and the Northern Territory, with smaller populations occurring in parts of Western Australia, South Australia, and north-western New South Wales.

They inhabit temporary waterways such as creeks, rivers, floodplains, and waterholes, including regions that experience long dry periods and extreme temperatures.

Adaptations to Dry Conditions

One of the most remarkable traits of this species is its ability to survive drought through a process known as aestivation. During dry seasons, the crab digs deep burrows into mud or clay banks, often reaching depths of 50–100 cm. These burrows help retain moisture and protect the crab from dehydration until rainfall returns and waterways refill.

The entrance to the burrow is sealed with a plug of mud, creating a humid chamber underground where the crab can remain dormant for extended periods.

Amphibious Lifestyle

The inland crab is semi-amphibious and can survive both in water and on land. Its modified gills are capable of functioning similarly to lungs when exposed to air. This adaptation allows the crab to leave shallow pools if water conditions become unsuitable, such as during low oxygen levels or extreme heat.

Out of water, they often shelter beneath leaf litter, roots, or debris to stay cool and moist.

Diet

These crabs are omnivorous scavengers. They primarily feed on algae and plant material that flourish after seasonal rains, but they will also consume decaying organic matter, insects, and small aquatic animals when available.

Reproduction

Female inland freshwater crabs carry their fertilised eggs beneath their abdomen until the young have developed into juvenile crabs. A single female may produce between 100 and 350 eggs.

The young remain protected by the mother during development and are often released after the wet season begins, giving them the best possible chance of survival as waterways refill and food becomes more abundant.