Mictyris longicarpus  (Soldier Crab)


Phylum: Arthropoda
Class: Crustacea
Order: Decapoda
Family: Mictyridae

Geographic Range

This particular species is indigenous to eastern Australia. Even though the soldier crab can be found inhabiting certain areas of predominantly eastern Australia, it can be found in other areas as well. The predominant areas stretch between Queensland to New South Wales and again from Victoria to Tasmania.

Physical Characteristics

Mictyris longicarpus has a very distinctive light blue colored shell with some aqua to green in it as well. When looking at these creatures, you will notice their joints are reddish in color within the legs. These tiny legs have some decalcified areas in each which allow them to absorb small amounts of oxygen that aids in their respiration process. Soldier crabs have been known to reach sizes larger than 25mm as well.

Natural History

Food Habits

Soldier crabs usually tend to eat detritus as their main source of food in their intertidal habitats. Therefore these creatures are known as detritavores. Detritus is defined as "Accumulated organic debris from dead organisms, often an important source of nutrients in a food web." (Detritus) Soldier crabs will comb the sandy intertidal zones scooping up this debris with their front claws and eating it. The crabs will then deposit the waste sand that is left over in compacted balls called pseudofaece. When we have a look at the other end of the food chain and/or food web, soldier crabs are the prey of much larger animals such as the heron and the ibis.


Soldier crabs reproduce through means of copulation. The female can hold the male's sperm inside her until she releases the eggs. At this time the saved sperm fertilizes the eggs. Females will hold the eggs under her in a sponge-like mass until they are ready to hatch.


This species travels in large numbers of crabs, which have been named "armies". This type of crab is the sole member of its species that is able to walk forwards instead of the typical sideways motion we see in other crabs. When threatened, these soldier crabs begin to burrow themselves into the sandy beaches in a sideways corkscrew-like motion. This motion is mostly in the counterclockwise direction, but some have been seen to burrow in a clockwise direction. This burrowing into the sand increases the oxygenation within the sediments. This is known as bioturbation.


Soldier Crabs live predominantly on the sandy intertidal shore areas of eastern Australia. These areas have little wave action, but are constantly changing due to tidal activity and other erosion factors. Soldier crabs are typically found near the mangrove communities which provide adequate shelter and some protection for them. The wet and muddy nature of the sands allows for these crabs to make a quick retreat into a newly formed burrow when threatened in any way. Since the areas that these crabs are found in are low energy shorelines, they can become very abundant. Since these crabs can not burrow down into the ground where sea grass in present they tend to have a mutually exclusive relationship with seagrass.


As far as we know, the soldier crab is not an endangered species.

Economic Benefits for Humans


One benefit of having Soldier crabs around is that they are scavengers. They feed off of the dead remains of animals on the beach and clean it up.


The Soldier crab is a marvel to see with their beautiful lively color and behavior when travelling in their 'armies'. These creatures are a wonder to watch and are a recommended creature to keep an eye out for. That is if they do not burrow their way out of sight first. In the United States of America, our "hermit crab" is also referred to as a "soldier crab". This could cause confusion depending on who you are talking to about soldier crabs. Australians understand the "soldier crab" to be the one shown in the illustration at the beginning of this report.

References and Links

Reference: Davie, Peter et al. Wild Guide to Moreton Bay. Queensland Museum. 1998. pp. 101.

Reference: Detritus

Reference URL: http://sc.cartage.org.lb/dict/Ecological/1text/Detritus%20.html

Reference: Soldier crab

Reference URL: http://mangrove.nus.edu.sg/guidebooks/text/2025.htm

Reference: Taxonomy

Reference URL: www.encyclopedia.com

Image Source

Reference: Soldier Crab

Reference URL: http://www.colours.dk/anders/dyk/soldiercrab.jpg

Entry Author: Jason Nackley Hobart College 2002

Hobart & William Smith Colleges and Union College
Partnership for Global Education: Queensland Term 2001