Soldier crabs, Mictyris longicarpus, are approximately 1.5 cm wide. Their body is small, spherical, and blue. They have purple stripes on their lengthy jointed legs. It receives its name from two characteristics: its tendency for mass transit and its ability to walk forward rather than sideways. “This species travels in large groups of crabs known as ‘armies.’ This crab is the only member of its species capable of walking forward rather than sideways.” It is unclear why soldier crabs march. They are not feeding, but they could be scouting for feeding grounds.

Why do crabs burrow in sand?

Mictyris longicarpus spends most of its time buried in sand. Although some individuals may remain buried for the whole tidal cycle, they come to the surface a few hours before low tide. The emergence of “hummocks” on the surface of the sand that grow over a period of 10–30 minutes is the first clue that a crab may emerge. Temperature, wind, and rainfall influence the number of crabs that emerge, with various sexes responding differently. For example, one day, all the crabs that emerge are male, but the next day, there may be a mix of males and females. The emergence of a population from the sand can take up to an hour or as little as five minutes, with adults appearing before youngsters in most cases.

Breathing on the ground

They can breathe outside of the water by producing bubbles to keep their gills moist, allowing them to transfer oxygen to their blood. This approach is frequently employed outside of water for brief durations of time. Crabs need to breathe air for extended lengths of time while they are not in the water.

Crabs that have adapted to life on land, such as the coconut crab and the black-backed land crab, may breathe air through their gills without requiring water in their gill chamber. These crabs may also absorb oxygen through the lining of their gill chambers.

What causes soldier crabs to drown?

Light-blue soldier crabs (Mictyris longicarpus) have both lungs and gills (albeit only five gills). Their lungs provide 90% of their oxygen. They drown when their tunnel collapses during high tide and ocean water fills it.

They cannot stay submerged for lengthy periods of time because they are air-breathing crabs.

Crabs that have evolved to life on land still have gills to receive oxygen from water, but their stiff form prevents them from collapsing in air, resulting in a smaller surface area that cannot extract enough oxygen from water — leading to drowning if immersed for too long!

The black-backed land crab, for example, cannot survive in water for more than 18 hours. Other crabs, such as the blue land crab and the shore crab, can breathe on land and in water equally well. Crabs are fascinating creatures with a diverse repertoire and adaptability to different environments when it comes to breathing.