Introduction to Isopods
Isopods are a remarkably diverse group of crustaceans, thriving in nearly every corner of the planet. From the mysterious depths of the ocean, where giant isopods and the formidable giant Antarctic isopod roam the sea floor, to the familiar leaf litter of our gardens, home to terrestrial isopods like pill bugs and woodlice, these creatures have adapted to a stunning variety of environments. The name “isopod” comes from the Greek for “equal foot,” a nod to their seven pairs of jointed limbs that give them a distinctive, uniform appearance.
With over 10,000 known species, isopods can be found in marine, freshwater, and terrestrial habitats. Marine isopods inhabit everything from shallow tide pools to the deepest ocean trenches, while freshwater species make their homes in rivers, lakes, and wetlands. On land, terrestrial isopods have evolved clever ways to conserve moisture, allowing them to survive in environments that would challenge most other crustaceans. These land isopods are closely related to crabs and lobsters, yet have developed unique adaptations to thrive away from water.
Isopods are built with three main body segments—the head, thorax, and abdomen—and their seven pairs of legs are attached to the thorax. Females possess a specialized brood pouch, or marsupium, on their underside, where they nurture their developing eggs. During the breeding cycle, a female releases aggregate pheromones to attract male suitors, and can store sperm from multiple partners, giving her flexibility in fertilizing her eggs during each receptive period. For more on how to distinguish males from females, check out our expert guide.
The feeding habits of isopods are as varied as their habitats. Some are scavengers, breaking down decaying matter and recycling nutrients, while others are filter feeders, predators, or even parasites—certain species have evolved to live in close association with hermit crabs or other marine animals. The suborder Asellota, for example, includes species that have adapted to extreme environments, such as the deep sea or polar regions.
Young isopods, called mancas, remain hidden in safe places like burrows or under leaf litter until they are ready to face the world. Throughout their life cycle, isopods play a vital role in ecosystems, serving as both prey and predator, and helping to maintain the balance of their environments. Their fascinating diversity and adaptability continue to intrigue scientists and naturalists, making isopods a truly captivating subject in the world of crustaceans.
What came first the isopod or the egg?
At risk of turning this article into a biology lesson, the lifecycle of an isopod begins with a male and female isopod in a synchronised courtship. Typically, the isopod breeding season begins in the spring, however, isopod breeding depends less on the time of year and more upon the right habitat.
If the habitat is right, the female enters a receptive period where she will form a pair and mate with a male. During this receptive period, the female releases aggregate pheromones to attract male suitors.
Adult isopods can reproduce for several seasons. On average, they live for approximately a year and a half. However, some individuals can live for two years or more. Mortality rates are higher in animals that have been isolated from other isopods, suggesting that social behaviour is important for their survival.
Both males and females' mate with multiple partners, and females can store sperm from several different males for later use. She can store sperm for an entire year to use in the next breeding cycle.
And so the cycle begins: eggs hatch…
After mating, the female produces eggs. Unlike their aquatic pod relatives, land isopods utilize a unique structure known as a marsupium.
The marsupium is a fluid-filled pouch on the female's underside which she uses to brood her eggs.
During the brooding phase the mother seeks out a burrow. The female broods the eggs within her marsupium for a period of two or three months. Once the eggs hatch, the young can remain inside the marsupium for an additional three or four days. The young offspring are known as mancas and they have 6 pairs of legs during this phase of their life.
Typically, the mother remains hidden in the burrow until her young emerge from the marsupium with up to 200 babies. The young isopods remain hidden within the burrow until they have molted several times, growing into juveniles and growing 7 pairs of legs. Once they have completed enough molts, their armour stiffens to protect them from harm and they are ready to leave the burrow.
Once they reach between two and three months of age they are ready to reproduce themselves.
And so the cycle continues…