Are Isopods Insects?

 No, isopods are more closely related to crabs than insects, these little crustaceans evolved to live on land hundreds of millions of years ago, with many other species of isopods staying in the oceans, and some moving into freshwater.

 Isopods may all look similar, but there is a huge variation between species, from the tiny Microcerberidae growing to less than 2mm, through to the Giant Isopods growing to 50cm at least, with much larger examples being reported, but never proven. They occupy nearly every ecological niche you can imagine, some are carnivores, some live on decaying vegetation, and others on the waste on the floor of a cave.

The lifecycle of an isopod is fascinating, starting as a manca, the plural is mancae, which just means the first stage after the female releases them. These baby isopods initially look like mini-adults, but they only have 6 pairs of legs, as they grow and moult they will grow their seventh pair.

 At this point, some isopod mothers consider their job done and will leave the young, but other species have been known to defend their new little mancae. Isopods have surprisingly complex social dynamics for something that we don't really consider to be a 'proper' animal. Desert-dwelling isopods are known to dig complex burrows and protect the young within, constructing walls of their own poop to show other isopods where their territory is. They're also monogamous and only have one litter of mancae in their lifetime.

 As they grow isopods will get too big for their exoskeletons. Unlike us with an internal support structure that grows as we do, crustaceans are stuck in a shell that remains the same size. To allow them to grow creatures with an exoskeleton will moult or shed their outlayer. The new exoskeleton will need some time to harden, making them more vulnerable to attack. Isopods are the only type of crustacean to shed their exoskeleton in two parts. First, they lose the back half, and then the front.

 In the wild, there are plenty of predators willing to snack on an isopod, including specialist predators that have evolved to feed on them, such as the woodlouse spider Dysdera crocata.

 For a creature that evolved in water, you might wonder how they made the transition to land and were still able to breathe. Unlike mammals that evolved from fish that already had primitive lungs, isopods retained their gills when they evolved to live on land, breathing through trachea-like lungs in their paddle-shaped hind legs (pleopods), called pleopodal lungs. This means that they need a reasonably high humidity to keep their 'lungs' damp, but  Hemilepistus reaumuri thrives in the deserts of North Africa and the Middle East. They can survive in temperatures of up to 35°C and humidity as low as 6%.

Once isopods have grown they will find a mate, although some species breed through pathogenesis so the entire species can be made up of females, in others some females may have a group of males, or a pair may establish and defend a territory. Once they have mated the female will carry the eggs in a specialist pouch known as a marsupium.

 At some point, the eggs will hatch and she will be carrying fully formed miniature isopods. It's not completely clear why she will decide to release the babies, but some studies have shown that the mancae will decide when they're ready and somehow escape.