Do isopods lay eggs?

Yes, and also no, To answer this we need to have a wander through evolutionary biology to find out how isopods breed, how they both lay eggs and have live young.

Egg laying is one of the original forms of reproduction, more complex than just splitting in two, but less complex than carrying young and providing it with oxygen and nutrition directly via a placenta. However, there have been many evolutionary routes to live births. Many species retain the eggs until they hatch internally. There is no placenta that connects the young to the female. Marsupial mammals will give birth to tiny live young that then spend time in a pouch. Platypus lay eggs, and then nurse their babies. Seahorses deposit the eggs and sperm in a special pouch that the male holds, the young will hatch in the pouch and the male will expel them. Some toads gather their eggs on their back and allow skin to grow over them. Some fish gather their eggs in their mouths and hold on to them long after the fry have hatched, letting them out to forage and calling them back into their mouths at any sign of danger.

How do isopods breed?

 Isopods are partway along one of those evolutionary traits. Many marine species of crustacean expel eggs and sperm into the water, hoping that they will randomly encounter each other. The chances of them meeting are improved by the animals gathering in groups at breeding times.

Marine isopods have developed an even better method to ensure their eggs get fertilised, some females will take, hold and store the sperm from the male, then will put her eggs in a specially developed pouch, the marsupium, use the sperm to fertilise them, and then keep hold of them until almost fully formed miniature adults are allowed to escape. After this, the female normally has nothing more to do with them. Although there is so much we don't know about marine isopods.

Terrestrial isopods

 When isopods crawled out of the ocean, the marsupium was an adaption that allowed them to lay their eggs without having to retreat to the oceans to breed, as many other species of crustaceans do. Instead, they produce a fluid that goes into the pouch and protects the eggs from drying out. This means that terrestrial isopods need the humidity to be in the correct range to allow the females to incubate the eggs.  

Do isopods take care of their young?

Some species of isopods will release the young, known as manca, and then have no more interactions with them. But many of them do practise some form of parental care. Some species will build walls of their own dung and defend that territory, and any young in that area. Others are known to gather in groups and it's likely this gives the newly released manca some added protection. At this stage, the youngsters need to moult before they can grow their seventh pair of legs.

Breeding in your terrarium or vivarium.

 From the point of view of survival of the species, and for you if you’re hoping to breed your isopods, the living young are less susceptible to being a small snack for predators than eggs are, and there is a far lower risk for the eggs being attacked by fungus. But in general, it takes more energy for the female to carry the eggs till they hatch than if she just scattered the eggs.

The number of young the female can carry varies depending on her size, the larger she is the more young she can carry. This means that you may have to wait for your females to grow larger before you start to see lots of manca running around.

 Interestingly enough whilst generally isopods are either male or female, there are a variety of things, including a bacteria, that can turn males of some species into females. Most species have a ratio of one male to 2.5 females in terms of those born. This means that if everything is equal you should have plenty of females in each generation to carry things along.

 The fact that the female can store the sperm of previous males means that she may not be mating with the males that you see following her around or even clinging to her back waiting for his chance to pass on his genes. There is evidence that some vertebrate species can choose the most robust sperm for their offspring, although that hasn't been studied in isopods. There is a chance that even if you put two brightly coloured isopods together, that she is holding on to sperm from a previous mating. If you are breeding for specific traits then it's worth isolating the lines when the females are too young to breed and using them to continue the lines.

Isopods have a fascinating biology, if you liked this article follow us on Facebook and (insert links to Facebook and your other social media) to find out when we have a new article out.

If you want to have a try at breeding isopods for the first time, then Dairy Cows are probably your best bet to start with, although Porcellionides Isopods also can be rewarding to watch as the colony grows in size.