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Do Isopods Have Genders?

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Also known as roly-polies, doodlebugs, sowbugs, or pillbugs, isopods are not bugs. They are characterized by their antennae and seven pairs of legs. Isopods are terrestrial crustaceans who share the same family as lobsters and shrimps. 

Nowadays, it is a common thing to find breeders breeding these little creatures inside culture tanks. If you’re looking to breed them, you will want to find out if these creatures have genders at all and if they do, how to determine them. 

Do Isopods Have Genders?

Isopods do have genders.

However, it might not be an easy task determining the gender of each isopod till they reach maturity when their distinct features start to manifest.

For a start, a healthy isopod colony consists of ten or more individuals who on average, have a fair distribution of males and females.

In cases that you want to purchase more exotic types of isopods, this means that they will be more expensive and will probably be delivered in lower numbers, so you might need to insist on the balance of genders to avoid having a single-gender colony.

Now that we know isopods have genders, how do you distinguish the two?

Handling Isopods for Gender Evaluation

Isopods are very tiny and employ a defense mechanism of curling up into a ball whenever they feel threatened. Because of this, it can be a little difficult to handle them to determine their genders and you will need to be extra careful when handling them.

The best way to do this is to put them in a transparent enclosure that will enable you to see their undercarriages with the help of bright light.

If the isopod is large enough, you can lightly hold one between your fingertips to have a closer look at it, most preferably using a magnifying glass.

isopod crawling on the stone

Determining Gender of Isopods

Just like any other animal, isopods show distinct levels of sexual dimorphisms. Since they are small crustaceans, however, the differences might be slight and really difficult to tell.  When determining the gender of isopods, the most distinguishing feature is always visible on the underside.

On their undersides, you can tell the difference on their segment plates. The females have more distinctive rectangular shapes, while the males have pointed arches. 

On the other hand, some isopods have phenotypic sex determination features, which means that you can simply tell their gender difference by looking at their outer looks. Males, for example, are known to have a longer last pair of legs called uropods, while the females have leaf-like growths on their undercarriages, typically between the 1st and 5th legs called brooding pouches.

Males, on the other hand, possess special copulatory organs on their first two appendages. Under these last two appendages are a male organ called penile papillae, which will make their gender more clear if you bend it back to see it. Although this method is highly reliable, it could end up hurting or killing the innocent creature.

Some isopods can also be differentiated by the distinct markings in their crusts, like the female Porcellio silvestri, who has a shiny full bright orange color, while their male counterparts are rather plain in color. Their males, however, are bigger with distinct coloring and are generally more ornate.

Among other distinct features, adult male isopods also have slightly longer antennae as compared to the females, although they grow generally at the same rate and are comparatively equal through most of the development stages. 

With some other isopod breeds, females are generally wider and a little squatter while males are relatively thinner and longer compared to females. The female’s shape is responsible for providing more space for brooding pouches which are sacks they use to keep their young ones safe before they hatch.

The Brood Pouch

Also known as a marsupium, the brood pouch shows up as soon as the isopod hits puberty. At younger stages, the feature is only visible like a leaf beneath the first 5 pairs of legs.

After mating, the fertilized eggs are kept inside the brood pouch and its protective liquid for a couple of weeks till the younger ones are ready to hatch.

At times, as in the case of pillbugs, the brood pouch is the only feature that distinguishes the males from the females.

closeup photo of isopod under a twig

How Reliable is Isopod Sexing?

At younger stages, there is no specific way of telling apart the isopod genders, regarding the fact that even the males will maintain the female look till they hit adulthood when their uropods start to show up.

However, as soon as they hit puberty, they will start reproducing even if they are only half-grown.

How do Isopods Mate?

Isopods reproduce easily and in large numbers. Just before the mating season, you will see a lot of movement in the tank, where the males will constantly be following the females because they are naturally attracted to them. In this chase, the males will try as much as possible to get close to the females for a chance to mount upon them for them to effectively pass their gametes to the females. 

The males will typically sit on the females for hours, often tapping their uropods against the segmental plates on the lower end of the female isopod’s body.

However, if you keep both the male isopods and the females in one enclosure, uncontrolled mating could soon become a problem because these little creatures reproduce in large numbers, meaning you will soon run out of space for the ever-growing pack.

Before breeding them, therefore, you must find ample space to put them.

After fertilization, the fertilized eggs will wander up to the brood pouch where they will gradually develop and later emerge as mini-isopods after about 3 to 7 weeks.

Depending on their age, female isopods will carry between 10 – 160 fertilized eggs, with the younger ones harboring a lesser number compared to elder ones. For some isopod breeds, the females can have two successful breeding seasons in a year.

close up photo of brown isopod with white spots

Are Isopods Pets or Pests?

Although greatly misunderstood, isopods contribute to the well-being of a garden. Although they might eat vegetables, isopods assist in breaking down compost and any decaying matter, greatly helping in maintaining the soil health.

To keep them from eating your vegetables, ensure you provide them with enough monocotyledonous leaves such as grass, banana, and bamboo leaves. These are their favorite.

Other Fun Facts

  • Just like fish, isopods have gills for breathing and should be kept in a moist environment.
  • Isopods are protective of their young ones, and will often stay with them till they are mature enough to move out of the colony in search of new territories. However, even after moving out, the younger ones won’t wander too far away from the parent colony.
  • In Europe, most isopod breeds have spots of red making them resemble the black widow spider, a trait that helps them keep predators away.
  • Isopods have blue blood, evidenced by the turning of their body coloration to bright blue when they are sick.

Conclusion

Isopods are small crustaceans with remarkable abilities that help them in their defense mechanisms, breeding, and feeding.

Although you might be tempted to pick one up for closer inspection, remember that these creatures are very fragile, so you need to be careful when picking them up.

If you have quite a large colony, there are higher chances that the genders are equally distributed, making it unnecessary to find out their genders.

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