Can Isopods Drown? What Every Keeper Needs to Know
It sounds like a trick question. Isopods have gills, they're crustaceans related to lobsters and crabs, and they evolved from marine ancestors. Surely they can handle a bit of water? Well, not quite. The short answer is yes – terrestrial isopods can and do drown. It's something that catches many new keepers off guard, and it's a real concern if you're running a bioactive setup with water features or keeping your pods alongside amphibians.
If you've ever found a few of your isopods floating lifeless in a water dish, you're not alone. This happens more often than you'd think, and it comes down to a quirk of their biology that's worth knowing about.
Wait, Don't They Have Gills?
They do. Terrestrial isopods still carry the gills their aquatic ancestors used millions of years ago. These gill-like structures are called pleopods, and they're located on the underside of their abdomen. But here's the catch – the gills of land-dwelling isopods have adapted for a very different purpose than those of their ocean-living cousins.
The pleopods of terrestrial isopods work by absorbing oxygen from a thin film of moisture on their surface. They've evolved to function in damp air rather than underwater. Think of it like this: they need humidity to breathe, but submerging them is like asking you to breathe through a soaking wet cloth pressed against your face. The system just wasn't built for that.
Some species, like the Armadillidium genus, have even developed structures called pseudotracheae that work somewhat like primitive lungs. These allow them to extract oxygen from air more efficiently, but they're hopeless when fully submerged in water.
Why Do Isopods Drown?
When a terrestrial isopod falls into water, it faces a few problems at once:
Their gills can't process submerged oxygen efficiently. The thin membrane on their pleopods is designed for gas exchange with humid air, not for filtering oxygen out of water like a fish's gills would. Once underwater, they simply can't extract enough oxygen to survive.
They can't climb smooth, wet surfaces. If an isopod tumbles into a water dish with vertical sides, it often has no way to grip the surface and pull itself out. Their legs are built for gripping soil, bark, and leaf litter – not slick plastic or glass.
Exhaustion sets in quickly. Isopods aren't swimmers. They'll paddle around desperately trying to find an exit point, and if they don't find one within a few minutes, they'll exhaust themselves and drown.
According to keepers who've observed this behaviour, some isopods can drown in less than a minute if they can't find a foothold. Others might struggle for several minutes before giving up. Either way, it's not a pleasant end for these little creatures.
The Paludarium Problem
If you're keeping isopods in a vivarium or bioactive enclosure alongside reptiles or amphibians, you've probably got some kind of water feature. This creates a challenge: your pet needs water, but your isopod cleanup crew can fall in and drown.
Some keepers report finding drowned isopods in their water dishes every few days. It's frustrating, especially when you've invested in a nice colony of something like Cubaris or Porcellio species.
Part of the issue is that isopods are naturally drawn towards moisture. They need it to breathe, after all. So a water dish looks appealing to them – right up until they fall in and can't get out. Scientists have noted that isopods haven't fully "completed" their evolutionary transition from sea to land. Their instincts don't always steer them away from water the way you might expect.
How to Prevent Your Isopods From Drowning
The good news is there are several straightforward ways to reduce or prevent isopod drownings in your enclosure.
Add Escape Routes to Water Dishes
The simplest fix is to give isopods something to climb on if they fall in. Try adding:
- Small stones or pebbles that break the water's surface
- Pieces of cork bark floating in the dish
- Natural lump charcoal (the kind without lighter fluid) sticking out of the water
- A small stick or twig leaning against the edge
The key is making sure there's something with texture that an isopod can grip and climb. Smooth stones won't cut it – they need rough surfaces their legs can latch onto.
Use Shallow Dishes
A deeper dish means more distance for an isopod to swim before reaching the edge. Keep your water dishes as shallow as practical. Some keepers use bottle caps or very low-profile dishes that an isopod could reasonably crawl out of on its own.
Consider Water Crystals Instead
Water crystals (also called water gel beads or hydrogel) are a popular alternative to open water dishes. These provide hydration without the drowning risk. Isopods can drink from them, and there's no open pool of water for them to fall into. Many keepers who house isopods with roaches or other invertebrates use this method exclusively.
Choose Your Species Wisely
Some isopod species seem more prone to drowning than others. Smaller species and those that are highly active or exploratory tend to get into trouble more often. Larger, more cautious species like Giant Orange isopods or the burrowing Rubber Ducky types may be less likely to wander into water features.
If you're setting up a paludarium with significant water content, dwarf species like White Shark isopods might struggle more than hardier options.
Create a Moisture Gradient
If your enclosure has areas with high humidity, isopods are less likely to seek out open water sources. They're looking for moisture, and if they can find it in the substrate or under moss, they won't need to venture near the water dish. Misting regularly and maintaining proper substrate moisture can help with this.
For guidance on proper humidity levels, check out our article on beginner isopod keeping.
What About Springtails?
If you're running a bioactive setup, you might be wondering about springtails. Unlike isopods, springtails are actually quite comfortable around water. They can float on the surface tension and often congregate on top of water features. You'll see them bobbing around happily while isopods would be in serious trouble.
This makes springtails a better choice for the wetter parts of a paludarium, while isopods handle the drier terrestrial zones. Many keepers run both species together – the springtails tackle mould and the wettest areas, while isopods process leaf litter and other organic matter in drier spots.
Can Any Isopods Survive Underwater?
Marine isopods and freshwater species like Asellus aquaticus (the water slater) are fully aquatic and breathe underwater without any problems. But these aren't the isopods you'll be keeping as pets or using in bioactive setups. The aquatic isopod article covers these fascinating creatures in more detail.
Terrestrial species – the woodlice, pillbugs, and the colourful species we sell – are all land dwellers. They've spent millions of years adapting to life on land, and going back into water just isn't something their bodies can handle anymore. It's a bit ironic, really. Their evolutionary history started in the ocean, but there's no going back now.
Signs Your Enclosure Might Be Too Wet
While isopods need humidity, there's a difference between damp substrate and soggy conditions. If your enclosure is waterlogged, you'll start seeing problems beyond just drowning:
- Isopods clustering at the highest, driest points in the enclosure
- Visible standing water in the substrate
- Mould growing faster than your cleanup crew can handle
- Isopods attempting to climb the walls excessively
- Health issues like failed moults becoming more common
If you're seeing these signs, ease off on the misting and improve ventilation. Your isopods need moisture, but they also need areas where they can escape to drier ground when they want to.
The Bottom Line
Yes, isopods can drown, and it happens more often than new keepers realise. Their gills are designed for humid air, not submersion, and their legs can't grip smooth wet surfaces to escape. But with a few simple precautions – escape routes in water dishes, shallow containers, and proper humidity management – you can keep your colony safe while still providing water features for other inhabitants.
If you're just starting out with isopods, it's worth picking beginner-friendly species that are hardy and adaptable while you learn the ropes. And if you're designing a bioactive setup with water elements, plan your layout so that isopods have easy access to drier zones and can avoid the deep end entirely.
Have questions about setting up your enclosure? Feel free to get in touch – we're always happy to help.
