Moisture Gradient
What is a moisture gradient? This is a term synonymous with isopod keeping. It's one of the most vital components in your set up you need to keep maintained best as possible to ensure your isopods thrive. So lets break this potentially mysterious term down as it translates to everyday application and best practices.
A moisture gradient in terms of isopods mostly applies to the substrate. When properly set up, this means one portion of your enclosure has adequate moisture and humidity levels, while another part will have less moisture and humidity. This is what keepers are referring to when you hear the phrases "moist side and or dry side". With few exceptions, the bulk majority of isopods benefit by having a moisture gradient.
Why is this aspect so important? Isopods are crustaceans. Not insects, arachnids or any other invertebrate. The have external gills for respiration and the moisture content of the substrate and the air just above it dictate their ability extract oxygen from their environments. By providing a gradient, you allow them to self regulate their biological needs by having the option to move to different locations within the enclosure. The same concept with reptiles using thermo-regulation. They have a heat bulb they can bask under to warm up, or move to a different area to cool off if they get too hot.
Isopods can get oversaturated and essentially drown if the substrate and humidity is excessive high. Conversely they will quickly desiccate and perish if things get too dry. Having a well set up moisture gradient prevents either scenario.
So how do we set up a proper moisture gradient? Take a look at the image below.
An easy and effective method is build up one side of your enclosure with more substrate creating a natural slope where it levels off around the middle and keeps the same depth through the remaining length. The deeper side will naturally retain moisture longer than the shallower middle and opposite end sections. Adding other components like concave cork bark pieces, moistened sphagnum moss, layered leaf litter and similar will also aid in keeping the moisture from bleeding off too fast.
This is where things can get potentially tricky. There is no "one size fits all" answer outside of the sloping method in terms of how do I maintain the right moisture gradient after it's been set up. There are numerous variables. Some you can control and some you can't. Your job as a good keeper is to evaluate each and every one of these aspects and put the work in to determine what kind and how much fine tuning you need to employ to get your terrarium environment dialed in to stay consistent.
To determine that we have to look at the specific factors that affect moisture inside of the terrarium. Here are the most common variables and how to dial them in for your specific set up. We'll break this into two sections. Aspects you can control vs aspects you cannot.
Variables within your control
-Substrate depth: Your deep substrate side should be deep enough to hold moisture more than a nominal amount of time. You don't have to fill one side nearly full, but a minimum of 4 to 6 inches is usually sufficient on the moist side to keep things from drying out.
-Watering frequency: How much water you add inversely affects how long the moisture will be present. Do avoid just dumping large amounts of water in your enclosure. This can quickly drown your pods. Especially small babies (Mancae). A good isopod friendly soil moisture level means it has enough moisture you can see and feel, but isn't saturated to the point that if you grabbed a handful and squeezed you'd have large amounts of water dripping out between your fingers.
-Ventilation: With very few exceptions all isopods need some level of airflow. Ventilation needs will vary by species. Some require high air circulation while others require very little. While ventilation is essential, it also works against your moisture and humidity stability. Finding the right balance will vary by your enclosure type and the means of which ventilation is delivered.
The following two images represent different methods of providing ventilation for two different enclosure types.
If you're using a typical sterilite or plastic storage container, an air vent is the most common and practical option. Vents come in different sizes and you can add 1 or more to accommodate whatever your set up requires for moisture homeostasis.
If you are using any type of glass tank. Ideally with a screen lid, you can buy a sheet of polycarbonate and cut it to fit using aquarium safe sealant. You can either pre-drill some ventilation holes an/or cut the length slightly short so there's a gap to allow fresh air to circulate inside of the enclosure. Please note, polycarbonate is best for this use. Acrylic will warp and bend under high humidity.
Variables You Cannot Control
-Your local climate: Where you live has some influence on your enclosure parameters. For example the southwest part of the country is largely arid and dry. The southern states along the gulf and half of the eastern seaboard are mostly humid and warm. Since you cannot control global climates, the closest option you can meter is the inside of your home. Especially if your pods are in a dedicated room. Space heaters, humidifiers, your home HVAC settings and other such tools put some control back in your hands to be able to provide a safe and consistent climate for your isopods. Observe the trends inside of your enclosure and fine tune as needed.
Useful Tools for Managing Moisture Gradient
-Podwicks: These little devices are among the most useful enclosure components in the isopod hobby. There are different varieties, but all work on the same concept. Delivering a safe means of soil hydration without the risk of drowning your isopods with direct potentially harsh overhead watering. They also have a nice adjustable air vent that gives you a deeper level of control by being able to change the rate of airflow into your enclosure. Visit their website to see their outstanding selection.
-Govee Thermometer/Hygrometers: Govee's line of thermometer/hygrometers add a high tech touch while giving you direct insight on the current real time time conditions inside of your terrarium. It's important to note, these devices only measure the air temperature and humidity, but this still provides a valuable baseline on parameters which can alert you to potential disasters before they happen. Visit their website or look them up on Amazon.