Humidity Guide

From Ant Keeping Wiki


Why is Humidity Important for Ant Keeping?

Ants need a certain degree of moisture, in particular their brood which is usually most sensitive. If the nest is too dry the ants and their brood may dry out and die or new workers may eclose crippled and dysfunctional.

It is important to know the rough humidity preference of your ants – some ants like Myrmica sp require a very moist nest while other ants, many Camponotus species in particular, prefer dryer nests and might even move into the outworld if their nest gets too moist.

To fully understand humidity and it's effect on ants we need to establish a few basic things first though.

What is Humidity?

Humidity is a measure for the amount water vapor in the air. Humidity is relative value with 100% being the maximal amount of water air can hold at a given temperature.

Warm air can hold more water vapor than cold air - hot air at 40°C with a 60% humidity actually contains multiple times the amount of water vapor than cold air at -30°C with a 90% humidity (remember, it's a relative value) - which has important implications as described in the following chapters.


What happens if the humidity reaches 100%? Well, this is basically the point where the air cannot hold anymore water vapor and the water starts to condensate (= transition to a liquid state) at any available surface – in the outside world this will result in dew and fog.

(Fog happens when water vapor condensates on dust particles in the air - this can be used for quite spectacular show effects: As long as there are no dust particles in the air no condensation can happen, so it is possible to keep over-saturated yet transparent filtrated air inside a chamber - but when dust is blown into the chamber it will result in instant fog.)

Since warm air can hold much more water vapor than cold air fog often develops during the early morning hours when the sun starts to heat up the ground (and evaporates the water in the wet earth) but the air is still cold - trees can dramatically increase this effect as trees use their leaves or needles to pump enormous amounts of water into the surrounding air. As the sun rises further the air temperature increases and so does the amount of water vapor the air can carry – the fog disappears.

Condensation Inside the Nest

Condensation in ant keeping mostly happens in very wet heated nests – the heat causes the water to evaporate which then condensates on the cooler nest surfaces, particularly on the lid or the upside of a test tube.

Though sometimes unavoidable moisture can pose a real threat to the ants. Larger drops can quickly become death traps for smaller ants (they get sucked in by the surface tension and drown) - this can even happen to big ants like Camponotus nanitics. In extreme cases condensation can lead to the flooding of an entire test tube wiping out the colony in the process.

One of the easiest methods to stop (or at least greatly reduce) condensation is to simply stop heating the nest, so that the temperature inside the nest and the room temperature become equal. This not only reduces the evaporation rate of the water from the tank but also stops water from condensating solely on the lid as the lid is no longer cooler than any other parts of the nest (most condensation will still happen on the lid as the water vapor naturally rises upwards but it will disperse at least a slightly better across other nest surfaces).

Condensation in an outworld can be reduced by simply keeping the lid open. The increased ventilation carries out most of the water vapor (unless your room humidity is already at almost 100% like in some tropical countries).

Different Ants Need Different Humidity Levels

Moist nests are generally more prone to mold and mite outbreaks, especially when the ants decide to store food or garbage inside the nest. Moisture-loving ants usually have methods to deal with these issues but sometimes an ant keeper needs intervene and remove trash from the nest.

For beginners it's probably best to start with an ant species that is relatively dry-resistant like Camponotus carpenter ants, Messor/Pogonomyrmex harvester ants , Formica wood ants, Lasius garden ants or Temnothorax acorn ants. Their nests can be kept at a fairly low humidity level (the nest of Temnothorax and some Camponotus species do not need to be watered at all) which avoids most problems with condensation, mold and mites.

Some ants that nest in dry places are incredibly dry-resisant, studies have shown that Camponotus pennsylvanicus brood only starts to show deformations at 20% humidity and below – which is way less than the average room will ever have (very heavily air-conditioned rooms may reach this level but usually it's unpleasant for humans, too).

Moisture-loving species like Ponera or Myrmica can either be regularly sprayed by a humidifier or kept in a naturalistic setup. If you want to keep an ant that requires high humidity levels in a Ytong nest you should put the stone into a shallow basin filled with water so the stone is always moist (this works well with Myrmica).

Hydration Gradient – Listen to Your Ants

Having a hydration gradient in a nest is always a great idea. If you keep one side of the nest moist and the other dry the ants can choose freely where they want to nest and will congregate on the most preferable spot. By watching your ants you can easily find out what their preferences are in case you're not sure about that. If the nest is too dry the ants will all huddle up along the side where the nest gets hydrated or may even move into the water feeder if possible. If the nest is too moist the ants will move to the opposite side or even abandon the nest altogether and nest somewhere in the outworld.

Vertical Ant Farms and Leafcutter Cylinders

Vertical nests should ALWAYS have a drainage bottom layer of larger pebbles and a port to remove excess water. If you accidentally over water your nest, end up with water standing at the bottom of the nest and have no way to remove it that's a really really really bad thing. Standing water is a perfect breeding ground for germs of all sorts.

The same goes for leafcutters. Most leafcutter ants require a constant humidity level of almost 100% which quickly leads to water gathering at the bottom of the cylinder. The bacteria growing in that excess water can quickly infect and kill off large portions of the fungus which usually leads to the ants dying as well.

Harvester Ants

Harvester ants (ants that use seeds and nuts as their primary food sources) are a bit of a special case in that they need a moist nest part (not too moist but still some low-level watering) for their brood and a dry nest part (preferably bone dry) so the seeds and nuts they store don't mold or germinate.

At the test tube stage this isn't too much of an issue as they usually store their seeds in front of their nest entrance and only drag the ones they process into the tube, although it may be a good idea to offer them a second tube without a water chamber when the colony grows beyond a dozen workers.

Large colonies can either be kept in a nest with a hydration gradient or in nest packs of two (like two farms in a chain) with one being kept moist and the other kept dry.

Naturalistic setups

Soil setups with plants are quite easy to water – you can just spray them with a water duster bottle for plants every few days. In case you water in a more traditional way it's probably best not to just spill water across the entire tank but leave out a few places so the ants can move to dryer parts of the setup when their nest gets flooded. If you want to increase the soil's ability to store water you can add perlite or something similar to the soil (it is obviously best to do this when creating the tank, not when the plants and ants are already in there).

On Hygrometers

Hygrometers are devices that measure humidity and can be useful tools but they're not required for most ants. Also note that a hygrometer mounted at the upper side of the tank doesn't even remotely measure the humidity levels in the soil or the nest. To get an actual solid result you need to stick the hygrometer into the soil (better even bury the sensor) or the nest. And be aware that certain small ants like Temnothorax love to nest in hygrometers.

Backup Water Tube

Most ants can survive without food for several weeks but some won't even make it through a single day without access to water. It is always a good idea to keep at least one water tube somewhere in the setup, either directly attached to the nest or in the outworld. Not only allows this the adult ants to survive should you forget or be unable to water the nest, it can also act as a humid backup nest to prevent the sensitive brood from drying out and dying.

Hibernation and Humidity

Hibernation is a critical time for all ants, especially those from temperate and cold region as they become completely immobile and reliant on favorable environmental conditions for their survival.

Under most conditions the evaporation of water in cold environments is very low as the air cannot hold much water vapor, so the water tends to say where it is (in the soil of an ant farm or the water tank of a test tube). There is however one notable exception and that is if you keep your ants in the fridge. Gas-compression refrigerators have a very drying effect on anything inside them, they are literally sucking the water out if things. This isn't too much of an issue with a closed test tube where the front cotton plug not only prevents water from evaporating but also keeps humidity levels inside the test tube very high, however it's really a big problem with nests made from acrylic, ytong, gypsum and similar materials. A possible solution is to put the entire nest into a (preferably tightly fitting) styrofoam box, this has the same effect as the front cotton plug of a test tube. It's probably still best to carefully water them once a month though. Some ants can also be put into a styrofoam box and hibernated outside on the balcony or in the garden – northern Camponotus and Temnothorax species can survive up to -30°C. Just make sure they're safe from rain and curious animals. Note that during cold peaks their test tubes can actually crack or break but this isn't an issue until temperatures rise above 0°C again – best put some absorbent mold-resistant material (like perlite) at the bottom of the box to absorb the water, just in case. This prevents the ants from drowning and keeps humidity levels decent even if the test tubes fail.

A bit of condensation will always happen when you put a tube into the cold but as long as it doesn't flood the tube it's not a problem. You can prevent condensation by cooling down the tube very slowly over a duration of several days - that way you will get very little gradual condensation which might be able to exit the tube through the cotton before it gets too much.

A big issue with hibernation of ants in test tubes that is often overlooked until disaster happens is the expansion of water during their wake-up period. Water has it's highest volume at +4°C which means that at this temperature water is taking up the least space per weight – it cannot compress any further (ice actually has less density and takes up more space than cold water, this is why icebergs can swim on the ocean water and why bottles burst when their contents freeze). Due to the water expanding as the temperatures rise it is possible that the test tube gets flooded and the ants drowned.

This is most likely to happen when a test tube is brought from a very cold environment (fridge at 5°C) directly into a very warm environment (living room at 25°C) – the water expands so quickly that it has no chance to push the cotton plug forward, instead the water simply gets pushed through the cotton and leaks into the ants' living quarters. While such a flooding is an obvious problem for small ants it is actually of equally threatening to large ants like Camponotus where a queen can take up to two weeks in a warm environment before she is able to move again.

Test tubes should be regularly checked during the post-hibernation period and kept at a slight angle so the water stays at the back of the tube even if a leak occurs (this obviously may not work if all the ants are sitting directly on the cotton and get flooded anyway). In the worst case you can just break the water tank on purpose (put a towel below the tube before doing this so you don't end up with a lot of glass shards and ants swimming in a pond on your table) and carefully drop the still paralyzed ants into a fresh tube.

Bonus Tip: If you check on your ants during hibernation make it as fast as you can. As soon as the temperature inside the tube starts to rise, water will evaporate from the water tank and when you put the tube back in you get condensation because the air cools down and can no longer hold the water it just draw. This gets worse the higher the temperature inside the tube rose during your check.

Humidity and escape barriers

Let's just put it straight and simple – barriers and moisture don't work well together.

Most (if not all) common barriers used in ant keeping rapidly degrade under high humidity conditions.

There are some barriers that are more resistant to moisture than others, like paraffin - but those don't work for all ants (Formica species in particular have a nasty habit of sticking debris onto paraffin barriers rendering them useless very quickly).

This doesn't necessarily mean that barriers like powder of Fluon don't work at all in humid environments but they have to be replaced very frequently (like every few weeks) and you need to be extra vigilant about large ant groups congregating close to the barrier. Condensation can wreck powder barriers within minutes and should be avoided if possible.


Managing humidity isn't that hard and can be done very well with some basic knowledge. The main issue for new ant keepers is that we as humans are barely affected by it and tend to forget what a large deal this is for a lot of ant species, especially the smaller ones. Many cases of ants not laying eggs, workers dying or ants emerging from their cocoons crippled can be traced down to a lack of humidity.

As such basic knowledge about humidity is important and needs to be spread, especially to people who are new to ant keeping, so they can raise their first colonies successfully and add to our great communities surrounding these wonderful and amazing social insects.

Crash Course in Biology: How Ants Breathe

Ants don't have lungs like we do, instead they have tiny openings in their sides called spiracles, usually one pair per segment. These spiracles expand into a vast network of tubes called Tracheae running through their entire body. Ants also do not breath but rely on passive air circulation - this system works the more efficient the higher the environment temperature is as passive air movement (the movement speed of individual air molecules) is faster at higher temperatures.

But there is a another thing that limits the capabilities of this system and ants in general – humidity. Water evaporation and overheating is a huge deal for ants and hot surface temperatures can make it impossible for them to leave their nest without being cooked alive. Not surprisingly foraging activity for almost all ant species is at it's peak when humidity is high, usually after rainfall. This is also the reason many ants are nocturnal and forage mostly at night, despite the lower temperatures. Prenolepis imparis, the “winter ant” even switches between foraging in the daylight during the moist spring and fall seasons and foraging at night during the dry Summer.

In past times, specifically in the carbon age, when the Earth was essentially a massive moist greenhouse land-based arthropods could reach enormous proportions – there were dragonflies with a wingspan of almost a meter and centipedes that grew several meters long. Today as the Earth is much colder and less humid the size of all insects is severely limited by their respiratory system design and only spiders are capable of rising above those limitations due to their vastly more advanced lunges. However with rising global temperatures the arthropods soon may very well find themselves on the verge of a new golden age (that is if our extensive use of pesticides doesn't kill them all first).