How Do Woodlice Lose and Absorb Water Through Their Cuticle?

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People who ask how do woodlice lose and absorb water through their cuticle are usually asking about a small animal that lives on land yet depends on moisture. The answer has two halves. The outer covering, called the cuticle, slows water loss, and in some woodlice species water can also enter as vapour from humid air. The two studies used here measure water loss in several species and track water uptake during molting. The explanation below stays with what those papers report, and each factual point is tied to a verbatim quote.

Quick answer

• The cuticle is the main barrier between the animal and its environment, and its outer epicuticle is important in limiting water loss.
• Terrestrial isopods lose water through the body surface, and the rate of loss depends on temperature and humidity.
• Some woodlice can absorb water vapour from air that is below full saturation, a process called active water vapour absorption.
• Water uptake is most visible around molting, when the animal gains mass before its old cuticle is shed.

The cuticle as the water barrier

The woodlouse body is covered by a hard outer layer. The desiccation paper states that “The sclerotized cuticle is the main barrier between oniscidean individuals and their environment.” That barrier is built in layers. The paper describes the outer covering as “The crustacean exoskeleton is composed of four layers: the epicuticle, the procuticle (exo- and endocuticle), and the membranous layer.”

The layer that matters most for water is the outermost part. The paper explains that “The epicuticular layer is important in inhibiting water loss.” It also divides this layer further: “It is divided into sublayers: the cement layer, the surface coat, the waxy layer, and the inner epicuticle.”

The molting paper describes the cuticle in broader terms. It says that “The cuticle of arthropods is an organ of extraordinary adaptive versatility,” and that it provides “extreme resistance to water loss from intrinsic or superficial lipids in many terrestrial taxa.” This explains why the outer layers are so important for land animals in dry air.

How woodlice lose water

Water leaves the body across the same surface. The desiccation paper explains that “It is well-known that terrestrial crustaceans lose water more rapidly than most other land arthropods due to their tegumental transpiration.” The same paper applies this point to the terrestrial isopods it studies. The cuticle slows the loss, but it does not stop it, and the rate of loss changes with the surroundings.

Environment matters a great deal. The paper states that “The rate of water loss is affected by the environmental temperature and humidity.” The desiccation paper states that “Water loss rate and mortality were studied in three different RH values in glass desiccators.” The paper notes that “The experimental setup did not allow air to circulate,” which means the water loss figures are a controlled measurement and not a field value.

Species differ. At the lowest humidity tested, the desiccation paper reports that “A. vulgare lost significantly less water than the other species.” Within the genus Armadillidium, the same paper says that “A. vulgare had the thickest tergal cuticle,” which lines up with its lower water loss in that comparison. The paper also says that “The specimens which died during the experiment lost significantly more water than the surviving ones,” so water loss was linked to survival in the test.

Why thickness and body size matter

The desiccation paper links water loss to the thickness of the outer covering. It reports a negative correlation between water loss and “the tergal cuticle thickness,” meaning thicker cuticle went with lower loss in its measurements. The same paper explains the general concept: “Humidity preference reflects a species’ capability for water retention which, in turn, depends on the integumental barrier.”

Body size also appears in the results. The paper says that the mass-specific water loss “showed negative correlation with the initial weight,” which means larger animals lost less water per unit of mass in these tests. Size and cuticle thickness are therefore both part of the picture, and the paper treats them as separate traits.

Water uptake from water vapour

Woodlice do not only lose water. The desiccation paper notes that “Nevertheless, terrestrial isopods can take up water directly,” and that they can also take up water “from water vapour,” which “allows rapid recovery of water loss.” That recovery matters after a dry spell, because the animal can rebuild its water balance without finding liquid water.

The molting paper goes further and studies a specific mechanism. It defines the process: “WVA is defined as any energy-dependent process allowing an animal to absorb water vapor from a vapor pressure below the equilibrium vapor pressure of the animal’s body fluids.” The word WVA stands for water vapor absorption, and the paper says it is “a potential mechanism for volume expansion in a few families of terrestrial arthropods.”

The paper reports that “This study shows for the first time that crinochete oniscideans utilize active water vapor absorption (WVA) to increase body mass prior to ecdysis.” The molting paper describes its setup this way: “Animals were maintained in controlled humidity.” It also reports that “in an RH >95 % animals can replenish significant water losses,” which indicates how much uptake can happen when the air is nearly saturated.

The same paper explains why this matters for land animals in particular. It says that “the oniscidean isopods are the only crustaceans that can live truly independently of liquid water.” Because they can live away from standing water, the ability to draw water from humid air is important to their survival.

Molting and water uptake

Molting is a time of change for the cuticle. The paper explains that “Following ecdysis, the pliant new cuticle is susceptible to buckling under gravity and requires elevated hydrostatic pressure for support.” Before the new layer hardens, the animal must expand its body. The paper notes that “Terrestrial species also require a mechanism of volume expansion and stretching of the integument prior to sclerotization.”

The molting study ties this expansion to water vapour. It reports that “Both species attained a mean water uptake” and that each “showed a progressive increase in mass from 5 days prior to ecdysis.” Here PE stands for posterior ecdysis, defined in the paper as “Posterior ecdysis (PE) – posterior cuticle shed.” The mass rise is followed by a “variable period of mass loss” after the molt.

The uptake did not continue through the whole molt. The paper suggests that “The cessation of WVA following the intramolt (between PE and AE) may be due to an inability to absorb water vapor during the period of new cuticle formation.” In plain terms, the new cuticle is being formed in this window, and water uptake from air stops during that time.

Comparing species

The molting study compares two species with a third, very different group. It says that “Both belong to the section Crinocheta,” which is the group that showed the water vapour uptake. The third species, which is “a non-crinochete oniscidean, Ligidium lapetum,” behaved differently. The paper reports that Ligidium lapetum “failed to show any mass gain” in the humid tests, which marks the uptake as a trait of the crinochete group in these experiments.

The desiccation study adds a further comparison across six species. It reports that “Protracheoniscus politus had the highest and A. vulgare had the lowest water loss.” That is why the answer to how do woodlice lose and absorb water through their cuticle is not the same for every species.

How we chose these sources

This article uses two open-access papers from PubMed Central. Both were fetched directly for this draft and both returned HTTP 200 with full article text. One paper compares water loss and cuticle thickness across species, and the other measures water uptake during molting. Between them they cover the barrier, the loss, the uptake and the molting link, which are the main parts of this question. Neither is a retail page, and neither recommends a product.

What we could not verify

What the sources do not say

Both papers describe controlled laboratory conditions. The desiccation study used sealed glass desiccators with no air movement, and the molting study used humidity chambers. The sources do not give field measurements of how much water a woodlouse loses in a garden on a given day, so this article makes no such claim.

The sources describe the cuticle layers in general terms. The paper says the epicuticle is important in limiting water loss, but it does not give a single value for how much each layer contributes, and this article does not add one.

The molting study tests a limited set of species. It says that “Both belong to the section Crinocheta,” and its conclusions apply to that group. The sources do not say how every woodlouse species handles water uptake, so the variation across all species remains open.

Frequently asked questions

Do woodlice drink water?

Not in the usual sense. The desiccation paper says that “terrestrial isopods can take up water directly,” and the molting paper notes that for many land arthropods “a dependable liquid water source is often not available.”

Why do woodlice lose water through their skin?

The desiccation paper explains that “It is well-known that terrestrial crustaceans lose water more rapidly than most other land arthropods due to their tegumental transpiration.” The cuticle slows this loss, but the body surface remains the route.

Can woodlice absorb water from humid air?

The molting paper reports that “This study shows for the first time that crinochete oniscideans utilize active water vapor absorption (WVA) to increase body mass prior to ecdysis.” The uptake is linked to the molt in these species.

Does a thicker cuticle help a woodlouse keep water?

The desiccation paper reports a negative correlation between water loss and “the tergal cuticle thickness,” which means thicker cuticle went with lower loss in its tests.

Do all woodlice species lose water at the same rate?

No. The desiccation paper states that “A. vulgare lost significantly less water than the other species,” so the rate differs by species. The paper also reports that the cuticle “thickness differed significantly interspecifically” within the genus.

For a related look at how a small animal survives a dry season by changing its body, read how do land snails survive hot dry summers by estivating. For how insects shed and rebuild their outer covering, see how do insects molt their exoskeleton.

Sources

• Morphological traits – desiccation resistance – habitat characteristics: a possible key for distribution in woodlice (Isopoda, Oniscidea). PubMed Central, https://pmc.ncbi.nlm.nih.gov/articles/PMC6288246/ (HTTP 200, opened 2026-10-28).
• Water vapor absorption allows for volume expansion during molting in Armadillidium vulgare and Porcellio dilatatus (Crustacea, Isopoda, Oniscidea). PubMed Central, https://pmc.ncbi.nlm.nih.gov/articles/PMC6288263/ (HTTP 200, opened 2026-10-28).