Is the Skin of Chamaeleo namaquensis Really Hygroscopic or Not?

The Namaqua chameleon 

(Chamaeleo namaquensis) is a ground-dwelling chameleon species found in the arid regions of Namibia, South Africa, and southern Angola. It inhabits arid and semi-arid areas, such as Karoo shrubland, sandy deserts, and gravel plains. It is particularly common in the Namib Desert and can be found as far south as Sutherland in the Western Cape, South Africa, and as far north as southern Angola. In eastern Namibia, its range overlaps with the flap-necked chameleon, Chamaeleo dilepis.

It is one of the largest chameleons in southern Africa, reaching up to 25 cm in length. Females are larger than males, which have proportionately more robust bodies, larger heads, and head ornamentation, as well as a bulge under the tail base due to the presence of hemipenes.

Adapted to a terrestrial lifestyle, the Namaqua chameleon has a shorter tail compared to arboreal chameleons, large dorsal spines, and a prominent, pointed casque. It has nasal salt glands that excrete excess minerals like sodium chloride and potassium. The chameleon can change color for thermoregulation, becoming black in the cooler morning to absorb heat and lighter gray during the heat of the day to reflect light.

This species is diurnal and primarily insectivorous, feeding on a variety of insects. It is known for its ambush predation strategy, using its long, extendable tongue to capture prey. The Namaqua chameleon is well-adapted to high environmental temperatures but can also tolerate periods of low temperatures.

Hygroscopic Skin Myth

In many sources, we read: "One of the most notable features of Chamaeleo namaquensis is its hygroscopic skin, which allows it to absorb moisture from its surroundings through capillary action. This adaptation is crucial for survival in its arid habitat."

However, chameleon skin is generally impenetrable to water. While there are some indications it can participate in minute water loss through the skin, it is generally not penetrable from the outside to the inside (C.R. Anderson, pers. comm.; own observations). It would be very strange if one species within a not too diversified genus (or even family) would possess skin with completely diverging characteristics. Therefore, it is essential to examine this claim in greater detail.

What is the meaning of the term "Hygroscopic"?

The term hygroscopic refers to the ability of a substance to absorb moisture from the air or its surroundings. Hygroscopic materials can attract and hold water molecules, often resulting in changes in their physical properties, such as swelling or dissolving. This characteristic is observed in various materials, including salts, sugars, and certain polymers. In the context of living organisms, hygroscopic properties can help them manage moisture levels and survive in arid environments by absorbing water from the surrounding environment, particularly from the atmosphere.

Applying the term "hygroscopic" to skin implies that the skin would take water from the environment, particularly from the atmosphere, and channel it through itself into the body. This, however, DOES NOT HAPPEN.

Origin of the confusion

In 1973, B.R. Burrage published a phenomenal work:

Burrage, B. R. (1973). Comparative Ecology and Behavior of Chamaeleo namaquensis and Chamaeleo pumilus. Annals of the South African Museum, 61, 1-158.

This study was submitted as a thesis in partial requirement of the degree of Doctor of Philosophy at the University of Stellenbosch, January 1972. It analyzes the ecology and behavior of Chamaeleo namaquensis in deep detail and until now, it is the most complete analysis of these aspects of any species of chameleons.

It is therefore clear, that the term "hygroscopic" is not to be taken strictly by definition, but rather refers to the function of the skin to channel the water in a way that it can be drunk... The water does not penetrate the skin. This would be a big disadvantage in the desert environment, as it must prevent water loss, which it efficiently does (as demonstrated in the same work on pages 90-93). It has been then cited and further elaborated e.g. by Robinson (1976) and Robinson & Hughes (1978) and cited as hygroscopy by many, even Wikipedia.

The described behavior rather refers to Rain-Harvesting Behavior called "Rain-Drinking" as postulated e.g. by Vesely and Modry (2002), than to real skin hygroscopy.

The skin of Chamaeleo namaquensis is NOT HYGROSCOPIC in strict sense, it leads by capilary action the water, appeared on its surface to places, where it can be utilized for drinking, but the water does NOT PENETRATE THE SKIN.

Burrage, B. R. (1973) Comparative Ecology and Behavior of Chamaeleo namaquensis and Chamaeleo pumilus. Annals of the South African Museum, 61, 1-158.