Desert Monitor

Varanus griseus

Conservation status: Least Concern

Population trend: Decreasing

As the largest lizard in Morocco, the desert monitor is one of the most impressive reptiles in the country. As an apex predator, it plays a crucial role in maintaining ecological balance by regulating populations of small mammals, birds, and insects. However, the species faces numerous threats. From human persecution fueled by fear, tradition, and misunderstanding to the slow death suffered when trapped in water retention reservoirs, the desert monitor serves as a charismatic example of the delicate balance between desert wildlife and human activity.

The Desert monitor (Varanus griseus) is the largest Saharan lizard and belongs to the family Varanidae. It has an elongated, robust body that can reach more than one meter in total length depending on the population. The tail generally represents 120 to 150% of the snout-to-vent length1. The limbs of this monitor are broad and sturdy. Its size varies greatly depending on the region: in Iraq, some individuals reach 120 cm, while in Palestine specimens rarely exceed 100 cm, and in Algeria individuals measuring 80 cm are already considered large1. This variability suggests that climatic conditions and the availability of food resources directly influence growth and maximum attainable size. One may assume that Moroccan populations follow the same trend. During our expeditions, we observed specimens with a total length exceeding 80 cm.

Desert monitor (Varanus griseus) in a relaxed and non-defensive posture.

Desert monitor (Varanus griseus) in a defensive posture, using its tail as a whip and inflating its throat.

The coloration of the desert monitor is highly variable: in arid and sandy areas, some individuals display a uniform color, whereas in more vegetated environments, the patterning is more contrasted. Juveniles always show brighter coloration than adults1. Despite these variations, the base color is generally sandy interspersed with black patterns in bands of varying width, fine lines, or spots.

Headshot of a Desert monitor (Varanus griseus); note the nostrils positioned close to the eyes.

Headshot of a defensive Desert monitor (Varanus griseus) with its throat inflated.

It is noteworthy that the nostrils of the desert monitor are oriented backward and positioned close to the eyes. This likely indicates increased adaptation to dry and sandy environments.

This lizard is easily distinguishable from other saurian species found in Morocco, being the largest of them all.

In Morocco, Varanus griseus is widely distributed in desert and Saharan areas south of the Atlas Mountains, with a strong presence in the Atlantic Sahara4. Moroccan populations are probably all connected, even though this species is often considered to occur at low density in the country. The reality is certainly more complex, and some regions likely harbor higher densities of monitors. This impression of low density is probably due to its highly discreet behavior. Based on our observations and collected testimonies, it appears to be present in most regions south of the Atlas. However, it seems to be absent from the littoral region and the Souss valley.

On a global scale, its distribution range covers North Africa (Morocco, Mauritania, Algeria, Tunisia, Libya, Egypt, Sudan, Chad), the Arabian Peninsula (Saudi Arabia, Yemen, Oman, Kuwait), Southern Iraq and South-western Iran1.

Distribution map of Varanus griseus in Morocco

Distribution of Varanus griseus in Morocco, widespread throughout the arid landscape south of the Atlas Mountains.

The species occupies desert and semi-desert environments, including dunes, regs, rocky plains, and sparsely shrub-covered areas. It tolerates a wide variety of substrates (gravel, dunes, dry plains) and altitudes (up to 1200 m in Israel)1. During our expeditions, we found tracks and living or dead specimens within sandy deserts, low-density agricultural areas, relatively close to urbanized areas, and rocky-soiled plateaus with few inhabitants. This variety clearly illustrates the versatility of the species, far from the cliché of a purely desert-dwelling and elusive animal, and closer to that of a discreet opportunist.

Desert monitor (Varanus griseus) rescued from a well where it was trapped, showing its habitat

Desert monitor (Varanus griseus) rescued from a well where it was trapped for a long time - hence its sadly skinny appearance - in its habitat, near Smara.

Desert monitor habitat around Merzouga, with sand dunes, small bushes, and rocky formations surrounding the area.

Desert monitor habitat around Assa, sandy terrain with scattered acacias.

The desert monitor is adapted to extreme heat and dryness. Burrows play a crucial role: in Israel, they measure on average 125 cm in length and 30 cm in depth11. In Algeria, burrows exceeding 3 m have been described1. In Morocco, neither the depth nor the complexity of burrows is documented, but the sandy and rocky substrates make similar shelters plausible. These burrows allow the animal to access a cooler and more humid microhabitat.

The species actively regulates its body temperature. In Egypt, radiotelemetry studies show an optimal temperature between 35 and 38 °C, reached through direct sun exposure in the morning and then maintained actively until early afternoon37. The inactivity threshold is observed below 20 °C, and hibernation begins around 17 °C. The maximum tolerance is between 44 to 47 °C, beyond which mortality occurs7.

The desert monitor is active mainly in spring and autumn, while it likely remains confined to its burrows during the coldest periods of winter and the hottest periods of summer. In Algeria, two main activity periods have been described: from April to June, then in October1. In Mauritania, individuals have been observed until November1. In Morocco, we recorded several fresh tracks in multiple regions during August and September, indicating summer activity as well. Monitors have also been observed by other herpetological groups in Morocco in the middle of summer. It is therefore likely that monitors reduce their activity to the cooler hours of the day during the peak of summer, yet they still remain active.

In Algeria, monitor territories extend over 1–5 km², with daily movements reaching up to 8 km1213. These values may vary greatly depending on prey availability within the habitat.

The diet of the desert monitor is highly varied and opportunistic. In Israel, it mainly consumes other reptiles (lizards, snakes), ground-nesting birds, tortoises and their eggs, as well as mammals such as gerbils and young hares. It is also necrophagous, feeding on carcasses, including those of hedgehogs or even cats1.

Analyses conducted in various countries (Algeria, Turkey, Arabia, Egypt, Tunisia) confirm the same trend: the desert monitor devours any suitably sized prey it encounters, including invertebrates such as beetles, orthopterans, scorpions, and ants1. It is reasonable to assume that the Moroccan diet is similar, given the available fauna. Cases of monitors consuming horned vipers are reported verbally.

Data on reproduction in Morocco are lacking. However, in neighboring regions (Algeria, Tunisia, Israel), mating occurs in May and June, and egg-laying takes place in June–July611. Females can lose up to 47% of their body mass after laying11. Incubation likely lasts several months, and juveniles appear the following spring, although the exact duration of incubation remains uncertain1.

Traditionally, Varanus griseus is feared by Saharan communities, often considered venomous and associated with negative beliefs1. Although it does not possess venom comparable to that of snakes, a recent study on Varanus griseus caspius in Central Asia documented toxic effects linked to the saliva: generalized muscle pain, digestive issues, tachycardia, and bodily weakness, appearing after a prolonged bite during which the monitor remains attached for several minutes. A short bite carries no apparent risk9. Historically, the species has been persecuted in several countries where it is associated with negative beliefs1.

In Morocco, we found no evidence of active hunting targeting monitors. However, many monitors are found opportunistically near dwellings and are collected. Their skin is used as a poultice in traditional remedies for skin diseases. We were also told that monitor skins stored in tents or houses keep snakes away.

The desert monitor, as the only representative of the Varanidae in the country and an emblematic species of desert herpetofauna, is highly sought after by naturalists. These groups often explore reservoirs and wells, thereby offering a second chance to trapped animals that would otherwise perish. However, these practices may sometimes lead to excessive relocations of these animals.

In Morocco, Varanus griseus is classified as "Least Concern" on the national Red List4. Globally, it is assessed as "Least Concern" due to its wide distribution, despite local declines5.

The main threats include:

road collisions8,
habitat destruction,
direct persecution by humans1,
accidental mortality due to falls into matfias (traditional wells), pipeline inspection shafts, cisterns, and agricultural reservoirs8.

In Morocco, it frequently falls into wells, reservoirs, or pipeline inspection shafts, where it can remain trapped, representing a significant threat to the species8. During our expeditions, we found dead individuals in agricultural reservoirs, sometimes several individuals in the same location.

Finally, the species is listed in Appendix I of CITES, strictly prohibiting international trade for commercial purposes2.

Dead Monitor lizards in a water retention basin in an agricultural area, in the middle of an otherwise very arid region.

Agricultural water basins, deadly traps for Monitor lizards

The agricultural basins in question, deadly traps for many Monitor lizards every year.

Dead Monitor lizard in a pipeline inspection shaft

A Monitor lizard found dead and decomposing in a pipeline inspection shaft near a city.

A whole dried Monitor lizard for sale in Jemaa el-Fna Square in Marrakech.

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Zdunek, P., Bouazza, A., & Martínez del Mármol, G. (2024). Dragons in desert trouble: Anthropogenic wells as a potential threat to the Desert Monitor, Varanus griseus (Daudin, 1803), in Morocco. Herpetology Notes, 17, 821–826.
Zima, Y. (2019). On the Toxicity of the Bite of the Caspian Gray Monitor Lizard (Varanus griseus caspius). Biawak, 13, 115–118.
Zima, Y. A., & Fedorenko, V. A. (2024). The range of the Desert Monitor Varanus griseus caspius (Eichwald, 1831) in Central Asia. Frontiers of Biogeography, 17, e138199. https://doi.org/10.21425/fob.17.138199