Habitat, behaviour and ecology
Throughout its range the Diadem snake can inhabit a fairly wide range of different habitats, from deserts and semi-desert to agricultural land, although it tends to avoid extreme desert. It can be found in open, sparsely vegetated and stony environments such as steppes; areas of dispersed shrubs and annual grasses; on sandy or clay soils; in rocky, hilly and mountainous regions up to around 6500 feet (2000m). It is tolerant of anthropogenic change and can also be found in ruins, on the fringes of settlements and even urban areas.
These snakes are active both by day and night although never in the hottest parts of the day. They are often seen basking in the early morning. In the heat of the summer the snakes forage in the evening and night.
This species of snake is fairly opportunistic in its prey. Adults are known to eat mammals, for example gerbils (Meriones), birds and lizards for example Agamids (Trapelus spp.) and Lacertids (Eremias spp.). Juveniles probably eat lizards. Adults seem to prefer warm blooded prey.
Diadem snakes latch onto their prey and wrap around them, constricting them although not as efficiently as rat snakes or king snakes. While this genus has been described as ‘non-venomous’ by many works of literature as recently as 2018, studies have found toxic elements to their saliva with an LD50 of 2.75 μg/gm in mice which may be used to subdue struggling prey. To my knowledge there is no record of any venomous symptoms in a human after a bite from a snake from this genus, although several older books warn that the Royal Diadem snake may be mildly venomous.
Diadem snakes share more derived characteristics with vipers than almost any other ‘Colubrid’ genus. It has been noticed that this genus may mimic various vipers that share its range (in particular Pseudocerastes fieldi and the various Saw-Scaled vipers, Echis spp with which it shares almost the entirety of its range). The snake heightens this viper impression by flattening its head in a triangle and making coiling movements when disturbed. It also produces long, loud, drawn out hisses that are very impressive for a snake this size. Diadem snakes have a modified preglottal structure that, while not as advanced as the epiglottis of Bull and Gopher snakes (Pituophis spp), still enables very loud hisses. The sound and duration of these hisses, and the coiling movements of the body, may also mimic the saw-scaling of the deadly Saw-Scaled vipers (Echis spp) as well.
When disturbed, the first instinct of the Diadem snake is to flee, which they can do with rapidity. But if cornered they coil and hiss and put on quite a performance. They are also capable of opening their ‘lips’ into a pronounced snarl which gives them a ferocious appearance. Should a would-be predator ignore these warnings the snakes will escalate by striking repeatedly and without reservation.
In the wild, males perform combat behaviour from April to May and courtship in this species occurs from May to June. Upon coming across a female, the male will pursue her; if the female is unreceptive she will lash her tail, bite at the male aggressively and he will break off the chase. Male Diadem snakes do not bite the females during mating the way males of other genera such as Zamenis and Coronella do and female Diadem snakes that are receptive to mating allow the male in their vicinity without defensive biting. Indeed, receptive females seem quite amenable to mating and the courtship phase and mating phase are relatively quick compared to other snakes. The male courts, mounts the female with a series of side-to-side movements, lifts her tail with his and begins copulation in a process that can take as little as three minutes and up to half an hour. Mating itself can take a long time, usually between six to eight hours, during which and for some time after the female’s cloaca bulges grossly.
The female lays her clutch of eggs, usually between 5 to 16, in July to August. The eggs hatch in September to early October after around 60 days incubating.