×Courtship begins with the animals circling each other quickly for a few minutes in concentric circles (the female on the inside), the male apparently trying to bite the temporal region of the female, but without succeeding since the heads are always parallel. Occasionally the male does bite the flank or tail of the female, though without maintaining his grip. Quite suddenly copulation occurs, preceded by a second or two in which tails and legs seem to become a twirling jumble. In the first 10-20 seconds of the copulation the male, mailny, shows quick frontleg- and tail-movements. There is not bite-hold on the female; the male may even sit in an ´upright` position with neither his head, frontlegs nor front part of his body touching the female. However, after a maximum of approxomately tebn minutes, the male returns to the usual horizental position. Copulation lasts about 45 minutes, after which the pair separates.
In 1995 a clutch of four eggs was laid in the first week of May, a second with three eggs in the third week of June. Eggs measured 9.6 x 16.9 mm and weighed 0.88 g. Just before hatching these reached 18.3 x 30.0 mm and 5.65 g. Incubation at 20°C takes 43 days. Young measured 30.6 + 43.2 mm (head-body + tail) and weighed 0.96 g.
The juvenile skin patter consists of seven longitudinal, yellowish lines on a velvet, black body. On the flanks a longitudinal series of dull, yellow dots is found. Vemntrally the head and body are off-white. In contrast to what is known of all other Acanthodactylus species, juveniles of Acanthodactylus erythrurus belli show a bi-coloured instead of a uni-coloured tail. Dorsally and dorsolaterally it is turquoise, laterally and ventrally it is a saturated red. Since there is no clear demarcation line between the two, and because the final colour impression is somewhat dependet on the angle of observation, hues between blue via lilac to brown and red result. Except for some striping and banding in other lacertids, mostly concerning shades of the same colour, this bicoloured tail is also unique within the family Lacertidae. Even in the closely related Acanthodactylus e. erythrurus juveniles show only uni-coloured red tails.
The impression is that a blue juvenile tail may be ´primitive` in Acanthodactylus; in the majority of species it still is that colour. It changes to blue with black transverse bands in A. schmidti, whitish blue in A. gongrorhynchatus and yellowish in A. haasi, A. micropholis and Egyptian A. longipes. Red tails occur in African A. boskianus, in A. e. erythrurus and A. opheodurus. In some species the colour is most intense distally and dorsally, but fades anteriorly. At the other extreme of the spectrum it is strong on the tail underside and also occurs on the back of the thighs. Presumably the former, which concentrates attention towards the tail tip and away from the more vulnerable body, distracts predators. The latter case, being striking from a lizard´s eyeview, especially if the tail is lifted, could be an intraspecific signal which in analogy to literature on Eremias may reduce agression in mature males.
Sympatric Acanthodactylus species often differ in immature tail colour; this may help prevent predators developing a universal Acanthodactylus search image. It may also serve an interspecific function allowing adults to recognise and eat other species´ young.
It may thus be that tail colour has two distinct puposes, in which case there may be situations where the optimum colours for signalling to conspecific and to predators are different. However, if so, it is surprising that bi-coloured tails are extremely rare. Maybe too much conspicuousness is detrimental?
At an age of six months the remaining blue tail colour in A. e. belli is only just visible on an oblique angle, although the red – albeit less intensive – still shows. In the present case with young A. e. belli one might hypothesize that blue, possibly performing an interspecific function is less necessary (in the grown juvenile), but that, the presumably intraspecifically active red, apparently still is useful (like in the closely related A. e. erythrurus where in females it may persist into young adulthood). An additional three months later most of the tail colour has disappeared, the tail being only veguely greenish from a distance (the combined effect of light blue and light red).
In adult A. e. belli most of the black and all of the tail colour changes into brown or brownish-grey. Some of the black persists as rows of black markings on the body. The yellow lines disappear for the greater part (in males) or change into grey or white (in females).
