Butterflies in the genus Acraea – such as the Acraea Elegant, Acraea egina, feed selectively on plants with cyanoglycosides (poisons!) belonging to plant families such as the Passifloraceae (the Passion Flower family). So they are brightly coloured to advertise that they are poisonous, or at least distasteful to birds and other predators; and as such they serve as ‘models’ and are ‘copied’ in apearance by other butterflies which are not poisonous, i.e. Batesian mimics. An evolutionary strategy to benefit from another species without having to go through the process of eating all those nasty poisons oneself! Acraea egina is mimicked very closely by another nymphalid, called Boisduval’s False Acraea, Pseudacraea boisduvali, and by a swallowtail, Papilio ridleyanus!
Butterflies in the genus Acraea engage in what has been called by an Victorian lepidopterist, Marshall 1902 (Eltringham 1912), “marriage by capture”, to describe the fact that the males seize the females in the air. A remarkably detailed description of this process was described by Ward (1995) (2).
“The male Acraea (Acraea) acara approached the female at speed from behind and slightly to one side. The female was flying in a leisurely fashion up the slope of a grassy hill. The male attacked the female much as a raptor would attack its prey in flight. The male hit the female at full speed with his legs, striking her on the side of the body at the base of the hindwing underside. The female was grasped tightly by the male preventing her from flying and the pair spiralled to the ground. The male held the female tightly to the ground with her head pressed into the base of a tuft of grass. The male then curved his abdomen around until he managed, with difficulty, to engage his genitalia with that of the female. Almost instantly on penetration the male became comatose and slowly, with wings folded, fell sideways to the ground.
The female extricated herself from beneath the male and out of the tuft of grass. After a brief breather she flew away with her mate hanging down behind.”
Amazing stuff you come across in entomological journals!
Confusingly, Acraea egina is itself a mimic of sorts – a Müllerian mimic of Acraea zetes – which together with a number (about seven) of other butterfly species, forms what has been called a mimicry ring. The unpalatable species in the ring resemble each and converge to present a common pattern to predators, so that if say a bird learns by experience to avoid one species in the group, they all benefit from the fact that they look closely like that species.
It’s all very confusing and I am starting to wonder whether I have got the model or the mimic (or one of its friends!)!.
1) ELTRINGHAM, H ., 1912. A monograph of the African species of the
Genus Acraea Fab. Trans. ent. Soc. London 1.
2) Ward, Peter (1995). “180 METAMORPHOSIS, VOL. 6, No. 4 December 1995. LEPIDOPTERISTS’SOCIETY OF SOUTHERN AFRICA: 180.