Thursday, April 8, 2010

Crow Butterflies

and some Lookalike Moths
(Euploea core corinna and Cruria donowani)
These “common crows” were indeed common at Irongate reserve last weekend - here seen feeding on a Zinnia flower. (The zinnias we see growing wild on the Darling Downs are garden escapees from Mexico, very popular with butterflies.)
Crow butterflies breed on climbers of the Apocynaceae family -  Parsonsia species and their closely related cousins the Marsdenia vines. There are several species of each growing at Irongate, all vines with opposite leaves. The Marsdenias can be distinguished from the Parsonsias by the white sap which wells out of broken stems. (See an article on Marsdenia viridis, March 2010)
Crow butterflies are common despite the destruction of much of their native bushland, because they are also able to breed on the poisonous introduced plant, oleander. They are so often found on oleander bushes there that some people know them simply as “Oleander butterflies”. They are easily distinguished from other black and white butterflies by their polka-dotted bodies, and by the fact that they seem to have only four legs. (Actually, they do have the regulation six, but the front two are small and kept tucked up against their bodies.)
As caterpillars, they absorb poisons into their bodies from their host plants. These are retained in the bodies of the adult butterflies, and protect them from predation by birds.

A curious insect common at Irongate at the moment is this “crow moth” (Cruria donowani). It is a day-flying moth, always flying within a few feet of the ground, and not poisonous at all - but it keeps itself safe from birds by imitating the poisonous crow butterfly.
The wings are very like, though somewhat narrower, but the body is very different - tiger striped rather than polka-dotted, and having an orange “tail end”.
Crow moths are known to breed on a number of different plants, but at Irongate they are probably breeding on the little “tar vines” (Boerhavia dominii) which are common there.

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