May, 2008

Golden Tortoise Beetle

The little jewel featured this month is a golden tortoise beetle (Charidotella sexpunctata). This insect is about 1/4 inch in length and feeds on plants in the morning glory family, Convolvulaceae. I often see them on purple bindweed (Ipomoea trichocarpa), and in our yard they like the Alamo vine (Ipomoea sinuata). As with many members of the Chrysomelidae family, or leaf beetles, when these tortoise beetles feed they produce numerous small holes in the foliage of the plant. However, they are not usually too abundant, so the damage is negligible.

The golden tortoise beetle has a neat trick that it can do when disturbed. In a split second, it can change from the bright metallic gold pictured above to a flat orange color, complimented with six black spots, hence the species name "sexpunctata." The reason for this transformation is to fool predators: the tasty leaf beetle suddenly resembles a distasteful ladybird beetle. Having the same shape certainly helps in this masquerade. The metallic and somewhat iridescent color is produced by the microscopic structure within the beetle's cuticle. The color change is a result of fluid being pumped in or out of tiny cavities which then alters the way light is reflected. Because these beetles change so easily, it is especially tricky to photograph them without disturbing them; I have far more photos of their orange color morph than of their pure golden one.