Is this a golden tortoise beetle?
The great outdoors can produce baffling mysteries. MVTimes Wild Side columnist Matt Pelikan tries his best to solve them. Got a question for the Wild Side? Send it to firstname.lastname@example.org
Dear Wild Side,
I found this beautiful bug in an equally beautiful tulip today. Pretty sure it’s a golden tortoise beetle, but thought you could elaborate for our readers?
The Pelikan brief:
Interesting little beetles — the use by larvae of feces cakes as a defense mechanism is quite amusing!
The longer answer:
This odd creature is a so-called “tortoise beetle,” named for its vaguely turtle-like shape. The beetle’s exoskeleton extends outward, forming a transparent apron, which may offer protection from predators. As is often the case with common names for insects, “tortoise beetle” is really a generic term: taxonomically speaking, tortoise beetles are a “tribe” or part of a sub-family, with about 30 species occurring in the United States and more than 1,700 existing worldwide. I can’t tell for sure which species Danielle photographed, but only a few tortoise beetles occur in our region, and of these, the species that seems closest to Danielle’s bug is Charidotella purpurata. Like the vast majority of insects, this beetle is not well enough known to have acquired an English name, though it’s a widespread and apparently fairly common species. Another possibility is Charidotella bicolor, known as the golden tortoise beetle, a close relative which is also widespread.
Tortoise beetles, both larval and adult, feed on plants, and in general this group specializes in eating members of the plant family Convolvulaceae (this is the family that contains, among other plants, the sweet potato and the morning glory). In warm climates, some kinds of tortoise beetles can be agricultural pests, devouring enough sweet potato leaves to damage a crop. But these beetles do not appear to be especially common on the Vineyard, and sweet potatoes are not a local crop, so it is safe to assume that Danielle’s beetle is doing nobody any harm. (Ornamental sweet potato vines are widely available as annual container plants, and it might be fun to grow one and see if tortoise beetles turn up on it.)
Tortoise beetles lay eggs in spring, usually on the underside of the leaves of the plant the adult prefers to feed on. The eggs hatch into remarkably homely larvae, flattened, slug-like, and equipped with branching spines. The larvae of some species are said to assemble a sort of shield, consisting of debris pasted together with feces, which they hold over themselves as protection from would-be predators. It would surely deter me! Tortoise beetle larvae mature over a period of a few weeks, pupate, and emerge as adults, and then enter a dormant state called “diapause” to overwinter. The onset of warm weather rouses the adults, which seek out an appropriate food source, and mate and lay eggs if they are female, starting the next generation.