Tortoise beetle larvae protect themselves from predators by<\/p>\n
creating a shield of ‘distasteful’ items collected on forked<\/p>\n
structures at the tip of the abdomen.<\/p>\n
July 18, 2014<\/p>\n
Tortoise Beetle<\/p>\n
Thar’s gold in them thar hills!<\/p>\n
But hold on a sec. Before you run for your pans and pick axes, we should probably clarify a couple<\/p>\n
things. One, the hills in question are located in the Hickory Knolls Natural Area, where no digging is<\/p>\n
allowed. And two, the gold isn’t the precious-metal type, though it is indeed a treasure \u2013 especially if<\/p>\n
you like bugs.<\/p>\n
What we’re talking about this week are golden tortoise beetles, Charidotella sexpunctata. As we have in<\/p>\n
summers past, we once again have discovered these little gems–a fairly common species in our area–<\/p>\n
hanging out on bindweed, one of the insect’s favored food plants.<\/p>\n
Thanks to some built-up fluids and a really neat optical illusion, these beetles look for all the world like<\/p>\n
drops of gold glistening in the sun.<\/p>\n
As I stood there admiring their beauty, I realized that, once again, I was going to miss out on an<\/p>\n
opportunity to snap a photo of these truly glorious creatures. I did have my phone with me, but its<\/p>\n
ability to capture tiny things like tortoise beetles (which are about \u00bc-in. in length) combined with my<\/p>\n
own limited photography skills, meant a mental picture was as good as it was going to get.<\/p>\n
I consoled myself by giving the beetles a couple of light pokes.<\/p>\n
I know, it sounds bad, as if I were taking out my<\/p>\n
disappointment on some poor defenseless<\/p>\n
arthropods. But my intent was not to harm them;<\/p>\n
rather, I just wanted to see the beetles change color.<\/p>\n
And, did they! In a flash they transformed from rich<\/p>\n
metallic gold to a still-shiny, but much less impressive<\/p>\n
reddish-orange.<\/p>\n
Researchers are divided on the purpose behind this<\/p>\n
behavior. Does it confuse predators? Is it an attempt<\/p>\n
to mimic ladybugs, which use chemical deterrents to<\/p>\n
avoid getting eaten?<\/p>\n
While the reasons may be murky, the science of how it occurs is not.<\/p>\n
The beetle’s normal \u2013 or “at rest” \u2013 golden hue is created when light reflects off liquid that is held in thin<\/p>\n
grooves between the layers of the insect’s transparent elytra, or wing covers. But when the beetle is<\/p>\n
agitated or stressed, it drains the moisture away, revealing an underlying color of ladybug-red, spots<\/p>\n
optional. The color change also can occur during periods of extreme drought, when the insect might not<\/p>\n
have an adequate moisture intake, as well as when the insect dies.<\/p>\n
Being able to change color is a cool trick, as anyone who’s ever observed it can attest. But this species<\/p>\n
displays an even more interesting behavior that has no doubt saved the lives of many young beetles<\/p>\n
over the ages.<\/p>\n
As larvae, tortoise beetles are dark in color, with soft, fringed spines along their sides and a two-pronged<\/p>\n
“anal fork” at the rear of their abdomen. Quite a bit of ornamentation for a young insect no bigger than<\/p>\n
a collar button. But it gets better.<\/p>\n
That forked appendage is good for more than just looks. It’s also a collection device.<\/p>\n
You’re probably wondering what, pray tell, might a beetle larva need to collect? The answer is twofold:<\/p>\n
shed skin and fecal matter.<\/p>\n
So now you’re probably wondering\u2026 why?<\/p>\n
Shed skins and fecal matter, as you might imagine, are distasteful, and generally are regarded as items<\/p>\n
to avoid. But if you happen to be a helpless beetle larvae, jam-packed with nutrients other creatures<\/p>\n
might find useful, distasteful is exactly what you want to be.<\/p>\n
Over time the shed skin and droppings build up on the fork, arching over the young beetle like an<\/p>\n
umbrella \u2013 a poop parasol, if you will. In theory, it’s a great defense against predators.<\/p>\n
But no defense is perfect. (If it were, we’d be overrun with tortoise beetles!)<\/p>\n
For example, members of the insect order Hemiptera, the true bugs, are equipped with piercing\/sucking<\/p>\n
mouthparts. Picture a dinky, hinged drinking straw permanently attached to a bug’s head and you’ll<\/p>\n
start to get the idea. While many species use their straws to feed on plant juices, others plunge their<\/p>\n
predatory probes into animal food sources \u2014 such as tortoise beetle larvae.<\/p>\n
Piercing, sucking predators notwithstanding, tortoise beetles are still pretty easy to find.<\/p>\n
Golden tortoise beetles and their handsome cousins, the mottled tortoise beetles, have a taste for<\/p>\n
plants in the morning glory family; the clavate tortoise beetle, my personal favorite, hangs out on plants<\/p>\n
in the tomato family, namely ground cherries, jimsonweed, horse nettle and nightshades. (Why pick one<\/p>\n
tortoise beetle over another? In a word, charm. The clavate species has spots on its back in the shape of<\/p>\n
\u2014 I swear I’m not making this up \u2014 a teddy bear. Talk about being cute as a bug!)<\/p>\n
The next time you find yourself shaking your head at the invasive bindweed entwined on your<\/p>\n
perennials or the nightshade under your shrubs, take a minute to check them over. You might find you<\/p>\n
have a tiny drop of gold, or even a teddy bear, perched on them thar plants.<\/p>\n
Pam Erickson Otto is the manager of nature programs and interpretive services at the Hickory Knolls<\/p>\n
Discovery Center, a facility of the St. Charles Park District. She can be reached at 630-639-7960 or<\/p>\n