focus on nature

The Undisguised Rainbow Grasshopper Proves It Pays to Advertise

What on Earth is that thing?" My wife, Sue, looks in amazement at the inch-long rainbow grasshopper on the ground near a beat-up little mesquite. This extraordinary insect thumbs its nose at the "rule" that those of grasshopper lineage should be dull brown, dull gray, or dull green. Instead, the rainbow hopper stands out like a garish neon sign on a Western bar, all bright blues and reds and whites.

"Why on Earth does it look like that?" Sue asks, ignoring my identification of the creature by its Latin name, Dactylotum variegatum.

Good question. Most grasshoppers seem dedicated to a life of invisibility. The many dull-brown species usually sit upon dull-brown leaves; the equally common dull-gray ones favor rocks and stones; dull green ones, likewise well-represented, occupy dull-green grasses or shrubs. These cryptic species only leap away when a hiking boot threatens to descend upon them, and when they land they usually blend in so well with their background that they immediately disappear from view again.

A close look at these cryptic species, when we can find them, reveals near perfection in camouflage. The hoppers that sit on dead brown leaves not only exhibit the same hue of leafy brown, they also often possess laterally compressed bodies and thick short antennae, the better to look like a fallen leaf with its petiole stalk. In contrast, the species that perch among gray and white pebbles are marked with patches of light gray and white outlined in dark gray, the better to look like a collection of pebbles deposited at random in a desert wash.

There is no mystery about why these species are so magnificently camouflaged and consequently hard to see. A typical grasshopper's life is full of peril, thanks to a small army of insect-eating birds that like nothing better than morsels of grasshopper for breakfast, lunch, and dinner.

In the past, those hoppers that happened to look like the backgrounds on which they sat quietly during the day had a better chance of living long enough to reproduce than their less fortunate, less well-camouflaged fellows. What we see today is the product of eons of predation, which has left us with the descendants of those prey with the hardest-to-see color patterns.

But what about the rainbow grasshopper? The color pattern of the rainbow grasshopper could not be more different from that of the leaf-, pebble-, and grass-mimicking species that occupy the same Southwest scrublands. Here is an insect that seems intent on committing suicide by visually announcing "mealtime" to all the Cassin's sparrows, kestrels, meadowlarks, and other grasshopper-eating birds in its Chihuahuan Desert home.

A start to solving this puzzle comes from recognizing that not every insect is edible. Take the well-known monarch butterfly for example.

As monarch caterpillars munch their way through poisonous milkweed leaves, certain toxins go straight into the tissues of the larvae and are retained when the insects make the transition to adulthood. Birds that try to consume a monarch caterpillar or adult find the experience unsettling to say the least. The recycled plant toxins not only have a vile taste, they can make monarch-eating birds quite ill.

Most birds find one nasty experience with a monarch more than enough. Thereafter they avoid these insects on sight alone, a task that is made easier for them by the highly conspicuous color patterns of the caterpillars and the striking orange and black combo of the adults.

With the monarch butterfly as our guide, we would be well advised to bet that the rainbow grasshopper is an inedible, and probably downright dangerous, food item for the grasshopper-eaters of Arizona, New Mexico, and Texas.

In fact, various researchers have noted that, for example, desert sparrows avoid bringing the rainbow grasshopper to their nests to feed their young. This is true even though these grasshopperhunting sparrows live in rangelands where rainbow hoppers may constitute nearly 20 percent of the total grasshopper population. Moreover, rainbow hoppers should be easy to catch because they cannot fly and make little attempt to flee when approached.

In experiments with captive predators and prey, biologists have found that when rainbow hoppers were killed they were often left uneaten. This result testifies to the powerful chemical defenses of an insect that knows how to advertise its unpleasant properties.

With its coat of many colors, the rainbow grasshopper offers a warning to would-be consumers and a visual delight to those of us who like to admire but not eat insects.