If you were an insect, you wouldn’t think about much at all. But to the extent that you did think, how to avoid being eaten would be a major topic of contemplation.
Birds, spiders, mammals, other insects — pretty much everything out there eats insects under at least some conditions, and avoiding that fate long enough to mate and, if you’re female, to lay eggs is the name of the game for a bug.
There are countless strategies to avoid becoming dinner. In the order Hymenoptera, wasps, bees, and even some species of ants rely on retaliatory stings to deter would-be predators. Blister beetles exude irritating juice from the joints when they’re disturbed. Monarch butterflies store up unpalatable chemicals from the milkweeds their caterpillars feed on; a bird may eat one monarch, but it’s said the experience dissuades them from trying a second.
Insects with a reliable means of self-defence often advertise their presence with bright colors, almost daring a predator to attack instead of staying hidden (think of the black-and-yellow bands on a yellow jacket wasp). And the imitation of these warning color patterns in defenseless insects is likewise a common strategy — many flies in the family Syrphidae, for example, are unarmed but closely resemble stinging wasps or bees.
Many other insects leap, fly, or run to escape danger, and generally they have acute vision, especially for the detection of motion, that gives them early warning. But if there is a most widespread approach to staying off the menu, it’s the simplest one: simply not being spotted in the first place. Across the vast class Insecta, countless species have honed invisibility into an art form. If a predator doesn’t notice you, it won’t eat you.
Mere concealment is one approach. Insect larvae that eat plants tend to feed from the underside of leaves, concealed from predators such as birds that would attack from above. Many other kinds of insects spend most of their time buried deep in leaf litter or thatch — ground crickets come to mind, half-inch relatives of the more familiar field crickets. They’re abundant, as you can tell if you learn to recognize their calls. But actually spotting a ground cricket is a rare event, since they are rarely in the open and scuttle deftly away if you try to uncover them.
But for me, the most interesting approach to staying is unseen is the use of camouflage or protective coloration. Concealing colors or patterns can be astonishingly effective, and almost as impressive is the instinctive reliance on their camouflage that some of these insects exhibit.
Take the grasshopper Psinidia fenestralis (sorry, it has no common name). This is an uncommon butterfly on the Vineyard, though its overall range is quite wide — I’ve found it only at a single location in Oak Bluffs. And even there, this grasshopper spends most of its time in a very specific micro-habitat: Bare, gravelly, compacted soil with sparse, often dried-out vegetation.
About an inch long, Psinidia is colored in a mottled mix of brown, gray, and off-white. Across its range, the species varies widely, with the mix of colors customized to match its favored habitat. When I’m trying to photograph this grasshopper, I often lose sight of my subject, even though I’m within inches of it. And the grasshoppers seem aware of their immunity – they will sit still almost until you touch them when they’re resting on their preferred substrate, while they’re quite twitchy if you catch them in a setting where their colors clash with, say, green vegetation.
Another grasshopper, Trimerotropis maritima, shows similar talents. On the Vineyard, this good-sized grasshopper is restricted to seaside dunes, where the ghostlike shading of our local population is nearly invisible against the background of our typical beach sand. Elsewhere — this species ranges across much of North America – T. maritima varies to match the local sands uncannily closely. Same species, different look.
Or consider our larger katydids, hefty insects around two inches long. The Vineyard has about a half-dozen species, all of which possess broad, green wings that closely resemble leaves. Again, a katydid on bare ground can be a wary beast, launching into unsteady but surprisingly brisk flight when disturbed. Typically, they land a few feet off the ground in a bush or shrub; clutching a twig and holding utterly still, they impersonate leaves and are fiendishly difficult to spot.
There’s no mystery here, just the process of natural selection at work. A defenseless insect that can stay hidden is simply more likely to survive than one that can’t. Over many generations, the individuals that blend in best tend to survive longer and reproduce more successfully, passing on their characteristics to the next generation. And over time, behavioral traits — the instinct, say, to stick to bare soil and stay as still as possible when perched there — can likewise evolve, enhancing the effectiveness of the camouflage.
You can find countless examples of this art form as close as your own front yard. But you’re going to have to look closely to spot them!
