10 Traits That Make Insects Survivors

If you want to survive, it helps to be flexible. Eat what's available, time your bodily cycles to local conditions and don't put all of your eggs in one ecological basket. As a class, insects are masters of flexibility, both in terms of genetic adaptation and phenotypic plasticity — the way one set of genes can produce physical traits that vary in response to diverse environments [source: Whitman and Agrawal].

Insects account for nearly 73 percent of all known animal species and for almost 85 percent of land animal species. So far, we've found and named around 900,000 species, divided into 32 orders. Experts estimate that the true number could reach much higher, in the range of 2-30 million [sources: Danforth, Smithsonian]. The larger estimate derives in part from the amazing variety of insects that dwell in South American forest canopies [source: Smithsonian].

Their wide ranges of physical and social traits, and their notable adaptability, enable insects to spread into nearly every open niche. It also partly explains why insects survive mass extinctions [source: Yeates]. But even creatures as flexible as insects require a lot of time to radiate into so many wondrous forms.

The same factors that drive insects to branch out into species today have also driven large-scale changes in the distant past. These include mutation, natural selection, migration, isolation and genetic drift, the tendency of some offspring, and their genes, to survive due to random forces not related to adaptation. However, the rise of such new clades, or groups of species, like bees or beetles, requires far longer stretches of evolutionary time [source: UC Berkeley].

Insects first appeared at least 450-500 million years ago. Their ancestors evolved from crustaceans, and the earliest creatures that we'd recognize probably looked like modern silverfish (Lepisma saccharina). A major flowering of species 100-150 million years later produced grasshoppers and cockroaches. Insect groups like flies, wasps and beetles made the scene around 200 million years ago [sources: Misof et al., Yeates].

Each group represents specializations made possible by large spans of time. Over eons, the clades radiated into species adapted to numerous land and freshwater niches [source: Misof et al.]. This process profited not only from time, but also from the survival value of high fertility rates and large broods in many species.

Population-wise, we might as well dispense with the idea that we run the planet. A population of 7 billion might sound large to us endoskeletal bipeds, but it's peanuts next to roughly 10 quintillion (10,000,000,000,000,000,000) living insects. The population of the United States measures around 320 million. Some soil studies have found that many insects in a singleacre [source: Smithsonian].

For insects with high mortality rates, fecundity means survival. But bountiful babies offer evolutionary perks as well. Large populations help insects make the most of new niches and prospects. They also help insects develop resistances to whatever bug juice we throw at them. Fitness traits develop through random favorable mutations, and large populations mean large numbers of tickets in the genetic lottery [source: Yeates].

In addition, population pressures push insects to spread out. More geographic isolation and less gene flow from one end of the populace to the other helps to bring about new species. For existing species, large populations help ensure stability by lessening the impact of genetic drift [source: UC Berkeley]. They also face fierce rivalry within their ranks, a problem some insects deal with using a little social engineering [source: Capinera].

Evolutionarily speaking, insects pioneered social structures [source: Misof et al.]. Today, the 2 percent of known species that have this trait make up roughly four-fifths of the planet's insect biomass [source: Johnson and Carey]. What's more, taken together, their ecological impact can outclass just about any other animal. South American leafcutter ants, for example, chow down on more plant life than all plant-eating mammals on that continent combined [source: Meyer].

True social, or eusocial, species share four key traits. Their members occupy a shared nest site; team up to raise young; split labor between sterile (or less fecund) workers and reproducers; and live side by side with overlapping generations. Although many insect species have one, two or even three of these traits, only a few have them all. They include all termites, all ants, 600 species of bees (family Apidae) and 700 species of wasps (family Vespidae) [source: Meyer].

Of course, social structures carry risk. Infectious diseases and specialized parasites can wreak more havoc, and members must vie with one another for resources. But weighed against a large, expert and robust workforce for building, food gathering and defense, the rewards of a large social populace become clear.

The jointed limb quite literally defines the phylum to which insects belong. It's right there in the name Arthropoda (from Greek arthros (jointed) and poda (foot)). But in insects, these members form more than just limbs. They are the basis for everything from antennae to mouthparts [sources: Fleury, Wigglesworth].

Insects likely evolved from a critter made up of numerous similar leg-bearing segments, not unlike a simple centipede. Over time, these parts fused to form the familiar head, abdomen and thorax of modern insects, while their connected legs changed to take on roles from sensing to stinging. An insect's head, for example, consists of six primitive segments, the modified legs of which now serve as antennae and specialized mouthparts [sources: Fleury, Wigglesworth].

And we do mean specialized. If you think a shrimp fork is a specific utensil, try mouthparts with cutting edges, or with tubes and grooves that assist both bloodsuckers and nectar-feeders [source: Wigglesworth; Mitchell and Scott].

One all-or-nothing approach to survival is to become essential to something else, to bind your fates so tightly that you live or die as one. In nature, such mutualism can entail risks, but it can also pay dividends by securing food and shelter for insects and their offspring. Mutualism takes many forms, the most extreme of which, coevolution, involves species influencing each other's evolution.

Insects and plants do not have a monopoly on coevolution or mutualism, but genetic research suggests that they have evolved in tandem virtually from the beginning [source: Misof et al.]. This long history has led to numerous hand-in-glove relationships between the two. Acacia ants live in the thorns of acacias and protect them from herbivores, while the trees' leaf tips provide food for the ants. Yucca flowers, for example, have shapes that only allow the yucca moth to pollenate them. After pollenating, females lay egg in the yucca. When they hatch, her caterpillars will eat some of the seeds but leave enough for rodents to disperse [source: Carter].

Enduring drastic changes as you grow might sound like a giant hassle — most of us can barely hack puberty — but it offers its share of benefits.

Most insects undergo major changes in their bodies, biochemical makeup and behavior as they mature. Primitive insects go through a partial metamorphosis in which a few body parts, such as sex organs, mature over time. In such species, juveniles and adults bear some resemblance. Advanced insects, conversely, go through a change so complete that they appear at some stages to be different animals. In the larval stage, their bodies are built to chow down and beef up. Later, they assume an inactive transitional form, or pupa, that tears them down and reshapes them into an adult body built for spreading out and making babies [sources: Meyer, Museum Victoria].

Complete metamorphosis means that juveniles face different predators and don't vie with adults for food. It's a useful way to spread the odds. Perhaps that why, although only nine out of 28 orders go through it, they account for 86 percent of all insect species [sources: Meyer, Museum Victoria].

Insects developed wings around the same time plants began growing upward — more than 100 million years before the first reptiles flew [sources: Meyer, Yeates]. The closest modern equivalents to these pioneers of flight are mayflies and dragonflies, although ancient dragonflies sported 24- to 28-inch (60- to 70-centimeter) wingspans [source: Yeates]!

Flight helps insects spread into new areas, migrate, escape predators and reach out-of-the-way food sources. Some sportier models of insect come equipped with foldable wings, a handy trait for squeezing into tight spaces like nests or tunnels [source: Danforth].

Insects are the only invertebrates that fly. They're also the only winged animals that did not give up a set of limbs in order to gain wings [sources: Meyer, Yeates]. The speed and agility they display in flight, the heavy loads they can carry, and the strange flight mechanics involved continue to inspire research by physicists and aeronautical engineers [source: Meyer].

When flying, insects use about as much energy (calories per unit of lift) as do birds and bats, but they excel at converting that energy into power. Insects store and release energy with spring-like efficiency because their bodies are both flexible and resilient, thanks in part to their exoskeletons [source: Meyer].

Instead of bones, insect bodies are supported by a skeleton that covers their outsides. This exoskeleton consists chiefly of chitin, a substance that can take forms raging from rubbery to rigid and from supple to steely. It not only protects the insect from damage or drying out, it also houses sensory organs, includes breathing holes called spiracles and, like our skeletons, provides a place for muscles to attach [sources: Encyclopedia Britannica, Meyer].

Exoskeletons also account for insects' notable strength and flexibility. Fixing internal muscles to an outer body wall instead of an inner skeleton boosts mechanical advantage, which partly explains why many insects can heft loads that weigh many times their own body weight. Insect bodies remain flexible thanks to supple tissues at the plate joints, and their internal squishiness lets them squeeze into small spaces to escape predators, seek food or hide from the elements [source: Meyer].

Like most adaptive features, exoskeletons have drawbacks. When an insect grows, its shell stays the same size, so it must shed it in a process called molting. After molting, the insect remains at risk until a new exoskeleton forms [sources: Encyclopedia Britannica]. Exoskeletons also limit how large insects can grow — in time, the need for more muscle outstrips available attachment areas — but that's just as well, because being small has survival value, too.

Insects push the boundaries of smallness. Midnight movies to the contrary, there's only so large an exoskeleton-based creature can grow — theoretically, around 4-5 ounces (125-150 grams) [source: Meyer]. The largest living insect, the cricket-like New Zealand giant wētā, or wētāpunga, weighs about half that (but still outweighs a mouse or a sparrow!) [sources: NZDoC, The Telegraph [UK]].

One the smaller end of the scale, insects are wonders of miniaturization. Shakespeare's Hamlet spoke figuratively when he said, "I could be bounded in a nutshell, and count myself a king of infinite space." But some ant species establish entire colonies inside of acorns [sources: CISEO; Meyer]. Moreover, the smallest insects, such as the Costa Rican wasp Dichomorpha echmepterygis, can reach sizes smaller than some paramecium (single-celled protozoa) — 0.00055 inch or 0.139 millimeters. The majority of insects fall into the 0.1-1.0 inch (2-20 millimeter) range [source: Meyer].

Tiny creatures enjoy several advantages. They need only the tiniest morsel or drop to sustain their bodily needs, hide from predators in nearly any setting and find shelter and shade wherever they might be. To them, a pebble is a boulder and a tiny crack, a fissure. You might say that, for insects, the world is incredibly small and therefore unspeakably vast.