Let's face it: there are a lot of people who wish most insects would go away. Talk to them about projects like the Natural History Museum of Los Angeles County's BioScan, in which regular folks' backyards are found to harbor a surprising diversity of as-yet unknown insect species, and they're likely to reach for the can of bug spray.
Most of us don't choose our phobias, and those of us who react to our six-legged friends with a visceral shudder aren't about to be talked out of that reaction by logical argument. But if learning more about the critters that make up the overwhelming majority of animal species doesn't always help stop the shuddering, it may sometimes help people think twice about spraying.
The elevator version: most insects are either beneficial or at least harmless. Some of them are beautiful and fascinating. And without them, life as we know it would not exist at all.
Basics first. Insects are a gigantic, closely related group of species in the arthropod phylum. Scientists are split over whether they're more closely related to crustaceans such as lobsters and crabs, or to millipedes and centipedes. Regardless of what those scientists eventually decide, it's easy to tell insects apart from their relatives.
If an animal has a three-segmented body (head, thorax and abdomen) covered in armor called an exoskeleton, three pairs of jointed legs, compound eyes, and a pair of antennae, it's an insect. If it's got a different number of body segments or more than six legs? Not an insect. Spiders and scorpions? Not insects. Centipedes? Not insects.
Even with those non-insects ruled out, the planet still boasts a staggering number of insect species. A million have been described by scientists. Estimates of the total number of insect species, including those yet to be discovered and described, range from 6 million to 10 million.
Compare that diversity to mammals, with probably about 6,000 species, including those yet to be discovered. Or birds, of which there are around 10,000 species. For each species of mammal or of bird, there are around 1,000 insect species. By most estimates, nine out of ten animal species on the planet are insects.
If you add all other vertebrates to the scale on our side, with reptiles, amphibians, and fish added to birds and mammals, that still only comes out to about 64,000 known species. Vertebrates are completely outclassed by insects in the diversity department. And the vertebrates most of us know best are outclassed in the seniority department as well. The first true mammals evolved something like 220 million years ago, and birds about 70 million years after that. Insects, on the other hand, have been walking, crawling, and flying around on planet Earth for about 400 million years. Most of the insect body plans we'd easily recognize today were already here 300 million years ago.
With 90 percent of the animal species on the planet being insects with a 400 million-year track record, alien scientists visiting Earth for the first time might well decide it's the planet of insects.
And those insects have shaped the rest of the living world in ways so profound it's hard to grasp them. When insects had only been on the planet for about 200 million years some of them found themselves building an evolutionary partnership with certain plants. Insects feeding on pollen may have inadvertently moved that pollen to plants' female reproductive organs, helping the plant produce more seed than if it had relied on wind or water to do the pollen spreading. Plants that attracted insects to their pollen set more seed, and they evolved a whole range of strategies to attract them: modified leaves with bright colors; sugary nectar; pungent scents that insects' sensitive nervous systems could detect over miles.
In other words, if there weren't insects, there wouldn't be flowers. Other animals such as hummingbirds and bats pollinate flowers as well, but the vast majority of animal pollinators are insects. Aside from the honeybees that everyone's so worried about these days, and with good reason, there are about 200,000 other insect species that pollinate plants, from the yucca moths that have consigned their fate to that of Joshua trees to the astonishing range of insects that pollinate tropical orchids.
So insects made flowers, to oversimplify only slightly. That's good, because our planet would be a lot more drab if all we had to look at were plants in shades of green and brown. It's also important in helping us not starve to death: most of the non-animal foods we eat come from flowering plants, and many of those wouldn't reproduce if not for insect pollinators.
If it wasn't for insects, the only plant food we'd have would be from plants that have some other way of spreading their pollen around, usually just by letting it fly on the wind and hoping it lands in the right place. If all insects disappeared tomorrow, you'd pretty much have wheat and corn, cabbages, and some tree nuts to eat next year. There'd be a few crops from plants that are partly self-pollinating, like tomatoes and peppers and green beans, but without the help insect pollinators provide, it'd be a lot harder to produce the produce.
That's if our current insect cohort disappeared tomorrow. If they'd never existed, we'd be eating ferns and pine nuts. Common food crop plants that rely on wind or on their own devices for pollination may not need insects now, but they very likely evolved from plants that did. It's thought that even grasses evolved from ancestors that needed insects to reproduce. No insects? No ancestors, and no grasses evolving from them.
Without picnic-invading insects to squash, in other words, you'd have no squash. And no salsa, because you'd have no onions, chiles, tomatoes or tomatillos. And no tortillas, either corn or wheat. And no carne asada, because grass-eating cows would never have evolved.
So next time you're enjoying a picnic and you see ants trying to climb onto your tacos, try to summon up a little gratitude. They made them for you.