1.SCOPE AND SCALE
A COCKROACH CAN live without its head for 168 hours. Moths can’t fly during an earthquake. The larva of a Goliath beetle can weigh as much as a McDonald’s Quarter Pounder.
How much of that did you know?
On any given night, you could have up to 10 million dust mites in your bed. The praying mantis is the only animal on Earth with one ear. Bees can recognize human faces. Aphids are born pregnant.
I could go on all day. Really. The insect world is a fascinating place. You might not think so. You might think insects are gross. Or scary. Or dangerous. They get a bad rap, insects. Surveys tell us that 25% of Americans are afraid of insects. They bite. They sting. They carry disease. They ruin our picnics. They look icky. If I asked you to name three icky bugs right now, I’m sure you could do it. You might rattle off spiders, ticks, and centipedes. All super icky, I agree! Except that none of those things are insects.
Huh? Yeah, no. None of those things are insects. Spiders and ticks are arachnids. A centipede is a myriapod. So you can go right on thinking those things are icky. I’m right there with you. Yuck-o! But insects—insects are surprisingly cool. They have many admirable, enviable traits. They have superpowers. And they are among the most successful living things on the planet.
Maybe you’ve never really thought about it before. That’s okay. You’re busy. We’re all busy. It’s not top of mind; I get that. But I’d like to tell you some amazing things about insects, because this stuff is worth knowing. I’ll explain why a little later on, but first I want to tell you what an insect is and what it isn’t. Once I do that, you’ll be able to easily pass the spider-tick-centipede test.
Ready? Okay. All adult insects have three body segments: a head, a thorax, and an abdomen. So right from the start, you know a spider isn’t an insect. It’s only got that tiny little pinhead up front and that big booty in the back. Two parts, not three.
Insects are the only animals in the world that have six legs. Count them up—spiders? Eight. Ticks? Eight. Centipedes? Ha ha, that’s a trick question. I want you to answer “100” because centi-, in units of measurement, means “hundred.” In actuality, centipedes have one pair of legs for each body segment. Depending on the species of centipede we’re talking about, they can have between 15 and 177 pairs of legs. Which is way more than six, anyway. So centipedes are definitely not insects.
What else? Most insects have wings—two pairs is standard, some (flies) have only one pair. Besides birds and bats, insects are the only animals that can fly.1 No wings on our spider, tick, or centipede friends.
Insects usually have two feelers or antennae on their heads that they use for various things, such as smelling, listening, or tasting. Insects are also spineless. Every last one of them. I’m not suggesting they lack courage—I mean it in the literal sense: Insects don’t have spines. They’re invertebrates. You probably know some other invertebrates like octopuses and jellyfish. But insects aren’t squishy and shapeless like those guys because they have skeletons on the outside of their bodies called exoskeletons.
So those are the basics.2 Now you can look at any gross little thing, and without really knowing what it is, you can definitely say whether or not it’s an insect. Dragonfly? Three body segments, wings, six legs, antennae. Check! Wood louse? Hmmm … Sounds insect-y. But no! Once you take a look at it, you can see it’s only got one main body segment. The wood louse is actually a
crustacean like a crab or a shrimp. Slug? C’mon! That’s too easy: no legs, no wings, no exoskeleton. It’s just got that one blobby body with doodly-doos on its head. Definitely not an insect.3 See? Once you know the rules, you can get pretty good at this game.
Earlier I told you that insects are some of the most successful animals on the planet, and I want to circle back to that idea and tell you more. How do we measure success? One way is to look at the sheer volume of insects on our planet.
BY THE POUND
You probably learned this in the fourth grade, but it might be lodged deep in your gray matter … somewhere between that list of state capitals and that other list of American presidents. No worries. I can remind you. The animal kingdom is made up of six categories: mammals, amphibians, reptiles, birds, fish, and invertebrates. Invertebrates make up the largest chunk—more than 95% of the animal kingdom. Insects make up 71.1% of the invertebrate group.
Close to a million species of insects have been described and named. These are the ones we know about. Scientists have only been able to come up with rough estimates of the total number of insect species on Earth. They put that best guess somewhere between 3 million and 100 million species.
What does that mean in terms of the actual number of insects? It’s like a crap-ton. Obviously, “crap-ton” is not an objective number. I merely say that so you will know there are a lot. Some people have trouble processing big numbers. If it’s more than, say, five, I have trouble. But for the sake of transparency, I will give you the current estimate: At any time, it’s estimated that there are some 10 quintillion individual insects milling about.
What even is a quintillion? I had to look it up. It’s a 10 with 18 zeros after it. (Like that helps.) Here are a couple of other, more digestible ways to look at it. One out of every four animals on Earth is a type of beetle. For every human on Earth, there may be more than 450 kilograms (1,000 pounds) of termites—about as much as a full-grown cow. There are 1.4 billion insects per person on this planet. Like I was saying: crap-ton.
BY THE PLACE
You also probably know this already, but insects are everywhere. They live in every biome and every habitat on Earth. You can find them in wetlands, tundra, grasslands, oceans, deserts, tide pools, mountains, forests, prairies, rain forests, caves, swamps, in people’s homes, on people’s bodies, and in Antarctica. Antarctica always gets dissed. Like nothing goes on there or something. Tell that to Belgica antarctica, baby. It’s a flightless midge. It’s pretty hard to see as it’s no bigger than 6 millimeters (0.24 inches) long. Still, it’s the largest purely terrestrial animal native to the continent (as well as its only insect). Most animals can’t hack it there—it’s too freaking cold. Temperatures there cause cells to freeze and expand, and they can cause irreparable damage to most living things. Not so the midge! It’s capable of dehydrating its tissues to survive in temperatures down to 15° Celsius (5° Fahrenheit).
Belgica antarctica isn’t the only insect that can survive in extreme temperatures. Consider the Sahara Desert ant (Cataglyphis bicolor). This little dude scoots out of its burrow at the hottest part of the day, when the surface temperature of the sand is hitting about 70°C (158°F). What better time to dodge predators that can’t take the heat? The desert ant is looking to feast on the corpses of insects that have succumbed to the elements. How are these ants active in temperatures that would kill most living things? The desert ant has three tricks for its survival. First, it’s fast. It can hustle at 1 meter per second. Second, its long legs lift its body to a height that’s actually 6–7 degrees cooler than the ground. And third, it only stops moving when it’s in the shade. The Sahara Desert ant is bad to the bone.
But these tough little buggers don’t hold the record for heat. You’ve got your fire beetle to consider for that. While the desert ant lives in the desert and can’t help being around the heat, the fire beetle seeks the heat. It will fly 129 kilometers (80 miles) out of its way to cross paths with a raging forest fire.4 Why? Because these wood-boring beetles mate while a forest is still burning. Females then tuck their eggs under smoldering tree bark. The eggs hatch into larvae that nibble on what’s left of a tree for up to a year before tunneling their way out as adult beetles. It’s pretty clever, really. If they tried to breed in living trees, they’d be goners. The tree’s cell growth would squash them, or its resin would smother them.
You’ll find insects in high places. Some butterflies have been observed flying at altitudes up to 6,000 meters (almost 20,000 feet). Many insects make their home in the soil. You’ll find blind, cave-dwelling insects deep underground.
So we’ve covered cold places, hot places, high places, and low places. I think you get the picture: Insects are in a lot of places. But indulge me a bit further while I belabor the point. I need you to understand that insects really are everywhere. In California, there’s a maggot that lives in puddles of crude oil. It’s called the petroleum fly. I’m not making that up. Helaeomyia petrolei. It can submerge itself completely and swallow oil with no ill effects. It feeds on other unfortunate insects that fall into the puddles. It’s the only known insect species that develops in crude oil, a substance that is normally toxic to insects and, really, to every other living thing.
So, you know, that’s weird. But not nearly as weird as Orthohalarachne attenuata. That’s a type of mite that lives in a walrus’s nose. Don’t look it up. I’m warning you right now; it’s icky.
You looked it up, didn’t you? Well for Pete’s sake, what did you expect? I told you where it lived. Shouldn’t that have been enough for you? Did you read up about them too? Did you see the part where they can be sneezed up from one walrus to another? Good grief. And did you read about that one guy? At SeaWorld? How he saw the walruses spitting and snorting and then later reported an irritation in his eye? Yeah, you know what they found, don’t you?
And speaking of eyes … you know that they live in your eyelash roots, right? Not Orthohalarachne attenuata but Demodex folliculorum and Demodex brevis. Both of these types of mites are microscopic, so you can’t see them with the naked eye (especially when they are in your eye). They hang out there in your lashes and feast on dead skin cells because, you know, yum, yum!
I’ll give you one more example, just to make my point crystal clear. I’m guessing you’ve never really given any thought to moths and their ears, much less to moths and their great difficulty with ear mites. It’s an issue. Dicrocheles phalaenodectes.5 These mites break through the tympanic membrane of a poor moth’s ear and set up a small colony there. A moth needs its hearing to avoid predators—namely bats. Yet, once that membrane is broken, the moth goes deaf, which is why the mites only ever attack a moth in one ear. A moth with one functional ear is still able to avoid bats. I’m not sure how the mites instinctively know not to harm the other ear, but they do.
I’ve got a million more examples. You know I do. I told you: Insects are everywhere. Yet insects aren’t just successful because they outnumber us and because they are all over our planet.
They succeed because their bodies are wildly diverse, and over time, their bodies have adapted to many different environments. With people, one body type has to basically fit all of us. We’ve all got eyes, mouths, noses, and ears, and they all function in about the same way. Within the insect world, you see a great deal of variation.
MIGHTY MOUTH
Let’s start with the ol’ piehole. People can be bigmouthed or mealy-mouthed, but people generally have the same anatomical mouth. Insects have different kinds of mouths, and the type of mouth they have determines what and how they eat. If you’re an insect, you’re a chewer, a sucker, a sipper, or a sponger.
Chewing mouthparts are the most common. Think of grasshoppers and crickets. These insects use one pair of jaws (mandibles) to masticate. Such a great word, masticate. It means to bite, cut, tear, crush, and chew food. These jaws move side to side. If you’re a meat-eater, your mandibles are probably serrated and knifelike. If you stick to plants, your mandibles are probably broader and flatter. A second pair of jaws (maxillae) helps shove the food down your throat.
If you’re not a chewer, you might be a sucker. The best example of this, of course, is the mosquito. A mosquito’s piercing, sucking mouthparts work essentially like a hypodermic needle. Mosquitoes poke a hole in their victim and suck blood through the same opening. Insects like aphids and stink bugs aren’t interested in blood; they only want to suck plant juices. But their mouths work in the same way.
Suckers sometimes have special spit that’s loaded with digestive enzymes. It breaks down food for easier sucking. Enter the assassin bug. It impales then injects its prey with a venom-laced saliva. The saliva paralyzes the prey and liquefies its internal organs. Assassins are so efficient with their technique, they’re able to suck out more than 90% of the live weight of their victims.
A more polite way to eat is to sip your food. The siphoning mouthpart is a friendlier version of the piercing and sucking syringe. It’s the long, flexible straw, or proboscis, that butterflies and moths have. When not in use, the proboscis is curled up tightly beneath a butterfly’s head. The butterfly unfurls it to sip flower nectar.
A fly can’t chew, suck, or sip food. Instead, its mouthparts are equipped with a sponge. To make food soft enough to mop up, a fly has to barf on it first. That’s right. Flies puke up an enzyme-laden saliva that quickly dissolves food. Then the fly laps that mess up—barf and all—with its spongy mouthparts. Flies aren’t picky eaters, but they do like to taste what they’re feasting on first. They do that with special receptors in their feet.6 A fly’s feet are, in fact, about 10 million times more sensitive than a person’s tongue.
What’s interesting about these different mouthparts is that some insects have more than one type during their lives. As larvae, caterpillars are chewers, but when they become adults (butterflies), they develop proboscises and become sippers. Still others have mouthparts that are a combination of the types I’ve described. Bees have chewing mandibles, but they also suck liquid through a beak-like tongue. A few insects, like mayflies, have no functional mouthparts at all. They live only a few days with the sole purpose of mating and laying eggs, so they don’t need to eat.
CLEAN YOUR PLATE
What do insects eat? Whatever they want! Lots of insects eat plants, some insects eat other insects, and some even drink blood. As I mentioned, mayflies and some moths never eat. Their life cycles are too short for them to bother. Other insects—I’m looking at you, silkworm—cannot seem to step away from the table. A silkworm eats enough leaves to increase its weight more than 4,000 times in just 56 days.
The bulk of insects are herbivores. Some are picky eaters. The caterpillar of the monarch butterfly, for example, eats only milkweed leaves. It will starve to death if it cannot get these leaves, and once it has them, it’s capable of buzz sawing its way through an entire leaf in under four minutes.
Termites are destructive wood-eaters. They get into damp wood through the ground and bore elaborate tunnels as they dine. On its own, a single termite can’t do too much damage, but since they typically live in colonies of 50,000, they can be formidable. The largest subterranean termite colonies eat about 0.45 kilograms (a pound) of wood per day.
About a third of all insects are carnivores. I’m sure you can think of many examples of meat-eating predator insects: dragonflies, praying mantises, mosquitoes. I think carnivores stick in our minds more than herbivores because they’re so dramatic. They don’t just nibble their salads quietly while reading a good book in the corner. No, they tear heads off and let the juices run down their chins.
It’s no surprise praying mantises are killers. They look lethal. But a sweet-looking harlequin ladybug (Harmonia axyridis) may eat as many as 5,000 aphids during its life cycle. And not all insect prey is small. Giant water bugs (Lethocerus americanus), which may be as long as your hand, can kill tadpoles, minnows, and small frogs for food.
And I don’t mean to scare you, but driver ants (Dorylus laevigatus) go after extremely large prey. They are the only insect known to attack and devour people. You heard me. They will form columns 50 million strong and strike off across the countryside in search of food. If you are in the way, they will take you out. Now, to avoid causing a panic, I should say this happens rarely. But geez. It happens, people. It happens.
Still other insects, like the cockroach, will eat almost anything. These are omnivores. Cockroaches will dine on anything in your home: candy, cheese, meat, grease, fruits, vegetables, dog food. They’ll also consume leather, beer, glue, dried skin, books, paper, and human dander. The list is endless.
Ants are also omnivores. They tend to stick to living and dead plant matter, but they are foragers. A single ant can consume up to one-third of its body weight at a time. Yet each ant also contributes to the food supply of the entire colony. While one ant may only eat ounces per day, the entire colony might harvest pounds.
A cricket’s diet is very similar to a person’s diet. They are omnivores that eat fruit, meat, and vegetables. Their outdoor diet is a little different from ours: rotting leaves, rotting fruit, and insects. And they have a strange fondness for fabric.
Silverfish gravitate toward carbohydrates, particularly sugars and starches. They also eat shampoo, glue in books, paper, clothing, flour, and linens. You know, whatever you have on hand and can spare. They aren’t picky.
As always with insects, there are many, many stress-inducing examples I could give you of insects eating disturbing things. If you start to look into it, you quickly discover that there’s an uncomfortable amount of blood being sucked by insects. I thought so, anyway. On average, a female mosquito that’s ready to breed can drink between one and three times her own weight in blood.
Unlike mosquitoes, all bed bugs need a blood meal to survive. Research shows that bed bugs take between 5 and 10 minutes to fill themselves up. Okay, granted, bed bugs are small, and you might not even notice them feasting on you until well after the fact. But still. C’mon! Super gross.
THE BETTER TO HEAR YOU WITH
Many species of insects have exquisitely sensitive ears.7 You just rarely find their ears on their heads. Mosquitoes hear through their antennae. Crickets listen through their legs. Lacewings have ears on their wings. Cicadas and grasshoppers pick up sound through their abdomens. Parasitic flies hear through their necks. Among butterflies and moths, ears turn up everywhere, even on mouthparts.
In some species, ears are plentiful. The bladder grasshopper (from the family Pneumoridae) has six pairs of ears that line its abdomen. Yet the praying mantis has only one ear. And it happens to be in the middle of its chest.
This might seem all over the map to you—and rightfully so. But remember, insects are equipped with what they need to survive. We know sound is created by vibrations carried through the air. An insect’s ability to hear means it has one or more ways to perceive and interpret those vibrations. Ears capture, amplify, and filter sound. They keep track of predators, prey, and mates. And just as with insect mouths, insect ears come in a variety of designs.
Many hearing insects have a pair of organs that operate the way a drum does. A tight membrane stretches over an air-filled cavity. The membrane vibrates when it comes in contact with a sound wave. These tympanic organs are paired with a special organ that translates the sound into a nerve impulse. Butterflies and grasshoppers have these.
Some insects rely on a group of sensory cells on their antennae called the Johnston’s organ. Fruit flies rely on this to detect wing-beat frequencies of potential mates. Hawk moths rely on it to help stabilize their flight. A lot of caterpillars rely on small, stiff hairs called setae to sense sound vibrations.
Certain hawk moths have a remarkable structure called a labral pilifer in their mouths that enables them to hear ultrasonic sounds. This tiny, hairlike organ is believed to sense vibrations at certain frequencies such as those produced by echolocating bats. I have this image in my mind of the moth flying around with its mouth open, which might be useful to listen for bats as well as hoovering up any mosquitoes that get in the way of its flight path.
Not surprisingly, the type of ear an insect has relates to the quality of its hearing. Mosquito ears can hear specific frequencies as far away as 10 meters (32 feet); the many-eared bladder grasshopper can hear a kilometer or more away. Cricket ears pick up low frequencies; mantis and moth ears detect ultrasound. Katydids have broadband hearing.
ARE YOU HEARING THIS?
While we’re on the subject of hearing, can we talk more about sound for a minute? How do insects make sounds, and who is the loudest? I always thought cicadas held the record for being the loudest, but I’ve recently discovered that’s not quite right.
Insects have a number of ways they make sounds and, of course, different reasons for doing so. They might make a sound to scare off an attacker. They might make a sound to communicate with others of their own species—a mating call, for example, or a threat against an encroaching, competing male.
The most familiar sound-making method is called stridulation. Essentially, this is rubbing one body part against another. This is how grasshoppers, crickets, and some beetles make noise. Longhorn beetles scrape ridges on their heads against their bodies. It sounds a bit like rubbing two pieces of Styrofoam together. Grasshoppers have a series of small bumps on the inside of their hind legs. They rub the bumps against their front wings to make sound. With crickets, the bottom of the left wing is covered with toothlike ridges that make it rough. It’s known as the file. The top part of the right wing is called the scraper. When the cricket rubs its wings together, the file drags against the scraper and makes a chirping sound.
Only male crickets chirp, and they do so when they are looking for females. But the cricket’s chirp has long been admired by people as a pleasing sound. And it’s oddly useful. It can predict the temperature. No kidding. It’s a phenomenon known as Dolbear’s law. Good old Amos Dolbear, an American physicist and inventor, figured it out in 1897. Here’s the formula to convert cricket chirps to degrees Fahrenheit: Count the number of chirps in 14 seconds. Add 40. That’s your temperature.8 I couldn’t make that up.
But I digress. Katydids rub their wings together to make a call that sounds like “Katy did, Katy didn’t, Katy did, Katy didn’t.” Not sure what Katy is being accused of here, but it must be something pretty serious.
Cicadas9 usually get blamed for everything, but remember, they are active during the day. If you are hearing loud insect noises at night, you’re probably hearing katydids and crickets.
When they do “speak,” cicadas use the tymbal in the front part of their abdomens. It has a series of ribs that buckle one after the other when the cicada flexes its muscles. Every time a rib buckles, the rib produces a click. It’s sort of like how you make sound with a bendy straw—pushing and pulling the ribs of the straw together to make that click. If you could push, pull, push, pull, push, pull a bendy straw hundreds of times a second, the clicks would be so close together, it would sound like a buzz. That’s what’s happening with our friend the cicada. Much of the rest of their abdomen is hollow, so it acts as an amplifier for the sound.
Insects can also make sound by tapping some body part against something else. The deathwatch beetle (Xestobium rufovillosum) bangs its head on the wooden rafters of old buildings.10
Flies and bees buzz, using their flight muscles and wings to make the sound. You wouldn’t think they were trying to, but they actually are communicating when they do that. Any beekeeper who’s opened their hive and heard the “angry buzz” can attest to this.
And here’s something you might not know: Bees make a whooping noise when they are surprised. Honey bees can make a vibrational pulse with their wing muscles that is inaudible to humans but can be detected by accelerometers embedded in a hive. It took researchers a long time to figure out the meaning of this sound. At first they thought it was a way to vocalize “Stop!” Then they thought it might be a way to indicate “Food!” Researchers found that the sound often happens when a bee bumps into another bee near the accelerometer. They now believe that bees make that sound when they are surprised!
Another means of sound production is forcibly ejecting air or fluid from the body. Bombardier beetles make a popping sound when they eject a hot fluid from their backsides. The chemical, designed to ward off predators, vaporizes when it meets air.
Making sound by expelling air is said to be somewhat rare in insects. Scientists were stumped for years by the sounds walnut sphinx moth caterpillars made—loud squeaks and whistles. Caterpillars have eight pairs of openings (called spiracles) on their sides as part of their respiratory system. To discover which spiracles were causing the sounds, researchers systematically blocked each pair in turn. The enlarged openings of the eighth pair were responsible for the whistling sounds. The caterpillar forces the air out by contracting the front part of its body. This is a quick and easy way to make sound when threatened.
Yellow warblers and other foraging birds get spooked by the whistling and typically move away. In some instances, the caterpillar whistles mimic the alarm calls of birds like chickadees. So their whistles kept these birds away too. Madagascar hissing cockroaches use the same technique when they hiss.
This is all well and good, but I know you’re wondering the answer to my earlier question: Which insect is the loudest? It’s not the male cicada, as it turns out. Don’t get me wrong. When male cicadas get together to woo the ladies, the din is impressive. A choir of lovesick cicadas can out-voice a lawn mower at full bore, reaching volumes greater than 100 decibels.
No, the loudest insect is also the loudest animal on Earth. It’s the male water boatman. The water boatman (Micronecta scholtzi) is a tiny insect that lives at the bottom of freshwater ponds. It’s less than half a centimeter long but makes a noise of 99.2 decibels.11 By itself. For comparison, a freight train is about 90 decibels. How he makes this sound is somewhat unusual. He uses his penis.
The water boatman strikes his penis along the ridges on his abdomen. And despite the organ’s size—only the width of a human hair—this courtship song renders him the loudest animal on Earth, relative to his size. The sound doesn’t carry well from water to air. In fact, at least 99% of the sound is lost. Which is probably why you and I have never heard it.
I SPY
Insects and I have one thing in common: We’re nearsighted. They can’t see an object clearly if it’s more than 1 meter (3 feet) away. I can’t find my way out of a room without my contact lenses or glasses. Unlike insects, however, I don’t have compound eyes, which is just as well because that would be creepy.
Adult insects usually have two compound eyes.12 Each is made up of many individual lenses13 called facets. The eyes of some insects have as few as nine facets each; house fly eyes have 4,000 facets; and some dragonfly eyes have nearly 30,000.
Text copyright © 2022 by Brenna Maloney
Illustrations copyright © 2022 by Dave Mottram
