8 Characteristics That Define Insects

A female Asian Tiger Mosquito enjoying a blood meal. The light-colored needle you see drilling through this poor soul’s skin is actually six super-thin needles, each with a different job to perform. The bent, gray tube is a sheath that straightens to cover the needles between meals. Photo courtesy of James Gathany of the Centers for Disease Control and Prevention (CDC) at Wiki Commons.

I can actually feel the bite of this mosquito. Mosquitos are the bane of summertime existence in coastal Texas, as they increasingly are in other areas due to climate change and urbanization. Did you know only females bite and feed on blood, which they need to nourish their eggs? That’s how we know the mosquito above is female. We also know she just started her meal, because her abdomen would be engorged otherwise. See the photo below to see what I mean. If you’re wondering, both males and females feed on nectar, plant juices, and honeydew, which is the sugary secretion of tiny insects like aphids.

The female Asian Tiger Mosquito plump with blood. She’s attracted to perspiration, warmth, body odor, and carbon dioxide, so people in hot, humid areas are doomed. Photo from James Gathany at Wiki Commons.

Mosquitos don’t bug just humans; they bite other animals, including reptiles and birds. They pick up diseases from infected victims and pass them on.

Researching mosquitos got me thinking about other insects. Honestly, I’d forgotten a few things over the years, so I decided to review their basic characteristics.

The natural place to start is with their segmented bodies. In fact, the word “insect” derives from Latin and Greek words meaning “with a notched or divided body.” Insect bodies divide into three parts: the abdomen, thorax, and head.

This Honeybee exhibits a well-defined three -part body. Photo courtesy Michael Siebert on Pixabay.

Besides the digestive tract, an insect’s abdomen includes its reproductive organs, and respiratory and circulatory systems. Legs and wings attach to the thorax. The head comprises the eyes, antennae, and mouth. Insects with stingers, like bees and wasps, carry them at the rear of their abdomens. With the mosquito, the head delivers all the damage. That’s where we find the proboscis, which contains a complex system of needles that pierces the victim’s skin, sucks out the blood, and leaves behind hitch-hiking viruses like yellow fever, malaria, and west nile.

As support and protection, a rigid exoskeleton encases an insect’s body. If you’ve ever plucked the discarded shell of a Cicada from a branch, you’ve been up close and personal with an exoskeleton. Entomologists call these remains “exuviae.” Cicadas live most their lives as underground “nymphs”–juveniles that look like adults except for the wings. When they finally emerge from the ground as adults, they shed their outgrown exoskeletons. The process is called moulting, and almost all insects do it at least once in their lives.

This adult Cicada is drying off after moulting, and it’s not the first to do so in this spot. Some pesticides like Neem Oil disrupt moulting by confusing an insect’s brain function; larva forget to escape their outgrown exoskeletons and suffocate. Image by vividsoup from Pixabay.

The American Cockroach, an accomplished sprinter. Image by pichai25 from Pixabay.

Adult insects have three pairs of jointed legs attached to the thorax. Just as different types of insects have their own unique abilities, so do their legs. Cursorial legs on cockroaches are best for running, while the Saltatorial legs of grasshoppers excel at jumping. Aquatic insects like diving beetles rely on Natatorial legs to paddle efficiently. Fossorial legs help Mole Crickets burrow through dirt. Finally, predators like the Praying Mantis wield Raptorial legs to grip other insects.

We clearly see six legs on this Four Spotted Dragonfly. The raptorial pair in front grasps prey, which includes mosquitos. Photo thanks to Georg Wietschorke at Pixabay.

All insects have a pair of antennae, which they use to sense smell. Olfaction helps them to avoid predators, to find food or a mate, or to locate a place to lay their eggs. With at least twice the odor receptors of other insects, ants top the insect mound with their ability to smell. (In another win, ants are the most numerous insects in the world, with 10 billion billion individuals. That’s a one with 18 zeros.)

A Fire Ant and its two antennae, photo courtesy skeeze from Pixabay Their highly developed sense of smell enables ants to form complex colonies. During Hurricane Harvey in 2017, fire ants formed rafts to float atop flood waters, with rafts containing as many as 100,000 ants.

Most insects have compound eyes, which absorb light through thousands of tiny lenses, each focused in a slightly different direction. While the single, large lens in the human eye produces much sharper images, the compound eye enables a far greater viewing angle. The insect sees much more of its surroundings at a single glance. What this means practically is that we see a fly clearly enough to swipe at it, but the fly has already seen our hand, even if coming from almost directly behind it, and swerved to safety.

The compound eyes of a Housefly, courtesy of aixklusiv at Pixabay. It’s estimated that while we see 100 time as clearly as the most eagle-eyed insect, an actual eagle sees two to three time as clearly as we do.

All insects hatch from eggs, although in a few rare cases the female retains the eggs in her body until they hatch. Once hatched, most insects don’t emerge as tiny versions of their parents (like reptiles, birds, and mammals), but as larvae or young nymphs. From there they progress through additional life stages, a process known as Metamorphosis.

For paper wasps, the first three stages take place inside the nest, with adults emerging fully formed.

Red Paper Wasps, so named because of the fibrous nature of their nests. Image from Kevin McIver on Pixabay.

Houseflies search for warm, moist, and dark places to lay their eggs. A pile of fresh cow manure is ideal. Like butterflies, Houseflies develop through egg, larva, and pupa stages before emerging as adults.

A Blue Bottle Fly. Note the diminutive second set of wings, called “halteres,” just above the middle leg. Photo by Paul Hampshire on Pixabay.

Nearly all insects have wings and fly, with most having two pairs of functional wings. Flies and mosquitoes are exceptions. They have halteres, club-like organs that act as vibrating gyroscopes to maintain stable flight. There are over 800 types of flying insects.

Green Darners are large dragonflies and can grow to five inches long, but usually stay around three. They’ll eat any insects smaller than themselves and usually during flight. Photo courtesy of Santa3 at Pixabay.

Many insects contribute to pollination, with bees and butterflies being the most prominent. As they buzz and float from flower to flower in search of nectar, they transfer sticky grains of pollen from the anther of a flower to the stigma, thus fertilizing the plant so it can reproduce. But bees and butterflies aren’t the only pollinators. Wasps, flies, mosquitoes, beetles, and even ants pollinate.

This hungry bee is an unsuspecting pollinator. Photo courtesy Myriam Zilles on Pixabay.

I hope your knowledge of insects is now back to where it once was. I’ve enjoyed the review.

Works Cited

“Aedes Albopictus (Asian Tiger Mosquito).” Wikipedia.

“Calliphora Vomitoria (Blue Bottle Fly).” Wikipedia.

“Exoskeleton.” Wikipedia.

“Four-spotted chaser (dragonfly).” Wikipedia.

“Four-spotted chase.” British Dragonfly Society.

“Friday 5: Five Types of Insect Legs.” The Dragonfly Woman. 10 Dec 2010.

“Green Darner Dragonflies.” Columbus Audubon.

Hadley, Debbie. “7 Insect Pollinators That Aren’t Bees or Butterflies.” ThoughtCo. 20 July 2019.

“How to Identify Different Types of Bees.” Treehugger.

“Insect.” Wikipedia.

“Insect Olfaction.” Wikipedia.

“Metamorphosis (Insects).” Wikipedia.

“Mosquito.” Field Guide to Common Texas Insects: Texas A&M Agrilife Extension.

Quiros, Gabriella. “Watch: Mosquitoes Use 6 Needles to Suck Your Blood.” NPR. 7 June 2016.

Salisbury, David. “Ants Have an Exceptionally High-def Sense of Smell.” Research News at Vanderbilt. 10 Sep 2012.

“What is Pollination?” U.S. Forest Service.

Categories: animals

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