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The scientific study of insects is known as Entomology, it is also a branch of zoology.If you look at the past, the term insect was used in a very vague manner, and historically the definition of Entomology had included the study of terrestrial animals which are in other arthropod groups or phyla such as arachnids, myriapods, earthworms, land snails, and slugs. This is a wider meaning which is still encountered in informal use like seen in several of the other fields that are categorized with the term zoology. Entomology is said to be a taxon based category, which is any form of scientific study in which the main focus is on insects, and the related inquiries are by definition Entomology. Therefore we see entomology getting overlapped with a cross-section of topics that are as diverse as systematics, physiology, developmental biology, ecology, molecular genetics, behavior, biomechanics, biochemistry, robotics, agriculture, nutrition, forensic science, morphology, planetology, mathematics, anthropology, and more. 

If we consider there are over 1.3 million described species, among this, the insects account for more than two-thirds of all known organisms which date back to about 400 million years and are capable of having many kinds of interactions with humans and other forms of life on earth. Insects are everywhere, they come in many different shapes, sizes, and colors which allows them to live in almost every habitat. Insects have an important role in the food chain, without insects our lives would be very different. They pollinate many of our fruits, flowers, and vegetables. They are food for amphibians, reptiles, birds, and mammals and they feed on lots of living and dead things themselves using their different mouthparts and body shapes. 

Some insects are predators to hunt other animals, others are herbivores that eat plants and some live as parasites on or inside other animals. Others are scavengers and eat whatever they find in their environment. Lots of insects help to break down waste without them dead animals, dead plants, and poo would start to build up and make a real mess. Most insects are not pests, unfortunately, most people know about the few insects that cause problems than the others that benefit the natural world, insects help keep the balance of nature. Insects if suddenly morphed into large beings and decided to wage war on us, there is no doubt that humans would lose. 

We would simply be crushed by their sheer number. If we observe it is estimated that there are over 10 quintillion individual insects on earth. To compare with our population these invertebrates outnumber us by more than a billion to one. If we look carefully their astounding numbers are present at the species level as well. So far it has been reported that there are over 60,000 plus vertebrate species on the planet. If we see the class of insects we can be certain that there are a million known species and there are many others that have not been classified. In fact, these critters make up 75 % of all the animal population on earth. 

The abundance of the insects has come down to many things which together make them some of the most resilient, and adaptable creatures, starting with their impressive ability to breed. Many species can produce 100s of offspring within their lifetimes. In many cases, most offspring will die, but the ones that survive are more than enough to go into adulthood to reproduce. Offspring also mature more rapidly, so the cycle of reproduction resumes very quickly and can occur over and over again in a short period of time.Looking at all these numbers it means that looking at insects as a class they harbor a tremendous amount of genetic diversity. 

Considering the different species they will contain a wealth of genetic data that intern gives them the necessary adaptation which they will require to thrive in the range of environments across the planet. Even some of the most extreme environments are inbounds. If we see the flat bark beetles it can live at a -40 degrees Fahrenheit, the Sahara desert ants can venture out when the temperature of the surface exceeds 155 degrees and looking at some of the bumblebees which can survive in about 18,000 feet above sea level. Insects' exoskeleton also works as body armor, protecting insects from the outside world, and helping them cope with the habitat that other creatures can’t. Looking at their small size we quickly think this is a disadvantage which is something they will use to their benefit in many ways. It is because most species are so tiny in size, millions of insects are capable of inhabiting a small space and will be making use of all the available resources within it. This means they can occupy hundreds of different niches across the ecosystem. And if we consider some insects they survive by eating the stems, pollen, nectar, and even the roots of specific plants. There are others like wasps make use of live insects for their use, this is done by paralyzing the victims and laying their eggs inside. So in the case when the hatchlings will emerge, they can eat their way out thereby getting the necessary nourishment. 

Mosquitoes and biting flies feed on blood, taking advantage of this unusual resource to ensure their survival. And a whole bunch of other insects has built a niche around feces. The flies will lay their eggs there and some of the beetles will even build large balls out of the animal dung, which they will eat and use it for accommodating their eggs. Then there is the insect’s mighty power of metamorphosis, this trait not only transforms insects but also helps them maximize the available resources in an ecosystem. 

Consider butterflies, in their larval caterpillar form they chomp hungrily through the leaves at a rapid rate to help them grow and spin cocoons. But when they emerge as butterflies, these insects only feed on flower nectar. The term metamorphosis means the larvae and adults of one species, these will never be competing for the same type of resource, so we can say they can successfully share an ecological niche making sure they are not limiting their own success. The process we see is so efficient that an incredible 86 % of these insect species will undergo complete metamorphosis. We are big and they are small, so it is easy to forget that these critters are moving in their millions all around us all the time. Examine almost any patch of ground and you are to find them there. Their numbers are immense, and their success is unmatched. We may have to accept that it is insects, not us are the true conquerors of the planet.  



These are centipedes often we run into these into the garden. These have elongated flattened bodies, about 14 to 20 segments and on each segment, there is a pair of legs.


We run into a variety of crustaceans when we are eating, these are nothing but shrimps, crabs, etc. There are a lot of different crustaceans that we see in the yard too,  like salad bugs. Crustaceans have 5 to 7 pairs of legs with 2 body regions, along with 2 pairs of antennae. 


These are one among the larger and important groups among the beneficial and occasionally on pests as well are the arachnids. The arachnids, of course, are the spiders, ticks, and the mites. They are distinctive and have 4 pairs of legs, 2 body regions, and no antennae. We distinguish that from the big group that we talk about. Those are the insects.


Insects in the adult stage will always have the above-mentioned characters. They have 3 body regions: a head, thorax, and abdomen, which will show you 3 pairs of jointed legs, one pair of antennae, and wings. The wings may be of 1 pair or 2 pair and often those are the features used to characterize the insects. Now one thing that you need to understand about these definite things that they have is, sometimes these can be highly modified and what may look to you as head in the thorax, and abdomen on one insect may be very modified if you look at an insect-like scale or even a flea. They have special adaptations depending on their environment.

Cold Blooded 

  1. The other thing we need to understand about insects is that they are cold-blooded, which means the ambient temperature is the temperature of their body. So if they are in a cold environment they are cold, if they are in a hot area they are hot. 

  2. The temperature influences their rate of growth and activity and this is very important, as we start looking at some of our pests and we want to know how rapidly the pest problem is growing.

  3.  If you have a codling moth for example. We rely greatly on information with temperatures on how fast the insect is developing. To know how fast it is going to go from an egg to an adult moth or how many days it is going to be larvae and will do damage is very dependent on temperature.

In general, what we can say is that development is more rapid when temperatures are warm and that their rate of growth is more rapid when the temperatures are warm. But we need to keep in mind that there are extremes on both ends. So it gets too hot you are going to have problems or death.  


Here you have the abdomen, the large area thorax, and the head. If we look at a slightly more complicated view some more parts of the anatomy, covering the abdomen we have wings and they are actually attached up into the thorax. The wings can take a variety of different forms if we take an example of a beetle. They have very hardened 4 wings or front wings and then underneath there is a transparent wing that is much softer in texture. You can notice that if you see little ladybugs flying around, you will be able to see the hardshell wings then underneath are the fluttery transparent wings. Then on the head, you can see they have got the antennae, you can barely see the eyes to mouthparts. Then attach to the thorax we have the legs, so you are always going to see 3 legs on each side so it is 6 legs attached to the thorax. 

You don’t see legs in the abdomen ever, you will have to look at that very carefully that will tell youtube body parts. You can see the legs are segmented on the ladybug all these segments that we see are called Tarsem ears. They are the part of their little feet and in fact, we use those when we are keying out beetles. You can actually count the number of segments on them, in case of other insects you count the number of segments on their antennae or you will describe the antennae if it has got beads at the end of it. A beaded antenna doesn't have a large club, We have all seen some of the beetles that have very long antennae that go all the way over to the back of their body.

Insects Growth 

Some of the insects grow by shedding their outer skin, one thing that you need to know about the arthropods is that they have this hard outer skin and exoskeleton. The difference between vertebrates and invertebrates, we have a skeleton inside of us that holds up our frame whereas insects do not. They have this hard tight outer shell to them, it is obvious that if you have a hard outer shell it doesn't make it easy to grow. As the insects need to figure out a way to get out of that shell, what they do is mold and grow a little bit and then shed their skin. And with each molting, they typically change in both sizes and in appearance. All insects are benign as an egg, now you may not always see the egg. In the case of some of the insects, the eggs hatch within the female body, so they may be born as a little nymph and an aphid is a perfect example of that, but they all benign as an egg. We may have these 2 different types of metamorphosis and actually there is some gradual difference in some other once as well. 

With gradual metamorphosis, the insect starts out as an egg, and then you have the younger stages that very much look like the adult, but they are smaller. We call this immature stage as nymphs, the grasshoppers, termites, and true bugs all have this type of metamorphosis. The main difference that you will notice that besides being smaller is that they don’t have wings, only the adult stage has wings. But you can see as they go along, as they get a little bigger they start developing little wing pads, the bigger the wing pads are the more advanced the growth stage is in the instar, the closer they are to being an adult. 

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FAQs on Entomology

1. What is the State of Insects in a Complete Metamorphosis Stage?

Ans: In a complete metamorphosis the larvae are very different from the adult. The larvae are at the feeding stage, then you go to the pupil stage and the pupae can vary tremendously. Sometimes it can be hard and brown pupae or it could be in a silken cocoon, a lot of different characteristics. Then in the final molt stage, they become adults with wings. The pupal stage is generally inactive, but if you look very closely in pupae, it is a little bit warm outside. The adult stage tends to be the reproductive stage, very often with some of these the adults don’t even feed or not. Particularly aggressive feeders, for this it is a good example is a butterfly or moth. We know that caterpillars or larval stages will consume a lot of plant material. But in fact, the butterfly might just need a little bit of nectar and not be any kind of pest problem at all. Very different feeding between the different stages can be observed. An example of the insects that have complete metamorphosis are bees, moths, ants, beetles, mosquitoes, and flies, these tend to be the more advanced in the insects. 

2. What is Insect Development?

Ans: Here we can talk about mating which can only occur in an adult stage. So you are never going to see the larvae or worms mating. Typically the adults don’t have a lot of other functions they mate, they lay eggs and they die. Very often you will see a very short life span for the adult stage. Males are not always required in a lot of insect species, we don’t even see males or they are very uncommon they might not play much of a role at all in the propagation of the species. We talk about generations of insects, a generation is from an egg to an adult. So the length of time it takes to get from one to another as a generation, so there will be 4 generations in a year. This means you could have eggs and then adults lay eggs again and then you get another generation and so on. Another term that you will hear when we talk about insect development is overwintering. Obviously this has to survive through the winter and they don’t always do it at a certain stage. The cycle doesn’t begin with each year as an egg it is automatic in the spring and then you have larvae, a pupae then an adult. It can vary depending upon the species, the grape leaf skeleton is over the winters as pupae. It emerges in the springtime as an adult moth and there are quite a few insects that will overwinter in that stage. You can imagine a pupa is very resistant, a little bit tougher you can say not quite so delicate as some of those other stages so it would overwinter as the pupal stage and emerge as an adult in the springtime laying eggs then that generation starts. So sometimes you have a final generation kind of stops at the end of a season and then continues into the next year.            

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