All insects are part of the taxonomical phylum Arthropoda, and they are collectively referred to as arthropods. It is common to see this name misspelled as “anthropod,” but this is not the correct term. They can be found in nearly every environment on the planet, and they currently account for over half of all known living organisms in the world. They have undergone many cycles of evolution depending on the resources available to them. With over one million described species currently living, and millions more estimated to exist, insects greatly outnumber all other animals.
In general, this classification of creatures is referred to as Insecta. In some cases, the terms “Ectognatha” and “Entomida” may be used instead, but these three labels are synonymous and may be used interchangeably. For simplicity, this guide will always use the classification Insecta.
The name Insecta is derived from the Latin word “insectum,” which means “divided body” or “cut into sections.”
The Four Major Insect Characteristics Listed
Insects are one of the most diverse groups on the planet, and their evolution throughout history is astounding. However, in order to be considered a member of the class Insecta, animals must meet a certain number of criteria. In fact, many people are surprised to learn that many of the bugs that are commonly believed to be insects are technically not a part of the Insecta class.
1. Insects have three distinct body segments.
One of the most well-known defining characteristics of insects is the division of their bodies into three sections: head, thorax and abdomen.
The head features a single pair of antennae and a pair of either simple or compound eyes. This is also where the mouth is located, but the type of mouth is dependent on the type of insect. Mouth variation is one of the main factors used to classify insects. The thorax is the midsection, and this is where the legs and wings are attached. The abdomen houses the digestive and reproductive organs, and it is also where the stinger is located if the insect has one.
2. Insects have six legs.
Unlike other members of the larger phylum Arthropoda that class Insecta belongs to, true insects only have six legs. Arachnids are often mistaken for insects, but they have eight legs. All insects have three pairs of jointed legs that are attached to the thorax of the body.
3. Insects have an exoskeleton.
Insects are classified as invertebrates, which means they have no internal spinal column to provide structure and protection. Instead, they have what is known as an exoskeleton, which literally means “outer skeleton.” These external skeletons are made from a tough, inflexible material called chitin, and they provide the support and protection that would typically come from an internal skeleton.
4. Insects hatch from eggs.
Almost every known species of insect hatches from an egg. For insects, fertilization and development occur inside of the egg, and the eggs of most species are specially designed to withstand harsh weather conditions such as droughts.
Insect Class Exceptions
As with most classification systems, there are a few exceptions to the general rules that govern which species are included in class Insecta.
- Certain species do not lay eggs.
The majority of insects lay eggs that develop and hatch outside of the mother. However, there are a handful of insect species that reproduce via different methods, such as those listed below.
- Juvenile aphids, tsetse flies and certain cockroaches are ovoviviparous, which means that the eggs develop inside of the mother and hatch as soon as they are laid.
- Other cockroach species are viviparous, so the young gestate inside of the mother and are born alive.
- Some insect species display polyembrony, which means that one fertilized egg divides into many separate embryos.
- A few species are bioluminescent.
A small number of insects, such as fireflies, are able to generate light that can be used for mating or luring prey.
- A select few insects are long-lived.
In general, insects live short lives. While most insects may only live a few days or weeks, the egg-laying queens of some ant, bee and wasp species can live for many decades.
The Life Cycle of Insects
The life cycles of insects are divided into two basic groups: complete and incomplete metamorphosis. Each life cycle has its advantages and disadvantages in terms of evolution.
Complete Metamorphosis Steps Listed
Complete metamorphosis happens in four distinct stages.
- Egg: The female lays fertilized eggs that hatch after a given span of time.
- Larva: This is the growth phase. Larvae spend nearly all of their time eating in order to prepare for their final transformation.
- Pupa: The pupa is the transformation phase. The insect is contained within a hard shell called a chrysalis, and all of the internal organs are broken down into a kind of “soup.” This liquefaction allows the adult body to form.
- Adult: Once the reorganization of the pupa stage is complete, the chrysalis will split open and the fully formed adult emerges.
Incomplete Metamorphosis Steps Listed
Incomplete metamorphosis occurs in lesser-developed insects and happens in only three stages.
- Egg: As with the insects that undergo complete metamorphosis, eggs are laid by the female and hatch into young.
- Nymph: In this stage, the young look like miniature versions of adults, but they cannot reproduce. Wings develop during this stage rather than the pupal stage. Nymphs will undergo a series of molts in order to shed their inflexible exoskeletons as they grow.
- Adult: After a nymph’s final molt, it will have fully developed wings and the ability to reproduce.
Insects FAQs (Frequently Asked Questions)
What are the general features of insects?
Insects are all members of the group Arthropoda, which makes them arthropods. It is not uncommon to see this group mislabeled as “anthropods,” but the correct spelling is “arthropod.”
In general, insects share all of the following common features:
- An exoskeleton
- A pair of wings
- A segmented body
- Six segmented legs
- One pair of compound eyes
- One pair of antennae
What is an insect?
An insect is an arthropod that has distinctive characteristics such as three body segments, six jointed legs, one pair of antennae, one pair of compound eyes and an exoskeleton.
How many legs does an insect have?
All true members of class Insecta have three pairs of jointed legs.
What is the life cycle of an insect?
Depending on the species, insects experience either complete or incomplete metamorphosis. The stages of complete metamorphosis are egg, larva, pupa and adult. The stages of incomplete metamorphosis are egg, nymph and adult. Insects generally have short life cycles that may last a few days or a few weeks.
Are spiders insects?
Spiders are not a part of the class Insecta, but they are part of the larger group of arthropods. Some people incorrectly label this group as “anthropods,” but this is not quite right. Because they have four pairs of legs instead of three and only two distinct body segments, they belong to the class Arachnida.