Phylum: Arthropods, Class: Insecta


Kingdom: Animalia

Phylum: Arthropoda

Class: Insecta

Phylum ARTHROPODA: Insects, Spiders, Scorpions, Crabs, Shrimp

General characteristics of phylum:

- most successful animal phylum with more than 1,000,000 discovered species
- sub divided into 29 orders

- found in nearly every habitat

- segmented with exoskeleton and jointed legs


Subphylum UNIRAMIA: Insects, Centipedes, Millipedes

General characteristics of Insects (class):

-          Insects are the most successful life form on the planet: they make up more than half of all living things on Earth

-          Some experts suggest that there are more than 10 million insects

-          Divided into 29 orders

-          Often occur in incredibly large numbers: on an area with a size of a football field, more than 400,000,000 insect species were found

-          Largest order: beetle (125 families, one in every four animal species on this planet is a beetle)

-          They are ubiquitous: you can find them everywhere on land, but only very few have colonized the sea (Marine Flies)

-          Brine Flies: some of the most adventurous insects, which can be found in the strangest places

Basic Anatomy:

-          Chitinous (hard) exoskeleton, no bones or a skeleton

-          Three-part body: head, thorax, abdomen

-          Three pairs of jointed legs (6 legs)

-          Compound eyes which contain several thousand lenses leading to a larger field  of vision

-          Two antenna

-          One of the most diverse group of animals on Earth:

o   Represent more than half of all known living organisms

o   Found in almost all environments

o   Number of extant species of class insecta: 6-10 million

o   Represent over 90% of differing life forms on Earth

-          Representatives: fleas, moths, flies, wasps, mosquitoes, grasshopper, beetles, cockroaches, termites, butterflies, ants

-          Are mostly solitary, but some insects (bees, ants, termites) are social and live in large, well-organized colonies

-          Communication occurs in many different ways: males can sense pheromones of female moths over distances of many kilometers (moths), sounds to attract mates (crickets)




Basic Anatomy cont.:

-          Cuticle: outer layer, made up of epicutle (thin, waxy, water resistant, no chitin) and procuticle (chitinous, thicker, two layers)

-          Three-part body:

o   A. head: pair of sensory antenna, pair of compound eyes, and if present, one to three simple eyes and three sets of modified appendages that form the mouth part

o   B. thorax: six segmented legs which are used for several things such as running or swimming, and if present, two or four wings

o   C.  abdomen: consists of eleven segments, contains most of the digestive, respiratory, excretory and reproductive internal structures

-          Only invertebrates who can fly, which is very important for their success: muscles are connected to exoskeletons and are able to contract multiple times for each nerve impulse


Nervous System:

-          Brain and ventral nerve cord

-          Cells that detect and transmit sensations of pain (Nociceptors), but not proven that insects feel pain consciously

Digestive System:

-          Some insects drink their food, others chew
    most insects are herbivores, some are carnivores and some feed from decaying material

-          Same function as in humans

-          Most food is ingested in form of macromolecules, proteins, fats, polysaccharides, and nucleic acids and are broken down into smaller parts like amino acids and simple sugars (digestion)

-          Main structure: alimentary canal (long enclosed tube running lengthwise through body) directing food from mouth to anus

-          Insects also have paired salivary glands and salivary reservoirs found in the thorax  

-          Some have extra-oral digestion expelling digestive enzymes onto their food to break it down (flies). This has the advantage that insects can extract more nutrients from the food

-           Almost all of the digestion takes place in the gut, which is divided into

o   A. Foregut

o   B. Midgut

o   C. Hindgut

Respiration and Circulation:

-          Insects do not have lungs! They breath passively through their “Spiracles” (openings in the side of their cuticle). Oxygen is delivered directly via trachea (series of smaller and smaller pipes) to the tissues that need it

-          Since diffusion of gases is only effective over small distances, insects are relatively small

-          Different patterns of gas exchange shown by different types of insects: continuous/ diffusive ventilation, discontinuous gas exchange, some insects have gills (extract oxygen dissolved in water)


Reproduction and Development:
                -        Growth is constrained by inelastic exoskeleton
                   Mainly sexual reproduction between males and females
                -    4 different life stages (instars): eggs, larva, pupa and adult
                -    Complete vs. incomplete metamorphosis
                -    Most hatch from eggs, which are laid in a sheltered place or produced internally
 -     Development involves a series of periodic molts, where new, soft exoskeleton is formed below

                                    Source:  Source:  

Humans and Insects:

-          Some insects represent pests (crop damage)

-          Some fed on blood of humans and livestock

-          Some are capable of transmitting diseases (Malaria)

-          Many are ecologically beneficial: termites recycle dead trees which keeps forests healthy

-          Few provide direct economic benefit (silkworms, bees)

-          In general: insects are more beneficial for us as harmful!



Fun Facts:

-          Many insects have the nose on their antennas and the ears on their legs

-          They can communicate in the infra- and ultrasound spectra

-          Some can send out light

-          Largest insect: Acteon Beetle from South America, males can become 9 cm or longer in length, 5 cm long and 4 cm thick; some beetles can become as long as 16 cm

-          Heaviest insect: gravid female Deinacrida heteracantha can weigh as much as 70 grams


Fun Facts Bees:

-          Bees fly an average of 13-15 mph

-          Honeybees visit about 2 million flowers to make one pound of honey and fly fifty-five thousand miles

-      During honey production periods, a bee's life span is about 6 weeks

-      Honey bees are the only insects that produce food for humans

-      One single bee usually visits between 50-1000 flowers a day, but can visit up to several thousand

Fun Facts Ants:

-          Very social animals living in colonies with a minimum of about 50 individuals

-          Supercolony of Formica yessensis was found to have had more 1,080,000 queens and 306,000 workers in 45,000 interconnected nests

-          10% of animal biomass of the world is ants and 10% is made up of termites: social insects make up about 20% of the total animal biomass of this planet



Fossil Findings:

-          Insects of enormous size have been found from the Paleozoic Era (542-251 million years ago) such as dragonflies with wingspans of 55-70 cm

-          Most diverse insect groups probably coevolved with flowering plants


Reasons for their success:

-  incredible mixture of flexibility and strength of the integument (hard exoskeleton): allows insects their freedom of movement without loss of defence and protection. It is made up of three parts, the most visible of which is the outer 'cuticle' and its attendant bristles and hairs, below this are the 'epidermis' and the 'basement membrane'
- only invertebrates that have the ability to fly
- high diversity of habitats (from deserts to polar regions)
- very high adaptability