The Mechanics of Insects

Pests, Plagues & PoliticsLecture 2

The “bug suspension system”

Gary Larson’s finest effort!!!

“Nik! The fireflies across the street - I think they’re mooning us!”

Key points:

Mechanics of Insects

• The importance of being small• Advantages of an exoskeleton• The Insect Body Plan• Basics of insect vision• Mechanics of flight• Insect growth and development - metamorphosis

Science & the Human Ego• Copernicus removed us from the center of the solar system.• Darwin displaced us from near-angelic status.• Edwin Hubble informed us that the Milky Way is an undistinguished

galaxy in a nondescript corner of the universe• Human Genome Project estimates that the human genome

contains a mere 33,000 genes (not 100K)– Mouse = 28,00– Fruit fly = 23,000

FYI

“Something in the insect seems to be alien to the habits, morals and psychology of this world, as if it had come from some other planet, more monstrous, more energetic, more insensate, more atrocious, more infernal than our own.” ~ Maurice Maeterlinck

The MECHANICS of INSECTS• What is the “plan” natural selection gave

for such a successful group of animals??A small creature!!

• Why are there so many small animals in the world??

• < 0.01” 20,000 species• 0.01” to 0.1” 220,000 species• 0.1” to 1.0” 600,000 species {70%}• 1.0” to 10” 20,000 species• 10” to 100” 1,500 species• > 100” 10 species

Answer:

• The availability of “niches”

“The maximum number of niches available, then, is for animals whose size is somewhere in between tiny water dwellers.. and the more sizable land dwelling mammals such as birds & reptiles.”

“It is the size range most suitable to the physiology & anatomical features of INSECTS.” {Harold Morowitz 1982}

Why no GIANT insects?

• SA/v – surface area to volume ratio– Volume increases as the cube of length– Surface area increases as the square of length

• Insects have a very high surface area to volume!! {remember, bugs are small}

Small s/v ratio High s/v ratio

Why no giant insects, cont.

• Most insects FLY– Flight is dependent upon surface area of wing in

relation to the weight to be lifted.– The weight of a very large insect would increase by the

cube, while the wing surface area could only increase by the square of the length!!

– Insect anatomy “….is largely a struggle to increase surface area in proportion to volume.”• J.B.S. Haldane

- This is a problem for water loss/retention…

How to “keep your water”

• Surround yourself with a water-tight envelope• A combined epidermis (skin) & skeleton

An EXOSKELETON

epicuticle

exocuticle

endocuticle

multi-layered, laminated

Exoskeleton• Composition– A LAMINATED structure largely composed of CHITIN {a

nitrogenous polysaccharide}– Chitin is hardened by a tanning process involving the

protein sclerotin.• Advantages– Defense: against predators & pathogens– Water loss control– Lightweight & strong {for muscle attachment}

How to breathe??

How to breathe??• Through your “skin” with tubes & ports• (called Tracheae & Spiracles)

“blood” flow

Insect Body Plan• Segmentation– a linear repetition– Metamerism

• Insect Scheme– Three major body divisions

HEADTHORAX

ABDOMEN

Insect Body Plan

SIX Legs

– Walking & other functions• swimming, eating, mating

– Segmented/Jointed Linkage

Question to Abraham Lincoln: “How long should a man’s legs be?”Answer: “Long enough to reach the ground.”

The “Bug Walk”

FYI

The bug suspension system

FYI

Vision• So foreign, those hemispherical, multi-faceted eyes.• The ultimate “insect” stereotype.• The COMPOUND EYE– Formed from individual visual units known as ommatidia.

FYI

The hairy eyeball:

Worker Honey Bee

[the front end]

FYI

Vision

• Color– Trichromatic, often shifted to the UV• spectral coverage 300 nm to 680 nm

–Polarized {at least for some groups}–Visual acuity is low {relative to humans}–A MOSAIC image is produced

Human’s View

Bug (bee) View

FLIGHT• Insect wings are NOT modified limbs.– {as is the case with birds, bats & pterodactyls}

• Arose as independent structures– thought to be derived from a single evolutionary event.

• A network of braces (veins) that enclose regions of thin cuticle (membrane/exoskeleton)

• Powered by muscles in the thorax

VEIN

MEMBRANE

Insect Flight Muscles

• Myogenic• Asynchronous• Striated• Power Output– 3.84 hp per kilogram (honey bee)[the = of you having a 288 hp engine]– 30 times greater than the human leg muscle

• Requires a heavy energy input to power flight– 1,300 to 2,000 kilocalories per kg– highest of any known animal tissue

FYI

Winged Flight

• Number of wings–0 - the apterous, mostly “ancient” insect

groups–2 (one pair) - the order Diptera• di = 2 - ptera = wings• the stereotypic true flies.

–4 (two pairs) - numerous orders

Growth & Development

• Not like vertebrates• Accomplished through molding/shedding

of the exoskeleton– A process called Metamorphosis

(many/multiple shapes/forms)

• Stages between molts known as INSTARS

METAMORPHOSIS

Two General Types

1) incomplete or direct = HEMIMETABOLOUS- immature stages called nymphs- nymph similar to adult in appearance, food and habitat- grasshoppers are the classic example

2) complete or indirect = HOLOMETABOLOUS- the adult (imago) and the immature stage (larva) differ dramatically, and not just in physical form, but also in food choice and habitat- the egg-larva-pupa-adult paradigm

METAMORPHOSIS - incomplete

Hemimetabolous• egg to nymph to adult

METAMORPHOSIS - complete

Holometabolousegg – larva – pupa - adult

Life Cycle of a ButterflyVideo – click here

Life cycle of a fruit fly

Linnaeus & MetamorphosisEtymologies: larvae = “mask” imago = the “image” or essential form

Metamorphosis as PROGRESS TOWARDS FULFILLMENTApplied to the human model: children are to be viewed as underdeveloped, imperfect adults - adulthood is the termination - childhood an upward (linear) path

- 17th and 18th century zoologists loved this especially as a metaphor for the good Christian Life.

Butterfly: larva (caterpillar) = the imperfect prison of the body pupa = death & entombment; adult = winged freedom and resurrection….A lot a nonsense!!!

What do you think???

FYI

Key points:

Mechanics of Insects

• The importance of being small• Advantages of an exoskeleton• The Insect Body Plan• Basics of insect vision• Mechanics of flight• Insect growth and development - metamorphosis

Glossary

Metamerism – n. a linear series of body segments fundamentally similar in structure, though not all such structures are entirely alike in any single life form because some of them perform special functions. In animals, metameric segments are referred to as somites or metameres.

Etymology – n. the study of the history of words, their origins, and how their form and meaning have changed over time. By an extension, the term "etymology (of a word)" means the origin of a particular word.

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