Bugs- Defined

(link to pictures of common backyard bugs)

Page 1

The word bug is simply a synonym of the word Arthropod.  Arthropoda is the Latin name for the collection of organisms with jointed appendages and segmented exoskeletons.  These include insects, arachnids, millipedes, centipedes, and crustaceans.

The rest of this page is taken from:  Biology 4^th edition: Neil A. Campbell, University of California, Riverside.  The Benjamin/Cummings Publishing Company, Inc. 1996...I have paraphrased some parts, but others are directly from the book.

The estimated population of arthropods now living on the planet is 1 billion billion or 10^18.  Nearly 1 million arthropod species have been described- mostly insects.  2 out of every 3 organisms known are arthropods, which have established themselves in nearly every habitat of the biosphere.  Based on diversity, distribution, and sheer #’s, the Phylum arthropoda is the most successful group of animals to ever live.

 One characteristic of arthropods is their cuticle, or exoskeleton, which is made from layers of protein and chitin.  Some parts are soft and flexible, other hard like armor.  Protects the animal and provides points of attachment for muscles that move the appendages.  Strong and relatively impermeable to water.  =allowing evolutionary transition from water, onto land.  Shedding necessary to grow/molting…new cuticle is excreted= energetically expensive and temporarily vulnerable to predators.

Provides protection from desiccation.

 Sensory organs: eyes, olfactory receptors for smell, antennae for touch and smell.

 Open circulatory systems with hemolymph which is propelled by a heart through short arteries and then into spaces called sinuses surrounding tissues and organs.  Hemolymph reenters the arthropod heart through pores that are usually equipped with valves.  Body sinuses are collectively called the hemocoel. 

 Variety of gas exchange organs:

Aquatic species have gills with thin feathery extensions that place an extensive surface area in contact with surrounding water.  Terrestrial arth. Generally have internal surfaces specialized for gas exchange.   Tracheal systems, branched air ducts leading into the interior from pores in the cuticle.

 Evolved from annelids or shared a common ancestor, or maybe onychophorans= walking worms, and recent systematists using comparisons of ribosomal RNA and other macromolecules arge that onychophorans are true  (are unsegmented) arthropods and not annelids at all.

 Subphyla of Arthropoda:

Trilobitomorpha- extinct

Cheliceriformes- spiders, ticks, scorpions, sea spiders, eurypterids (sea scorpions, extinct)

Uniramia- insects, centipedes, millipedes

Crustacea- crabs, lobsters, shrimps, barnacles, isopods (?)

Two I will deal with= Cheliceriformes, Uniramia (maybe isopoda of crustacea).

Chelicerates- body= anterior cephalothorax, posterior abdomen.

Most anterior appendages= modified as fangs or pincers= chelicerae.

     Class arachnida: spiders, ticks, mites, scorpions, amblypids, solpugids, etc.

6 pairs of appendages

chelicerae (fangs or pincers)  pedipalps= sensing and feeding, and 4 pairs walking legs. Spiders pedipalps equipped with poison glands spill digestive juices into torn tissue which liquefies them before the spider feeds.

Most have simple eyes (single lens)

Book lungs gas exchange= most spiders= stacked plates contained in internal chamber.  Extensive surface area to exchange O2 and CO2 between hemolymph and air.

Spiders string webs of silk= a protein produced as a liquid by special abdominal glands.  Spun by organs called spinnerets into fibers that solidify.  Web is unique to species, and innate in knowing how to build.   Also used for escape droplines, cloth to cover eggs, and wrapping food.

     Uniramians & Crustacea

Jawlike mandibles

One or 2 pairs sensory antennae

Pair of compound eyes (multifaceted eyes with separate focusing elements)

     Uniramians

1 pair of antennae, unbranched appendages

believed to have evolved on land

     Crustacea

Two pairs antennae

Biramous appendages (branched)

Primarily aquatic, believed to have evolved in water

Uniramians and Chelicerates spread onto land during Devonian period, following plants.

Oldest fossil evidence of animals is millipedelike arth. About 450 mya.  Fossilized arach. Almost as old have been found.

Millipedes- 2 pairs/segment, eat decaying leaves and other plant matter, among earliest animals on land, living on mosses and prim. Vascular plants. 

Centipedes- terrestrial carnivores, head has antennae, and 3 pairs of appendages modified as mouthparts, including jaw-like mandibles.  1 pair legs/segment.  Poison claws on anterior-most trunk segment to paralyze prey and defense.

Insecta-

Outnumber all other forms of life combined.  Go back to Devonian period.  Flight evolved during carboniferous and Permian periods.  Mouthparts specialized for feeding on gymnosperms and other Carboniferous plants spurred adaptive radiation.

 Insect evolution paralleled flowering plant evolutionary radiation about 65 mya.  Co-evolution with angiosperms likely.

 One or two pairs of wings contribute to success of class insecta…are extensions of cuticle, not appendages.  …not sacrificed appendages like in other animals.

 Dragonflies among first insects to fly- coordinated wings.  Fossilized specimens have 2 ft. wingspans!

Bees and wasps hook wings together to fly, as single pair…similar to butterflies.

Beetles- posterior wings used for flight, anterior are simply covers.

Internal anatomy-

Digestive tract tube pinched in several regions for separate breakdown of food, absorption of nutrients.

Open circulatory system

Metabolic wastes removed from hemolymph by unique excretory organs called Malpighian tubules, which are outpockets of the gut.

Gas exchange via tracheal system of branched, chitin-lined tubes that infiltrate the body and carry oxygen directly to cells.  Opens to outside through spiracles, pores that can open and close to regulate air flow and limit water loss.

Central nervous system= pair of ventral nerve cords with several segmental ganglia.  Two cords meet in the head, where the ganglia of several anterior segments are fused into dorsal brain, close to antennae, eyes, and other sense organs on head.   Behaviors seem innate, not thought.

Incomplete & complete metamorphosis

Complete- bright colors= butterflies mating, sound= crickets, odors= moths…female lays ova on food source

Fertilization and reproduction

Females spermatheca can hold sperm and usually fertilize more than one batch of eggs.  Many insects mate only 1 X in a lifetime.

Malaria, sleeping sickness, pollination, crop loss

US spends billions on pesticides/yr.

Crustaceans

(Terrestrial- Sow bugs & pill bugs

Live mostly in moist soil and damp places)

 40K species

lobsters and crayfish have 19 appendage pairs.

2 pairs of antennae

3 or more pairs mouthparts

walking legs on thorax

have appendages on abdomen, unlike insects

lost appendages can be regenerated

small crustaceans exchange gases across thin areas of cuticle

larger forms have gills.

Nitrogenous wastes excreted by diffusion through thin areas of cuticle…pair of glands regulates salt balance of hemolymph.

Lobster uses specialized appendages to transfer sperm to female’s reproductive pore.

Most aquatic go through one or more swimming larval stages.

Lobsters, crayfish, crabs, shrimp=decapods

^cuticle hardened by calcium carbonate

carapace covers thorax dorsally.

Copepods are very numerous and include plankton which includes larvae of larger animals. 

Krill are planktonic organisms that whales eat.

Barnacles are sessile (fixed to one place), with parts of cuticles hardened into shells by calcium carbonate. Use appendages to strain food from the water.

To Taxonomy, Page 2>

<back to Table of Contents