1. The Little Creatures Who Rule the World
Amazing Arthropods!
The Little Creatures Who Rule the World

2. General Characteristics
Segmented bodies
Jointed appendages
Exoskeleton
Highly cephalized
Open circulatory system

3. Exoskeleton - advantages
Enables great strength (internal muscle attachment).
Waterproof - enables life on land.
Protective armor.

4. Exoskeleton - limitations
Must be molted (shed) in order to grow. Recently molted animals are vulnerable.
Heavy - limits overall size.

5. Cephalization Specialized mouthparts - sensory, food-handling.
Antennae - sense chemicals, vibrations.
Compound eyes - many individual units, each w/own lens, good at detecting motion, color.
Simple eyes - detect light intensity.

6. Arthropods: Class Crustacea
Crabs, lobster, shrimp, barnacles, etc.
Mostly aquatic
Two body divisions, cephalothorax & abdomen

7. Crayfish Anatomy Most crustaceans are scavengers or predators.
Chelipeds – strong claws for grasping & cutting or tearing
4 prs. Walking legs
Swimmerets – on abdomen, move water over gills & or eggs.
Crayfish Anatomy

8. Internal Anatomy & Senses
Green glands – excretory organs in head
Open circulatory system
Gills – attached to each walking leg, moves H2O over them as it walks.
Ventral nerve cord
Compound eyes – many lenses working together, good for detecting movement.
Statocysts – detect orientation (up & down) as gravity pulls on grains of calcium carbonate inside.
Males have specialized swimmerets for sperm transfer – internal fertilization.
Antennae –
touch,
chemicals

9. Arthropods: Class Arachnida
Spiders, scorpions, mites, ticks
Mostly terrestrial
Two body divisions, cephalothorax & abdomen
4 prs. Walking legs
Carnivorous or parasitic

10. Spider Anatomy Book lungs for respiration – large surface area.
Spinnerets – silk glands produce silk as liquid, emerges from spinnerets & solidifies on contact with air.
Spider silk is strongest natural substance known.
Malpighian tubules – excretory organs, extensions of gut.
Chelicerae house fangs to inject venom.

11. Spider Webs & Silk Stronger than steel
Many uses – webs, parachutes, guidelines, camouflage
Spider Webs & Silk

12. Arthropods: Class Diplopoda
Millipedes
2 prs. legs/body segment
Herbivorous

13. Arthropods: Class Chilopoda
Centipedes
1 pr. Legs/segment
Carnivorous
Venomous

14. Arthropods: Class Insecta
General Characteristics
3 body divisions - head, thorax, abdomen.
1 pr. antennae
3 prs. Legs on thorax, 1 pr./segment.
2 pr. wings (usually), 1 pr./1st two thoracic segments.

15. Insect Adaptations for Success
Flight
Easier to:
disperse to new areas.
find food.
find mates.
escape predators.

16. Insect Adaptations for Success
Small Size
Individuals need fewer resources.
Many individuals can inhabit small area without competition.
Easier to hide.

17. Insect Adaptations for Success
Exoskeleton
Great muscular leverage.
Waterproof.
Protective.
Flexible at joints.

18. Insect Adaptations for Success
Highly adaptable
short lifespan & generation time, many offspring.
Frequent mutations, some beneficial, so species can respond to environmental changes.

19. Insect Digestive System
Specialized Mouthparts
chewing – beetle, grasshopper
piercing/sucking –mosquito, true bugs
sponging - house fly
siphoning - butterfly

20. Insect Digestive/Excretory System
Crop - storage
Gizzard - grinds food
midgut (stomach) - digestion.
Gastric cecae - digestive glands.
Hindgut - nutrient absorption
Malpighian tubules - removes waste from blood, deposits in rectum.

21. Insect Circulatory System
Open
Dorsal aorta
Heart posterior, pumps blood forward.
Blood empties into coelom, bathes tissues as it flows to posterior.
Insect Circulatory System

22. Insect Respiratory System
Air intake through spiracles on sides of abdomen.
Air pulled into system of tubes (tracheae) that transport air directly to tissues.
Oxygen diffuses into tissues, CO2 out.

23. Nervous System & Sense Organs
Nerve ganglia - “brain”
Ventral Nerve cord.
Tympanum - sound sensing organ on abdomen or foreleg - not all insects have them.

24. Reproductive System Sperm deposited into female’s seminal receptacle.
Eggs fertilized internally.
Ovipositor used to create hole in substrate and/or deposit eggs.

25. Metamorphosis Incomplete 3 stages – egg, nymph, adult
Nymph – immature form, resembles adult, but w/ underdeveloped sexual organs.
Ex.- dragonflies, grasshoppers, true bugs, hoppers (Homoptera)

26. Metamorphosis Complete
4 stages – egg, larva, pupa, adult, each distinctly different.
Larva – specialized for feeding & growth.
Pupa – transformation stage – appears inactive, but big changes internally.
Adult – specialized for dispersal, mating, & feeding – different food than larva, no competition.
Butterflies, bees, beetles, flies.
Metamorphosis

27. Importance of Metamorphosis
One main factor in insect success.
Can exploit seasonally-available foods.
Different stages requiring lots of energy are separate - no competition between adults & larvae for food & space.
Insects can survive harsh weather as eggs or pupae.

28. Defense Aggression – stings or chemicals. Camouflage or hiding.
Advertise danger
Mullerian mimicry – all dangerous insects have similar coloration – predators only need to learn once.
Batesian mimicry – harmless insect evolves to resemble dangerous one. (monarch/viceroy)

29. Other Forms of Mimicry
Looking like part of the environment (stick, leaf, thorn, etc.) helps insects escape notice.

30. Communication Social insects have the most elaborate communication.
Communication may be by scent (pheromones), sound, touch, or light (fireflies).

31. Social Behavior Includes ants, termites, and colonial bees and wasps
Caste system – division of labor
Behavior is instinctive, not learned

32. Workers – responsible for all tasks of the colony except reproduction.
Drones – males, mate w/ queen (from another colony)
Queen – female, reproduction only.
Honeybee Castes

33. Workers Live about 6 wks. Tasks change w/ age.
1st task – “nurse” bees, feed larvae, drones, & queen.
Queen & youngest larvae get royal jelly.
2nd task – start producing wax to build & repair honeycomb. Also remove waste & dead bees, guard hive, & circulate air in hive.
Last task – gather nectar & pollen

34. Queen
Lives up to 5 yrs.
Queen develops from larva fed a continuous diet of royal jelly.
Adult queen secretes “queen factor”, pheromone preventing other female larvae from sexually maturing.
Mates once in her life on mating flight, stores sperm to fertilize eggs for rest of life.
Overcrowded hive, old queen takes half the workers & swarms to start new colony. Worker left behind produce more queens that fight for dominance.

35. Drones Males, develop from unfertilized eggs.
Large eyes – the better to see you with, my queen!
Contribute nothing to hive except reproduction.
Tolerated and fed by workers during seasons of plenty, but killed or driven from hive when food is scarce (winter).
Only a few hundred drones, compared to several thousand workers.

36. Waggle Dance & Round Dance
< of straight run to vertical equals < between food source to sun.
# waggles in straight run indicates distance.
Round dance indicates food nearby, but not direction.
Waggle Dance & Round Dance

37. Major Orders Orthoptera “straight-wing” Grasshoppers, crickets
Strong, muscular hind legs for jumping

38. Major Orders Odonata – “toothed wing” Dragonflies, Damselflies
Long, narrow, membranous wings

39. Major Orders Hemiptera – “Half-wing” True bugs
Half-membranous, half-leathery forewings
Large triangle on back

40. Major Orders Homoptera – “Like-wing, same-wing”
Cicadas, aphids, tree hoppers, frog hoppers
Hold wings at angle over back to form “roof”

41. Major Orders Coleoptera – “sheath wing” – beetles
Largest order, great diversity
Forewings hard or leathery, cover most or all of abdomen, meet in straight line on back

42. Major Orders Diptera – “two-wing” Flies, gnats, mosquitoes
One pair of wings

43. Major Orders Hymenoptera – “Membrane-wing” Bees, ants, wasps
Skinny “waist”

44. Major Orders Lepidoptera – “scale wing” Butterflies, moths
Wings covered in scales