Insects or not, that is the question

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Insects or not, that is the question
Insects compose a single class of a highly
diverse collection of animals. All these animals
form a great Phylum, the Arthropoda.
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Phylum Arthropoda
Arthro joint (G) Poda appendage (G)
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All arthropods have these characteristics
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Exoskeleton?
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• So that you-all remember the arthropods, lets
  divide them into two subphyla, the Chelicerata
  the Mandibulata.
• Each subphyla is divided into classes.
• Youll see the logic in this.

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Mites Ticks
Spiders
Millipedes
Centipedes
Arachnids
The Arthropoda
Scorpions Pseudo- scorpions
Insect (Insecta)
Sea Spiders
Horse shoe crabs
Crustaceans
Mandibulata
Chelicerata
Onychophora
Proto-arthropod
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• The best way to sort out the arthropod classes
  is to look at their probable evolution.
• in particular the evolution of their appendages.

• Kept track of
• appendages
• through
• movements
• of appendages
• in embryogenesis
• and (2) attachment.

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Look at the appendages after blastogenisis!
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In the Chelicerata the embryonic appendages never
enter the mouth. In the Mandibulata the
embryonic appendages enter the mouth and form the
labrum, mandibles, maxillae, labium.
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Yes, Virginia, there are onychopherans
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Fossil and real onychophorans
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The Trilobata
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Class Arachnida
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Chilerate Mouthparts
Fused Chelicerae
c Chelicerae p Pedipalps l Legs
Pedipalps
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The Class Arachnida
Acarina the mites
Acarina the ticks
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Many mite species are horrendous problems to
agriculture and horticulture
Spider mites on shade trees
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Acarologist
Scab mites on mammals
(Sarcoptes scabiei, responsible for mange or
scabies)
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Ticks are vectors of many diseases of animals and
humans.
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Expanding sore resulting from bite of tick-vector
of Lyme Disease
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• Spiders
• Three kinds, hunting (jumping),
• crab spiders and orb weavers
• All spiders are predators and,
• as such, beneficial.

Hunting spider carrying off larva of the
western spruce budworm.
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The Spiders
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• The Insecta
• Three body regions
• - head
• - thorax
• - abdomen
• One pair antennae
• Adults mostly winged
• Three pairs of legs.

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Where to begin? What one feature would represent
the key to success for the Insecta? How about
their exoskeleton, in particular the cuticle?
Why?
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Oriented wax molecules on epicuticle
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Live insect expends energy to keep wax molecules
aligned.
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• The cuticular exoskeleton, when tanned, offers
  great mechanical protection, as well as
• Prevents entry of other organisms
• Again, excellent framework for muscle
  attachments and, of course, awesome mechanical
  advantages

From Snodgrass text
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(continued advantages of exoskeleton)

• Provides for insect external tactile sensory
  structures, setae
• Setae are sense receptors, poison hairs,
  scales, spines etc.

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How else other than direct use of O2 can you get
7,000 wing beats/sec or fly 80mph.
The human botfly
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Since all arthropods, including the insects,
have a hard exoskeleton they have to change it in
order to grow. This process is called MOLTING.
Cicada molting
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Molting of the exoskeleton
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The old
The new
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Insect exoskeletons are mostly a single surface
a Moebius Ring
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The silver fish order, Thysanura, has no
metamorphosis.
Jumping bristletail (found in the forest)
Common silverfish
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Mayflies (order Ephemeroptera) have incomplete
metamorphosis
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The greatest invention of all, of course, is
Complete Metamorphosis and the PUPA!
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Ive just got to move on even if
general entomology is so interesting.
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Insect Mouthparts
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The insectan mouthparts
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Look at the variations found in the chewing mouth
parts
Fierce predators Tiger beetles
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Mouth parts Piercing-sucking (order Hemiptera
the bugs)
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Piercing-sucking mouth parts of the Hemiptera
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More, piercing-sucking mode of feeding.
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Insect Legs
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Insect legs
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Insect digestion?
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Digestion in insects
Guts of a larva
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