Insect Biology

Entomology 2

Phylum Arthropoda

• Largest phylum on Earth– 75% of all living species

• Class Arachnida (spiders, ticks, scorpions…)

• Class Crustacea (shrimp, crabs, crayfish…)

• Class Insecta

• Class Diplopoda (millipedes)

• Class Chilopoda (centipedes)

Class Insecta

• Largest class of animals on Earth– ~800,000 species

• Over 200 million per person• History includes over 250,000,000 years of Earth

history• Many species still undiscovered• Populate EVERY habitat on Earth• Approximately 90,000 to 125,000 species in

North America alone

Class Insecta

• 3 body parts– Head– Thorax– Abdomen

• 6 jointed legs– 3 pairs on thorax

• Exoskeleton• 2 antennae• Compound eyes

Class Insecta

• Metamorphosis– Describes the way by which insects change, grow,

develop from egg to adult– All insects undergo some type of metamorphosis due to

exoskeleton– Referred to as “moults”– Many adults do not feed…adult phase for mating only

• Incomplete (12%) – Gradual change over time– Young looks similar to adult

• Complete (88%)– 4 distinct stages

Incomplete Metamorphosis

• Egg

• Nymph– Small adult– Lacks wings– Several stages

• Adult

Complete Metamorphosis

• Egg• Larva

– Worm like– Maggot, Caterpillar…– Molt several times

• Pupa– Cocoon

• Adult

Order Diptera

• “Two wings”

• Includes flies of all varieties, mosquitoes, gnats

• Many feed on rotting flesh or other decaying matter– Highly in tuned sense of smell is common

Order Diptera

• Forewings are membranous– Used for flying

• Hindwings are for balancing– “Halteres” – knob like

• Metamorphosis-Complete

• Mouthparts-sucking (most)– All forensically valuable species

Blow/Bottle Flies

Flies usually infest first because larvae (maggots) can survive in the liquid medium of the corpse.

Blow Flies

• Kingdom – Animalia

• Phylum – Arthropoda

• Class – Insecta

• Order – Diptera

• Family – Calliphoridae

• Genus– Cynomyopsis

• Species– cadaverina

Medicinal Uses of Maggots

• Well documented cases in medicine for centuries

• Maggots will selectively eat dead tissue before living tissue

• “Maggot therapy” is an accepted method for fighting infections– Now seeing a resurgence

due to MRSA*, etc.

WARNING – GRAPHIC IMAGES

*Methicillin-resistant Staphylococcus aureus

Maggots in leg amputation

Maggots in Wound

Maggots in small cavity wound

Order Coleoptera

• “Sheathed wing”• Largest group of insects

– 25% of ALL living species

• Includes the beetles and weevils• 350,000 known species• Forewings are hard; cover hindwings• Hindwings are membranous

– Used for flight– Wings meet in straight line down the middle of the back

• Metamorphosis-Complete• Mouth parts-Chewing• Usually eat the fly larvae rather than the corpse

Carrion Beetles• Kingdom

– Animal• Phylum

– Arthropoda• Class

– Insecta• Order

– Coleoptera• Family

– Silphidae• Genus

– Necrophila • Species

– americana

Determining Time of Death

• Known as Post-Mortem Interval (PMI)

• Use insect stage (instar) to determine the time since death– Maggots have 3 instars (or molts) before pupa

• Must consider:– Temperature– Time of day– Exposure of corpse (air, soil, water)

PMI Determination

• ID species– Different species usually arrive in specific

orders based upon senses

• Document larval length • Measure maggot size

• Determine instar– Can be determined by examining body

features

• Calculate PMI

Species Identification

• Look at structural differences– Body Shape– Color– Texture– Mouth hooks (at tapered end)– Spiracles (at blunt end)

Determine Instar

• Look at the Posterior End of maggot

• Breathing “spiracles” are located here

• Count the number of spiracle slits to determine the instar

Spiracle Slits

Spiracles used for breathing by the blow fly larvae.

Mouth Parts

Mouth hooks used by blow fly larvae to attach themselves to a food source. As a reminder, the larvae have no legs.

1st Instar

• 0-36 hours after eggs are laid

• 2 mm to 5 mm• 0 to 1 spiracle

slits

2nd instar

• 36-72 hours• 5 mm to 10 mm• 2 spiracle slits

3rd Instar

• 72 hour +• 15 mm to 20 mm

• 3 spiracle slits

Pupa

• Pupa cases usually found within a few feet of food source

• Cases can last for decades

Establishing Time of Death

Stages of Decomposition Experiment

WARNING – GRAPHIC IMAGES

Living Pig

0 to 3 days

Fly Eggs in EAR

4 to 10 days

10 to 20 days

20 to 50 days

50 to 365 days

Facts!

• In warm weather, maggots can digest 60% of a human body in less than a week!