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.

1 st Instar 0-36 hours after eggs are laid 2 mm to 5 mm 0 to 1 spiracle slits

2 nd instar hours 5 mm to 10 mm 2 spiracle slits

3 rd 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!