Forensic Entomology STEM

What is a Forensic Entomologist? A scientists who uses insects to help solve crime.

How do insects help solve crimes? A dead body attracts insects Insects lay eggs on the body. Hatching larva use body as food. Larva grow at a predictable rate. The Post-Mortem Interval (PMI-how long the body has been dead) can be determined by measuring and identifying the developing larva.

Forensic Entomology - The Crime Scene Video

Insect Succession Can be used to determine PMI Different species of insects prefer different stages of decomposition “I prefer my corpse dried” “The fresher the better!” “Juicy and smelly suits me just fine!”

Stages of Decomposition Living Initial decay Putrefaction Black putrefaction Butyric fermentation Dry decay http://australianmuseum.net.au/movie/Stages-of-decomposition/

Initial Decay--Day 1-3 Bacteria, present in the intestine to digest food, begin to eat away at the intestine itself. Intestine decays releasing bacteria and digestive enzymes into body cavity. Blow flies and house flies immediately begin to lay eggs on the defenseless body.

Putrefaction--Day 4-8 Bacteria continue to break down body producing large amounts of gasses Gasses inflate the body like a balloon. Larval flies move throughout the body, eating the partially digested flesh. Smell attracts other species flies and beetles. Rate of decay increases.

Black Putrefaction 10-20 days after death Bloated body collapses and flattens. Large amounts of fluids are released. Flesh is creamy and black where exposed. Several generations of flies are present. Wasps parasitize maggots.

Butyric Fermentation 20-50 days after death Remaining flesh is decomposed and corpse begins to dry out. Cheesy smell attracts new organisms. Body ferments and is covered with mold. Hardening of body makes it difficult for maggots to feed. Chewing beetles and their larva move in.

Dry Decay 50-365 days after death Body is dry and decays slowly. Hair and bones are all that remain. Hair is fed on my moths and bacteria. Mites may be present and feed on bacteria.

Insect Succession Body Condition Species Present Fresh Bloated Blow Fly Screw Worm Fly Flesh Fly House Fly Hairy Maggot Fly Bottle Fly Bloated Blow Fly Flesh Fly Hairy Maggot Fly House Fly Bottle Fly Roves Beetle Humpback Fly Cheese Fly Screw Worm Fly Scavenger Fly Active Decay Blow Fly Flesh Fly House Fly Rove’s Beetle Cheese Fly Carrion Beetles Advanced Decay Roves Beetle Cheese Fly Checkered Beetles Dried Remains Picnic Beetle Dermestid Beetle

Factors that affect decay rate and growth rate of flies Temperature--the warmer the climate, the faster the decay. Season--early spring will decay slower, because the insect population is still relatively low. Degree of corpse enclosure--the more exposed, the faster the decay.

Classification of a House Fly Kingdom - Animal Phylum - Arthropods Class - Insects Order - Diptera (All Flies) Family - Muscidae Genus - Musca Species - domestica Musca domestica

Life Cycle of a Fly Flies lay 100-150 eggs at a time. Eggs hatch-1st instar Larva molt-2nd instar Larva molt again-3rd instar Pupa -- cocoon Adult fly

Another Look

Egg Stage Most flies lay 100-150 eggs at a time. The eggs are small and oblong. They are white or cream colored. It takes 8-14 hours for the eggs to hatch after they have been laid. Flies only lay eggs in daylight.

Another look at eggs

Larva Molt (shed their skin) twice after hatching Breath through anterior and posterior slits called spiracles

Instar Maturation of Larva 1st instar larva take 8-14 more hours until they are ready to molt. 2nd instar larva take 2-3 days to molt. 3rd instar larva take 7-8 days until pupal maturation. Pre-pupal 3rd instar larva.

Spiracles are distinct Different species of fly larva have different spiracle characteristics Peritreme Spiracular Slits

Identifying Maggots by Spiracular Slits Maggots can be identified by their distinguishing spiracular slits.

Pupa Once larva mature they stop eating and metamorphose into an adult fly.

Basic Anatomy of an Adult Fly Insects have three body parts Head Thorax Abdomen Six Legs Wings