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ACE Prep · Module 7 of 11

Flies

Quick answerUpdated September 24, 2026

What does ACE module 7 cover?

Flies are divided into filth breeders (breed in decaying matter), small flies (fruit flies, phorid flies, fungus gnats), indoor invaders (cluster flies), and outdoor breeders (house flies, mosquitoes). All have complete metamorphosis.

Key factApproximate exam weight: ~8%.

Reviewed by LTK editorial team

Must-know facts

  • All flies (Order Diptera) have complete metamorphosis: egg → larva (maggot) → pupa → adult. Two functional wings (halteres replace rear wings).
  • House fly (Musca domestica): 4–7 mm, gray with 4 stripes. Breeds in manure and garbage. Minimum 7–10 day development. Harbors 100+ pathogens. Sponging mouthparts — cannot pierce skin.
  • Stable fly: looks like house fly but has piercing-sucking mouthparts and bites. Associated with wet organic matter high in nitrogen.
  • Blow flies and flesh flies: carrion feeders. Presence indicates a dead animal somewhere in or near the structure. Late-instar (3rd instar) larvae have a wandering phase — most likely to be seen by client.
  • Fruit flies (Drosophila): attracted to fermenting organic matter (drains, fruit, spilled alcohol). Control = eliminate breeding source.
  • Phorid flies (humpbacked flies): associated with decaying organic matter in drains, sewers, under slabs. Characteristic humpbacked profile and rapid stop-start movement.
  • Fungus gnats: breed in moist potting soil/organic matter. Most common small fly complaint in offices with potted plants.
  • Drain flies/moth flies: breed in organic film inside drains. Adults look like tiny moths.
  • Cluster fly (Pollenia rudis): outdoor fly, parasite of earthworms. Overwinters in attics/walls. Slightly larger than house fly, golden thorax hairs.
  • Mosquitoes: aquatic breeders (Aedes, Culex, Anopheles). Disease vectors: West Nile virus (Culex), Lyme-adjacent (Aedes), encephalitis, dog heartworm. Control = breeding site elimination, ULV fogging, resting site residual.

What the exam likes to ask

  • Late-instar fly larvae have a wandering behavior — the life stage most likely seen by clients in a carrion infestation.
  • If asked about gnats in an office with plants: fungus gnats, not fruit flies.
  • Cluster flies are identified by golden hairs on thorax and are outdoor parasites of earthworms — they do NOT breed indoors.
  • House fly vs. stable fly: if it looks like a house fly but bites, it's a stable fly.

Field takeaways

  • Small fly complaints almost always point to a breeding source — find and eliminate it before spraying.
  • Sanitation and source reduction are the most effective fly control tactics — chemicals are supplementary.
  • Documentation of fly monitoring (light trap catch counts, date/location) helps demonstrate control effectiveness to commercial accounts.

Listen, watch, read

Podcast

Household Flies Are Biological Cheat Codes

Fly biology, development cycles, breeding site identification, and urban fly management strategies.

Slide deck · 15 slides

Urban Fly Diagnostics

View the slides

Module 7 quiz

25 questions. Answer them all, then grade to see the reasoning.

  1. Q1Large numbers of blow flies appear inside a home in the middle of winter. What should the inspection look for first?
  2. Q2Small fuzzy flies with moth-like wings held roof-like over the body are resting on a bathroom wall, and larvae are found in the film inside a drain. Which fly is it?
  3. Q3A client describes a fly that looks identical to a house fly but bites. The most likely species is
  4. Q4Cluster flies (Pollenia rudis) differ from house flies in that they
  5. Q5The most effective long-term control for small flies (fruit flies, drain flies, phorid flies) is
  6. Q6A tiny fuzzy fly with broad, hairy wings folded like a tent over its back rests on a shower wall. It is most likely a
  7. Q7A small hump-backed fly tends to run quickly across surfaces before it flies. It is most likely a
  8. Q8Phorid flies keep coming back in a restaurant even after every drain has been cleaned. What is the most likely hidden source?
  9. Q9In flies, the hind wings are reduced to small knobbed balancing organs called
  10. Q10What is the best way to control fungus gnats breeding in office potted plants?
  11. Q11Larger, dark-eyed Drosophila are found around floor drains, garbage containers and dish machines rather than fruit. They are most likely
  12. Q12In midwinter, large metallic blue-green flies suddenly appear at the windows of a house, along with a bad odor from one wall. The most likely cause is
  13. Q13A gray fly with three dark stripes on the thorax and a checkerboard-patterned abdomen is most likely a
  14. Q14House flies are numerous near a restaurant's back door. Where should the inspection start?
  15. Q15In hot summer weather, a house fly can go from egg to adult in about
  16. Q16What gives the best long-term mosquito control around a home?
  17. Q17A black-and-white mosquito bites during the day and breeds in small backyard containers. It is most likely
  18. Q18Which mosquito genus is the main vector of West Nile virus in the United States?
  19. Q19Bti (Bacillus thuringiensis israelensis) placed in standing water controls mosquitoes by
  20. Q20A client is alarmed by 'giant mosquitoes' with very long, fragile legs resting on the house in spring. They do not bite. They are most likely
  21. Q21Tough, flattened, leathery fly larvae are crawling across a floor some distance from a compost or manure pile. They are most likely
  22. Q22A large fly with big, often colorful eyes bites painfully around a farm pond in summer, and only the females bite. It most likely belongs to the family
  23. Q23When should exclusion work be done to keep cluster flies out of a home?
  24. Q24Stable flies most often breed in
  25. Q25Small flies are emerging in a dry storeroom where no fruit is kept. What is the most productive way to inspect?

0 of 25 answered

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