7A Ch11 Cheat Sheet: Houseflies & Their Relatives

🎯 Top 5 Traps

1

Diptera have ONE pair of wings — not two. This is the defining feature of the entire fly order. Most flies are small and soft-bodied with two large eyes on the front of the head. The order divides into two groups by form: Group 1 (gnat/mosquito-like, long antennae, slender legs; larvae have head capsules and live in water/moist soil); Group 2 (stout bodies, short or invisible antennae; larvae lack discernible heads, often maggot-like).

2

Fruit flies and phorid flies look alike but are biologically very different — and are mistaken for each other. FRUIT FLY: bright red eyes, yellowish-brown body, attracted to fermenting fruit/yeast, wing veins EXTEND to wing tip. PHORID FLY: dark brown, HUMPBACKED appearance (small head low on front bulge of thorax), RUNS IN SHORT JERKS, infests decomposing matter and buried sources, wing veins do NOT extend to wing tip. Same size (~1/8 inch); completely different management.

3

Phorid flies can EMERGE FROM SEVERAL FEET BELOW GROUND — through cracks in concrete floors or around floor drains. Buried animals, broken sewer lines, and bodies in mausoleums support immense numbers. When sewer lines under buildings are repaired, the SEWAGE-CONTAMINATED SOIL must also be removed — fixing the pipe alone is not enough.

4

Cluster fly larvae PARASITIZE EARTHWORMS — they don't feed on garbage or carrion like other blowflies. Despite being in the blowfly family (Calliphoridae). Cluster flies also overwinter as adults in attics ("attic fly"), then emerge to windows on warm winter days. Frequently finding dead flies at windows is a key indicator of an attic fly infestation.

5

Garbage must be removed from premises TWICE A WEEK — and OPEN DOORS are the most common fly entry route. Look for door props, hooks, broom handles holding doors open, and doors that don't fit tightly. Replace WHITE security lights with YELLOW so flies are not attracted to the building. Install air curtains where doors must remain open for deliveries.

🔢 Numbers You Must Know

Number

What It Represents

1 pair of wings

Defining feature of the order Diptera (2 wings total, vs. 4 wings in most insects)

1/4 inch

Length of LARGE flies: housefly, face fly, blowfly (cluster fly slightly more than 1/4 inch; flesh fly more than 1/4 inch)

1/8 inch

Length of SMALL flies: fruit fly, phorid fly, moth/drain fly

6 to 10 days

Housefly larval maturation in favorable weather

3 to 9 days

Blowfly larval maturation in favorable weather

About 1 week

Fruit fly (Drosophila) entire life cycle in fermenting fruit

Twice a week

Required garbage removal frequency from premises (per chapter recommendation)

3 distinct stripes

On flesh fly (Sarcophagidae) thorax — key ID feature; abdomen is gray checkerboard

Several feet of soil

Distance phorid flies can emerge upward through to reach buildings from underground sources

2 large eyes

On the front of the head — typical of all flies

2 groups

Order Diptera divides into Group 1 (small/gnat-like, long antennae, head-capsule larvae) and Group 2 (stout bodies, short antennae, headless maggot-like larvae)

🔀 Easily Confused

Pair / Group

Distinguishing Feature

Group 1 vs Group 2 Diptera

Group 1: small, gnat- or mosquito-like adults; long antennae; slender legs. Larvae HAVE head capsules; live in water or moist soil. Group 2: stout-bodied adults; short or not-visible antennae; usually not long-legged. Larvae LACK discernible heads; maggot-like; live in water, filth, soil, carcasses, plant or animal tissues.

Housefly vs Face fly

Both Musca; both 1/4 inch; both have dull gray thorax with dark stripes and dull abdomen with yellow sides — practically indistinguishable visually. Housefly (M. domestica): garbage and any manure (horse, cattle, poultry, pet) and filth. Face fly (M. autumnalis): needs FRESH CATTLE MANURE for egg laying.

Housefly vs Flesh fly

Housefly: 1/4 inch; dull gray thorax with dark stripes (number not specified); dull abdomen with yellow sides. Flesh fly: MORE than 1/4 inch; dull gray thorax with THREE distinct dark stripes; GRAY CHECKERBOARD abdomen. Flesh fly = larger + 3 stripes + checkerboard abdomen.

Blowfly vs Cluster fly

Both family Calliphoridae. Blowfly: 1/4 inch; SHINY thorax + abdomen — metallic green, bronze, blue, or black. Lives on dead animals, meat scraps, wet garbage. Cluster fly: slightly more than 1/4 inch; thorax covered with GRAY OR YELLOWISH HAIRS (NO stripes); dark gray abdomen with light patches. Larvae PARASITIZE EARTHWORMS. Overwinters as adult in attics.

Fruit fly vs Phorid fly

The chapter's central small-fly distinction. Fruit fly (Drosophila): bright red eyes; yellowish-brown body with yellow-banded abdomen; wing has thickened front-margin vein extending to WING TIP plus 4 other long veins; attracted to fermenting yeast (fruit, beer, sour mops). Phorid fly: dark brown; HUMPBACKED (small head low on front bulge of thorax); wing veins SHORT and thickened on fore margin, NOT extending to wing tip; runs in SHORT JERKS; infests buried decomposing matter and broken sewer lines.

Phorid fly vs Drain fly

Both are small flies that emerge from below. Phorid: comes from underground sewer lines, buried garbage, dead animals; can travel several feet through soil to reach surface. Drain fly: comes from gelatinous material in sink drain traps and sewers; enters dwellings when drain traps DRY OUT. Different remediation: phorids need soil removal; drain flies need drain trap cleaning.

Fungus gnat vs Midge

Both mosquito-like Group 1 flies. Fungus gnat: slender, delicate; larvae in moist soil feeding on fungi; indoors infest FLOWERPOTS; build up in pigeon droppings on outside ledges. Midge: looks very much like mosquito but DOES NOT BITE; larvae live in WATER (especially quiet, still water); flies to lights — manipulate lighting to control.

Drain trap dried out vs Drain trap with larvae

Dried out: large numbers of drain flies enter dwellings from the sewer through the unsealed trap. With larvae: drain flies breed in the gelatinous material — adults will constantly emerge unless drains are cleaned mechanically or with drain cleaners. Both problems can co-occur.

🪰 Large Fly Species ID Quick Reference

Species

Size / Color

Habitat / Key Feature

Housefly
Musca domestica

1/4 inch; dull gray thorax with dark stripes; dark dull abdomen with yellow sides

Garbage and ALL manure types (horse, cattle, poultry, pet) and filth accumulations. Most common indoor fly. Most commonly enters through OPEN DOORS.

Face fly
Musca autumnalis

1/4 inch; resembles housefly — dull gray thorax with stripes, dull abdomen with yellow sides

Needs FRESH CATTLE MANURE for egg laying. Visually indistinguishable from housefly without lab examination.

Flesh flies
Family Sarcophagidae

MORE than 1/4 inch; dull gray thorax with THREE distinct dark stripes; GRAY CHECKERBOARD abdomen

Meat scraps, dead animals, dog excrement, pet manure. Larger than housefly; the 3-stripe pattern + checkerboard abdomen are diagnostic.

Blowflies
Family Calliphoridae

1/4 inch; SHINY metallic — black, green, bronze, or blue (some have metallic blue abdomen with dull thorax)

Dead animals, meat scraps in garbage, wet-mixed garbage, dead birds and rodents in WALL VOIDS and CHIMNEYS. Larvae mature in 3-9 days.

Cluster fly
Pollenia rudis (Calliphoridae)

Slightly more than 1/4 inch; thorax covered with GRAY OR YELLOWISH HAIRS (no stripes); dark gray abdomen with light patches

Larvae PARASITIZE EARTHWORMS — unique among large flies. Classic "ATTIC FLY" — overwinters as adult in attics; emerges on warm winter days; flies dead at windows = attic fly indicator.

🦟 Small Fly Species ID Quick Reference

Species

Size / Key ID

Source / Control Note

Fruit fly
Drosophila

1/8 inch; bright RED EYES (some dull dark red); yellowish-brown head/thorax; light brown to dark abdomen with yellow bands. Wing has thickened front-margin vein extending to WING TIP + 4 other long veins.

Attracted to FERMENTING materials: ripe fruit, beer, fermenting water in refrigerators/humidifiers, sink drains, sour mops, fermenting pet food. Use BANANA-BAITED traps to find heavy infestation areas. Common in orchards, breweries, restaurants, canneries, hospitals, homes.

Phorid fly
Family Phoridae ("humpbacked")

~1/8 inch or slightly smaller; dark brown; HUMPBACKED (small head low on front bulge of thorax); wing veins SHORT and thickened on fore margin only — do NOT extend to wing tip; other veins weak/invisible. RUNS IN SHORT JERKS.

Decomposing plant or animal matter — buried animals, garbage, BROKEN SEWER LINES, bodies in mausoleums. Adults emerge upward through several feet of soil. Remove sewage-contaminated soil when sewer lines are repaired.

Moth/Drain fly
Family Psychodidae

1/8 inch; dark color from tiny hairs covering wings; wings held in ROOF-LIKE fashion over body; LONG DROOPING ANTENNAE

Larvae live in GELATINOUS MATERIAL in sink drain traps and sewers. Enter dwellings when drain traps DRY OUT. Clean drain traps mechanically or with drain cleaners. In sewage treatment plants, control via reverse/back-flushing of filter beds.

Fungus gnat
Mycetophilidae + Sciaridae

Slender, delicate, mosquito-like

Larvae infest MOIST SOIL and feed on fungi from decaying vegetation. Indoors: FLOWERPOTS. Build up in PIGEON DROPPINGS on outside ledges; enter through nearby windows.

Midge
Family Chironomidae

Looks very much like mosquito BUT DOES NOT BITE

Larvae in WATER (especially quiet, still water). Adults are food for spiders on buildings/monuments. Fly to lights, enter through gaps. Pesticides generally NOT useful — manipulate lights to shine away from buildings. Some midge larvae indicate larger pollution problems.

💡 Memory Hooks

Diptera etymology: "Di-ptera = TWO wings (one pair)." Other insects have 4 wings; flies have 2. The name itself encodes the defining feature.

Fruit vs phorid: "Fruit fly likes the fruit; phorid fly likes the floor." Fruit flies in fermenting food; phorids emerging from sewers, buried garbage, and broken pipes through floor drains.

Cluster fly oddity: "Cluster larvae attack worms — only large fly without garbage taste." Earthworm parasitism is unique. Adults love attics on warm winter days.

Garbage cadence: "Twice a week, garbage out." The standard schedule for fly prevention.

Light color: "Yellow lights for fewer flies." Replacing white security lights with yellow reduces fly attraction to buildings.

Drain fly cue: "Drain dries, drain flies arrive." When trap water evaporates, drain flies enter from the sewer below.

Midge vs mosquito: "Midges look mean but don't bite." Identical body plan; no proboscis-style biting. Larvae in still water.