3.2 Flies, Gnats, and Occasional Invaders

Flies, Gnats, and Occasional Invaders

Flies, gnats, and occasional invaders are primary targets for Branch 2 General Pest control. They enter structures looking for shelter, moisture, or breeding media. Identifying these pests correctly is vital, as control strategies differ fundamentally between filth flies breeding in sewage and arachnids wandering indoors from vegetation.

Filth and Nuisance Flies

Flies undergo complete metamorphosis (egg, larva, pupa, adult). Managing flies relies heavily on source reduction (sanitation) rather than chemical application.

1. House Fly (Musca domestica)

• Biology and Mouthparts: House flies possess sponging mouthparts. They cannot bite; instead, they regurgitate digestive enzymes onto solid food to liquefy it before sponging it up.
• Public Health Danger: Because they feed on trash, feces, and decomposing organic matter, and then land on human food, they serve as mechanical vectors for pathogens such as Salmonella and E. coli.
• Control: The primary control method is sanitation (sealing trash receptacles, clearing pet waste, cleaning dumpsters). Chemical controls like bait stations or pyrethrin space sprays are secondary.

2. Fruit Fly (Drosophila spp.)

• Identification: Small flies (3-4 mm) with characteristic bright red eyes (though some species have dark eyes).
• Breeding Habitats: They breed in fermenting or decaying organic matter. Common locations include overripe fruits, rotting vegetables, garbage disposals, recycling bins containing beer/soda cans, and dirty drains.
• Control: Locate and eliminate the fermenting organic source. Simply spraying adults is ineffective if the breeding medium remains.

3. Phorid Fly (Megaselia scalaris)

• Identification: Small, humpbacked flies with an enlarged thorax and a downward-pointing head. They have a distinct habit of running rapidly across surfaces rather than taking flight immediately.
• Breeding Habitats: Phorid flies breed in wet, decaying organic matter. They are notorious in commercial kitchens for breeding in grease traps, sewers, and dirty drains.
• Sub-Slab Infestation (Exam Focus): A major challenge in California structures occurs when under-slab sewer lines break. Phorid flies breed in the sewage-contaminated soil beneath the concrete slab and enter the building through expansion joints or cracks. Resolving this requires excavation or pipe repair, not surface pesticide applications.

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Occasional Invaders

Occasional invaders are pests that live outdoors but enter structures due to environmental changes (excessive heat, heavy rain, or drought).

1. Earwigs (European Earwig: Forficula auricularia)

• Identification: Flat, dark reddish-brown insects with a pair of prominent, forceps-like pincers (cerci) at the tip of the abdomen. The cerci are used for defense, prey capture, and mating. Male cerci are strongly curved, while female cerci are relatively straight.
• Habits: Earwigs are nocturnal, preferring moist, dark harborages under mulch, stones, woodpiles, and landscape timber. They undergo gradual metamorphosis.
• Exclusion: Keep mulch away from foundations and seal cracks at ground level.

2. Centipedes (Class Chilopoda)

• Identification: Elongated, flattened bodies with exactly one pair of legs per body segment. The first body segment features appendages modified into sharp, venomous claws (forcipules) used to paralyze insect prey.
• Behavior: Fast-moving, nocturnal predators. They are beneficial because they eat other pests, but their appearance and venomous bite make them structural pests.
• Centipede vs. Millipede (Exam Comparison):
  • Centipedes (Chilopoda): One pair of legs per segment, fast-moving, carnivorous, venomous claws.
  • Millipedes (Diplopoda): Two pairs of legs per segment, slow-moving, herbivorous/detritivores, non-venomous (though some secrete foul-smelling fluids).

3. Spiders (Class Arachnida)

Spiders are arachnids (eight legs, two body regions: cephalothorax and abdomen) and are beneficial predators. Only a few species pose medical concerns.

Western Black Widow (Latrodectus hesperus)

• Identification: The adult female is shiny black, with a large globular abdomen and a distinctive red or orange hourglass mark on the underside.
• Venom: Neurotoxic venom, which causes severe muscle pain, cramping, and systemic symptoms.
• Webs and Harborages: They spin messy, tangled, irregular webs in dark, undisturbed areas, such as crawl spaces, garages, woodpiles, water meter boxes, and under outdoor furniture.

The Brown Recluse (Loxosceles reclusa) — The California Exam Trap!

• Identification: Light brown with a violin-shaped mark on the cephalothorax. Necrotoxic venom.
• SPCB EXAM TRAP: The Brown Recluse is not established in California. While desert recluse species exist in dry desert regions of southeastern California, they are rarely found in structural environments. If a customer reports a 'brown recluse' in a coastal or urban California home, it is almost certainly a misidentification of a harmless cellar spider or grass spider. Claiming a brown recluse infestation on a service report is a major professional error.

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SPCB Exam Traps

1. The Recluse Trap: The SPCB exam will try to trick you with questions about the Brown Recluse in California. Remember: Loxosceles reclusa is NOT native or established in California.
2. Fly Breeding Media: Match the fly to its breeding site. Fruit flies breed in fermenting fruit and sweet substances; phorid flies breed in decaying organic matter and sewer lines; house flies breed in manure and trash.
3. Centipede Segment Legs: Remember the rule: Centipedes have one pair of legs per segment, while millipedes have two pairs of legs per segment.

Real-World Scenario

A commercial restaurant experiences a persistent small fly problem. The technician finds red-eyed fruit flies breeding in a bin of rotten onions. They also find humpbacked phorid flies running on the floor near a floor drain. The technician should recommend clearing the onions to solve the fruit fly issue, and scrubbing the organic buildup inside the drain line with an enzymatic cleaner to resolve the phorid fly infestation.