Fauna
Insect

Three-spotted Horse Fly

Tabanus trimaculatus

Also known as Three-spotted Horsefly, Trimaculate Horse Fly

Three-spotted horse flies are robust insects easily identified by the trio of prominent white triangles running down the midline of their dark abdomen. Females use specialized blade-like mouthparts to slice skin for the blood meal necessary to develop eggs, while males feed strictly on nectar and plant juices. Their carnivorous larvae inhabit saturated mud along stream margins and swamp edges where they actively hunt soft-bodied invertebrates.

DiurnalBiting InsectWetland Insect
Three-spotted Horse Fly reference1 / 7
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Not EvaluatedConservation statusIUCN Red List categoriesLCNTVUENCREWEXNot Evaluated — not placed on the risk ladderRed List categories, explained →
Key facts
Diet & preyMammal blood, Floral nectar, Insect larvae
Predators
  • Dragonflies
  • Songbirds
  • Orb-weaver spiders
ThreatsWetland drainage, aquatic pollution, and broad-spectrum pesticide application
HabitatsWetlands, stream margins, wet pastures, and moist deciduous woodlands
Life span1 to 2 years (mostly as larvae; adult phase lasts 3 to 4 weeks)
Classification
  1. OrderDiptera
  2. FamilyTabanidae
  3. GenusTabanus
  4. SpeciesTabanus trimaculatus
Range & activity
Range data is not available yet.
Safe observation
Interaction riskLow
  1. Low
  2. Moderate
  3. High
  4. Very high
Why interaction risk is low
Females deliver a painful bite; wear long sleeves and pants in humid or marshy woods.
Why it is dangerous
Females possess blade-like mouthparts that slice skin to ingest blood, causing sharp localized pain and itchy swelling.
How to recognize a risky encounter
Look for three distinct white or pale triangular spots along the center of a dark brown to black abdomen.
What to do
Avoid approaching swarming individuals near livestock or water, and move away steadily if targeted.
Responsible observation
  • Dress defensively: Wear light-colored, loosely fitted long sleeves and pants near wetland habitats.
  • Observe resting males: Males gather on sunny leaves near water and pose no bite risk.
  • Use insect repellent: Apply EPA-registered repellents containing DEET or Picaridin to deter biting females.
Related species
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Mystic Meadows

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