Large Marsh Horse Fly
ExploreInsects
Large Marsh Horse Fly
tabanus autumnalis
The Large Marsh Horse Fly (Tabanus autumnalis) is a robust and highly active insect familiar to anyone spending summer days near European wetlands or pastures. Known for the painful bite delivered by the females, this species relies on the blood of large mammals—including livestock and occasionally humans—to properly develop its eggs. Meanwhile, the males live a much quieter life, acting as peaceful pollinators that feed exclusively on nectar and plant sap. Their ecological role is twofold: while adults are significant vectors of annoyance to grazing animals, both the adults and their predatory larvae serve as a crucial food source for birds, wasps, and amphibians. Despite their fearsome reputation, observing these flies reveals a fascinatingly complex life cycle and remarkable flight capabilities perfectly adapted to their marshy habitats.
Habitat: Commonly found in marshlands, wet meadows, damp woodlands, and nearby agricultural pastures where livestock graze.
Appearance
This moderately large fly measures roughly 16 to 22 millimeters in length and features a stout, dark grey to brownish-black body. Its most distinctive visual identifier is the pattern on its abdomen, which displays a central row of pale grey triangles flanked by lighter, roundish spots. The wings are predominantly clear, lacking the dark bands or mottling seen in some related species. In life, their large compound eyes often display striking, iridescent greenish or purplish hues. Males can be distinguished from females by their holoptic eyes, which meet in the middle of the head, whereas the female’s eyes are separated by a noticeable gap.
KingdomAnimaliaPhylumArthropodaClassInsectaOrderDipteraFamilyTabanidaeGenusTabanus
Category
InsectsRarity
Common
Danger
1/5 · Very low
Snaps
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Interesting facts
Only the female Large Marsh Horse Fly bites; males lack the necessary mouthparts for cutting skin and are harmless nectar-feeders.
The larvae are fierce predators that spend up to a year hunting worms and other small invertebrates in muddy soil before pupating.
Their bites are famously painful because they do not use a needle-like structure to pierce skin; instead, they use tiny serrated jaws to literally tear it open.
They are highly attracted to dark moving objects and can fly at speeds up to 30 km/h to catch up to a running horse or human.
Special abilities
Ability
Serrated Mandibles
Females possess highly specialized, scissor-like mouthparts designed to slice through thick mammalian skin to access pooling blood.
Ability
Anticoagulant Saliva
While feeding, females inject a specialized saliva that prevents the host's blood from clotting, ensuring a steady, uninterrupted meal.
Ability
Motion-Tracking Vision
Their massive compound eyes are highly sensitive to movement and dark silhouettes, allowing them to rapidly lock onto hosts from a distance.
Measurements & details
- Length
- 1-2 cm
- Wingspan
- 3-5 cm
- Weight
- 0.0002-0.0005 kg
- Lifespan
- 1-2 years
- Top Speed
- 30 km/h
- Clutch Size
- 100-1000
- Incubation
- 5-14 days
Diet & Feeding
Females require mammalian blood to produce viable eggs, while males strictly consume nectar and pollen; both sexes rely on plant sugars for daily energy.
Age differences: Larvae are entirely carnivorous, actively hunting small invertebrates, worms, and other insect larvae in muddy soil.
Primary Foods
- Mammalian blood
- Flower nectar
- Plant sap
- Pollen
Foraging Method
- Pursuit
Ecological connections
parasite
Domestic Cattle
Bos taurus
Females frequently feed on the blood of grazing cattle, causing irritation.
eaten by
Barn Swallow
Hirundo rustica
Hunted mid-air by fast-flying insectivorous birds like barn swallows.
eaten by
Sand Wasp
Bembix rostrata
Preyed upon by specialized predatory wasps that capture adult horse flies.
Traits
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Also known as
No aliases listed yet.
Collections
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Safety
Danger
1/5 · Very low
No special safety notes yet.
Frequently Asked Questions
How to identify Large Marsh Horse Fly?
The easiest way to identify Large Marsh Horse Fly is to use the Snappit nature identifier app.
How long is Large Marsh Horse Fly?
1-2 cm
What is Large Marsh Horse Fly's wingspan?
3-5 cm
How much does Large Marsh Horse Fly weigh?
0.0002-0.0005 kg
How long does Large Marsh Horse Fly live?
1-2 years
How fast can Large Marsh Horse Fly move?
30 km/h
What does Large Marsh Horse Fly eat?
Females require mammalian blood to produce viable eggs, while males strictly consume nectar and pollen; both sexes rely on plant sugars for daily energy.
Where is Large Marsh Horse Fly usually found?
Commonly found in marshlands, wet meadows, damp woodlands, and nearby agricultural pastures where livestock graze.
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