Currently viewing the category: "Horse Flies and Deer Flies"
What's That Bug? does not endorse extermination

Subject: Female Dark Giant Horsefly?
Location: South West Wales
July 4, 2017 12:24 pm
Hi, found this insect on my window this morning, I’ve asked several friends to help identify it but the most likely contender seems to be the Dark Giant Horsefly and for it to be a female due to the band between the eyes. Would you agree?
Signature: Justin

Female Dark Giant Horsefly

Dear Justin,
We agree that this is a female Dark Giant Horsefly, though we do have one comment regarding the common name.  In North America, we reserve compound names using fly to refer to creatures that are not Flies, like Butterflies, Fireflies, Dobsonflies and Dragonflies, and the modifying naming strategy like Crane Flies, Fruit Flies and Flesh Flies, as well as Horse Flies, is used to identify true Flies in the order Diptera.

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Subject: I was wondering what this was
Location: Central Scotland
July 1, 2017 6:09 am
We were trying to find out what this was. We had thought it was somekind of hoverfly but we have never seen one so big.
Signature: Best wishes, Dawn

Dark Giant Horse Fly

Dear Dawn,
This is a female Horse Fly,
Tabanus sudeticus, and we just posted images of a male.  Only female Horse Flies are blood-sucking biters, and they can be distinguished quickly from males by the spacing between their eyes.  Males do not have a space between their eyes.  According to Influential Points, the common name for this species is Dark Giant Horse Fly and the site states:  “The dark giant horsefly flies in July and August and commonly feeds on the blood of cattle and ponies. In Europe … Tabanus sudeticus flies from the end of June and through July and August. Krčmar (2005)  reports that it reaches its maximum abundance in third week of July. In Britain it mainly lives in boggy areas in the north and west, although it is also quite common in the New Forest. Tabanus sudeticus is distributed widely in northern Europe into Russia.”  According to iNaturalist:  “a species of biting horse-fly. It is the heaviest fly in Europe.”  According to the Nature Net Ranger’s Blog:  “This is Tabanus sudeticus, sometimes called the dark giant horsefly. It seems, oddly enough, that this impressive insect has not really got a commonly-accepted English name. It’s referred to in one place as the “dark behemothic horsefly”: a charmingly descriptive name, albeit a little cumbersome. Yes, it’s sitting on my finger and no it didn’t bite me. They can be up to 25mm long (that’s one inch) and 50mm across the wings – a massive fly and the largest dipteran in Europe (I think it was bigger! Having measured the Ranger’s finger, the fly could’ve been at least 30mm – The Cat). Horseflies are big, fast-flying creatures, and they will bite any big mammal, including humans. The bite is very painful, and as horseflies cut the skin when they bite (rather than pierce it), horsefly bites can take a long time to heal, and can cause infection. Unlike insects which surreptitiously puncture the skin with needle-like organs, horse flies have mandibles like tiny serrated scimitars, which they use to rip and slice flesh apart.”

Hi Daniel
Thank you for getting back to me, and for your detailed description, it is very helpful.
Best wishes
What's That Bug? does not endorse extermination

Subject: Tabanus sudeticus
Location: Parkhill Inclosure. The New Forest. Hampshire
June 27, 2017 9:55 am
Hi. I have some pictures of a male Tabanus sudeticus, from The New Forest. What I’d like to know is – has the fly secreted this liquid? It didn’t seem to be feeding on it as I approached & didn’t move at all when I was taking photos. Thank you in advance.
Signature: Teresa

Male Horse Fly: Tabanus sudeticus

Dear Teresa,
Thanks for sending in your images of a male
Tabanus sudeticus.  According to Influential Points:  “Males of Tabanus sudeticus (not shown here) have the abdomen extensively yellow-orange. The facets in the upper two thirds of the compound eye of Tabanus sudeticus are, with the exception of those on hind margin, at least four times the size of the rest. ”  We know that many insects secrete fluids when they emerge from the pupal stage.  Your male Horse Fly is in prime physical condition.  Perhaps he just emerged and secreted fluids, and you took his images before his first flight.

Male Horse Fly: Tabanus sudeticus


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Subject: Beetle Moth Fly Thing
Location: Colorado
June 20, 2017 12:23 am
I came across this bug when I was walking my dog in a field and I’ve never seen anything like it before. It’s summer here and the bug was a little over an inch long. Any ideas??
Signature: Curious

Female Western Horse Fly

Dear Curious,
This is a female Western Horse Fly, identified by the gray thorax and the space between her eyes.  Only female Horse Flies are blood suckers, and though humans are not a normal host, a hungry opportunistic female Western Horse Fly might bite a person if no livestock are available.

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Subject: Is the green horsefly rare?
Location: Vinton Louisiana
May 7, 2017 8:11 pm
I came home this evening to find what I thought was a cool lightening bug in my kitchen buzzing around the ceiling fan. However, upon googling it, found out it was a horsefly.
I am 42, have traveled to nearly half the states in the US and have never encountered one that was totally green.
I live in Vinton Louisiana.
Are they rare? Are they indigenous to a specific area & if so where is that area? Are they a new insect?
All information is welcome
Thank you for your time.
Signature: Tova

Green Horse Fly

Dear Tova,
Green Horse Flies,
Chlorotabanus crepuscularis, are not especially rare, though they might have very localized populations in their range.  According to BugGuide:  “Body pale green, eyes and thorax yellowish green. The only green tabanid in NA.”  So they are not rare, but they are unusual.  The large eyes indicate that your individual is a non-biting male.  Here is a map of the sightings reported on BugGuide.

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Subject: ID Please
Location: East London, South Africa
February 12, 2017 11:52 am
I received a mobile photo of a rather large fly-like insect that I’m trying to identify for interest sake.
I have attached 2 cropped shots (sorry for poor quality) of the insect. It’s eating on a piece of apple, and a regular house fly can be seen in the background.
The photo was taken in East London, South Africa. Climate is coastal hot and humid.
I’d really appreciate it if you could try ID it for me please.
Many thanks
Signature: Kevin Durst

Male Horse Fly

Dear Kevin,
Because of the large eyes, this Horse Fly in the family Tabanidae can be sexed as male.  We found a similar image on iSpot, but it is only identified to the family level.  Female Horse Flies are blood suckers that commonly trouble livestock, and will bite humans if no four legged hosts are available.  Males only feed on sweets, mainly from fruits and nectar from flowers.

Hi Daniel,
Thank you for such a quick response, and for your identification and information…I really do appreciate it.
I asked on a Facebook page dedicated to insect I.D. too, and it’s confirmed as Tabanus biguttatus, known locally as a Hippo Fly.
Best Regards

Thanks for the species name assistance Kevin.  We actually have a well-researched Hippo Fly posting in our archives.

What's That Bug? does not endorse extermination