Not as beautiful as other horseflies, e.g. Chrysops relictus, but much larger, really scary, is T. sudenticus. Happily, it was not nearly as nasty as C. relictus. This could be because our fly seems to be male – it has holoptic eyes, which means the eyes meet in the middle of the head. That makes them see 360 degrees – great to find a partner. Male horseflies feed on nectar, only females need blood to produce eggs, as mosquitos females do. In over 3000 (!!!) species of horseflies, there might of course be some exceptions. Find some more information about horseflies here.
Ok so here we have the heaviest (not the largest?) horse fly of Europe. What else? A lot! Read this paper to get the full horror. A study from France, where they looked at the effect of horse fly attacks on cattle. They caught almost 4000 flies in 6 days. 4 flies per minute (mean landing count!! – so mean!) landed on each cow. Different species preferred different body parts of the cows, and our species here was the only one to attack the back. Because Horseflies have a significant effect on the well-being (and thus productivity) of cattle (and I guess other livestock), there are lots of papers about how which and why they bite.
Knowing how much one single bity fly can ruin the day, I hope you farmers do everything you can to protect your animals from those flies! I wonder if the clingy jumping spiders could have a business opportunity here?!
BTW There is not too much known about the larvae, which seem to live in humid soil and are of course predators. I would love to see one in real!
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