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iNaturalist observation of the month: Robber fly

By Patricia Simpson | iNaturalist

Earlier this year, on the trail, I was startled by a deep buzzing sound followed by a large fast flying insect zipping right in front of me. A wasp maybe. Seconds later, I could see the long slender-shaped insect resting on a rock.

Robber Fly (Photo by M. Basden)

As I approached, I was surprised to see a rather large fly with its single set of wings neatly folded over its back. Bulging brown eyes, triangular face with a beak-like appendage, long spread-out legs, a slender abdomen and a white beard! For sure I was looking at a robber fly, though I had never seen one quite so large.

Others have been documenting robber flies in Mission Trails Regional Park this summer, such as in this iNaturalist observation by klyle161 at bit.ly/2zJNeyW.

I was able to get close to the robber fly by moving very slowly. The beast and I observed each other, though it lost interest in me quickly, being far more preoccupied with its next meal (fortunately, none of us are on the menu!). Its head moved very quickly (lightning fast, really) as it looked around at any moving insect that might dare get close.

The robber fly is a fierce predator. Its keen eyesight allows it to detect small insects at a fair distance. The fly will take flight and catch its prey “on the wing” (meaning in mid-flight). Once the meal is secured, the robber fly finds a resting spot and consumes the victim after injecting liquifying saliva into it. Bon appetit!

Robber flies catch a large array of insects including some almost twice their size. They are also undeterred by predators such as wasps or bees and often add them to their menu.

Despite all that, don’t let their appearance scare you away. They will not come after you. But do not handle them as they have a nasty bite! Enjoy watching them from as close as you can get … they’ll get scared before you do and just fly away.

For more on this fascinating animal, enjoy this little video by MikeBlairOutdoors at bit.ly/2Otlh6v.

—Patricia Simpson is a trail guide at Mission Trails Regional Park.

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