Say Hello to the Robber Fly
Paulette Greenberg, Anoka County Master Gardener Intern
Say hello to the robber fly, a member of the Alisade family; he certainly is not cute. If you come across one in your garden, you will be tempted to run for your life, or at least feel your heart skip a beat. The robber fly is one of the less celebrated members of the predatory insect community, but if you are lucky enough to see one, you should be thinking about ways to make it a more frequent visitor to your garden.
There are over 1,000 types of robber flies in North America. Some of them are known to eat Japanese beetles, but others will also eat honeybees and butterflies, which may be why they are not always recognized as garden heroes. According to Whitney Cranshaw and David Shetlar in their book “Garden Insects of North America,” while they can vary in size and color, most robber flies will have large eyes, an elongated abdomen, and a beaklike mouthpart usually hidden by a moustache. It may not win awards in the cute department, but a robber fly stalking and striking its prey from the skies is beautiful in its efficiency and speed.
They are opportunistic creatures and will patiently bide their time in a very conspicuous place, usually out in the open, to await their prey. Once the robber fly snatches its prey out of the air, it will inject it with digestive saliva and carry the hapless victim back to its favorite perch, where it will leisurely finish the meal. Just about anything winged is fair game for this hunter, and for those of us in Anoka County, we most appreciate its voracious appetite for mosquitos and grasshoppers.
Robber fly saliva is full of enzymes that help it digest the insects it catches; this allows it to convert its food from solid to liquid, because robber flies cannot digest solids. However, this neat biological capability will also make a robber fly bite very uncomfortable for a human. Do not try and handle these winged warriors; their bite packs quite the punch, resulting in swelling and irritation in addition to the large hole the proboscis creates in your skin. If one happens to land on you, the best way to handle the situation is to brush it away gently.
How do you encourage these unsung heroes to visit your garden or yard? Each species has its own preference for the ideal hunting ground but creating perching spots where they can catch some rays and look for their next meal is a good start. The robber fly feasting on a mosquito in the photo was a frequent visitor to the martagon lily buds in my south-facing border last July for a few weeks. Once the lilies bloomed, I didn’t see it again, so I decided that this year I will be planting more tall lily varieties that bloom at different times to encourage robber flies to visit more often, and perhaps stay the whole summer.
You can learn more about robber flies here:
https://nature.mdc.mo.gov/discover-nature/field-guide/robber-flies
http://entnemdept.ufl.edu/creatures/beneficial/flies/robber_flies.htm