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

Six Years ago today we originally posted this exciting submission.

Ed. Note:  February 21, 2014
It has just come to our attention that this is one of the rarest North American Robber Flies,
Dasylechia atrox, and more information can be found on BugGuide.

Carnivorous bumble bee?
Location: Royal Oak, MI
August 2, 2011 2:15 pm
We have a honey bee hive in our yard and have been very bug friendly. We have cicada killing wasps in our driveway and we just steer clear of them instead of filling it with concrete.
Imagine my shock when I was hanging laundry out and saw one of our honey bees having the life drained out of it by what appears to be a bumble bee. Is it?
Signature: Jessica

Rare Robber Fly: Dasylechia atrox eats Honey Bee

Hi Jessica,
We absolutely love your email, and we would like to wax poetically after we answer your question.  This is a Robber Fly.  It is one of two genera that both feed on large flying insects including bees and wasps that are captured on wing.  Robber Flies are amazing hunters.  They do not sting.  They will not attack you and bite you, but they might bite you if you tried to pick one up, though we could not imagine how you would ever be able to catch one.  We cannot, based on your photo, determine if this is a Bee Killer in the genus
Mallophora, or a Bee-Like Robber Fly in the genus Laphria.  One of the ways they can be distinguished from one another is the shape of the antennae.  Your specimen appears to have antennae that end in fine filaments, a sign it is a Mallophora, however, upon enlarging the photo to better examine the details, your photo is not of high enough resolution to maintain image quality.  Your individual does not have markings similar to any of the five species represented on BugGuide, which makes us wonder if it might not be a Laphria, and based on the photos posted to BugGuide, there are several species with markings similar to your individual.  They seem to all have yellow beards, and it is not possible to make out the beard on your Robber Fly, though we are not sure if the black hairs are lost in the shadow or if the tasty Honey Bee meal is obscuring the beard.

Robber Fly eats Honey Bee


August 3, 2011
Hi again Jessica,
We are positively enthralled by the way you set the tone for your question by providing us with your bug friendly qualifications.  We would like to take additional time to comment on your mention of Cicada Killers.  We have devoted considerable internet real estate on our site toward lobbying for the preservation of Cicada Killers, and when we receive post-mortem images of them, we tag them as unnecessary carnage, but the fact of the matter is that we have never had to share our homes and yards with them.  We really cannot claim to have experienced first hand the communal nesting habits of these large wasps.  We applaud you for your tolerance and also for inquiring about this Robber Fly.  Since we began working on this posting, we have received another unidentifiable image of a large Robber Fly feeding on a Japanese Beetle, and the person who submitted that image wants to know how to encourage more of them.  These large Robber Flies are reported to be able to consume large quantities of Honey Bees, and for that reason, they have a bad reputation among bee keepers.  Thanks again for your wonderful submission.  

Thank you so much for the information. We try not to have knee jerk reactions to what we find in the yard and as the cicada killers are nonaggressive unless you happen to be a cicada, there was no reason to destroy their habitat. It’s a short two month inconvenience of my daughters running to the door from the driveway while screaming.
As for the robber flies, they may be a bit of a bother as we are beekeepers. We have already lost one hive to varroa mites a couple of years ago and would rather not lose another one. Now that I think about it, we have spotted a few smaller species of robber flies in our yard. We have never had these insects in our yard before. Do you think the beehive may be attracting them? Is there any way to humanely deter them from eating my bees?

Hi again Jessica,
We have no advice regarding the deterring of Robber Flies.  The smaller Robber Flies are most likely not preying on your bees, and the larger Robber Flies will not enter the hive.  They will attack individual bees that are in flight.  Good Luck.

Ben Coulter says:
What's That Bug? does not endorse extermination

Subject: Robber Fly species ID please?
Location: Merrimac MA
July 30, 2017 8:07 pm
Attached is a photo of a Robber Fly in our yard in Merrimac, Massachusetts in July, 2017. We would like to know what species it is. We had never seen one before, but we are only about 30 minutes from Reading, MA where evidently the mail trucks seem to be a favored spot to hitchhike!
Thank you!
Signature: Bonnie

Robber Fly: male Efferia aestuans

Dear Bonnie,
This looks to us like a male
Efferia aestuans, and according to BugGuide: “The most likely robber fly to land on humans.”

What's That Bug? does not endorse extermination

Subject: Is this a robber fly
Location: Princeton NJ
July 30, 2017 4:37 pm
I have never seen a fly like this. It’s about an inch long. I tried to find it on the Web, but the closest thing I could find is a robber bug. Is that what it is?
Signature: Barbara

Robber Fly

Dear Barbara,
Thanks to this BugGuide image, we are confident your Robber Fly is a male
Efferia aestuans.  According to BugGuide:  “The most likely robber fly to land on humans. (comment by Herschel Raney)  Sometimes fearless. The males are much less common and harder to approach. (comment by Herschel Raney)  The commonest species of Asilinae in the northeast (comment by Herschel Raney).”

Thank you Daniel. Are these beneficial insects, are should I kill these when I see them. I accidentally squirted it with the hose, and it just sat there looking at me. With insects, I try to identify them if they are new to me. I’m an organic gardener, and I rely on benefical insects.

Hi again Barbara,
Robber Flies are beneficial predators.  While they might bite a person if carelessly handled, they are not aggressive.  We do not condone killing Robber Flies.

Thank you! If I ever see it again, I will let it be. We have honey bees, but we can spare a few. We also have hummingbirds and hummingbird moths. Hopefully the robber fly will not bother those.
Thanks again. I really appreciate your service.

We believe your hummingbirds and moths will be safe as they are probably too large for this species, however we do understand that large Robber Flies can attack hummingbirds, something you can read about on Hilton Pond.

What's That Bug? does not endorse extermination

Subject: What is this?
Location: Media, PA
July 30, 2017 6:00 pm
I have never seen this type of bug before! It stood really still for a very long time, even as I was taking it’s picture, and then it flew away, like a helicopter!
Signature: Curious

Hanging Thief

Dear Curious,
This impressive, predatory Robber Fly is known as a Hanging Thief.

What's That Bug? does not endorse extermination

Subject: Mail truck invading bug in Massachusetts
Location: Reading, Massachusetts
July 29, 2017 7:04 am
So my boyfriend is a mail man in Massachusetts and he keeps getting invaded by these odd looking bugs. We’ve never seen them before but apparently all his mail man friends are having the same hitchhiker bugs in their trucks as well. Help what is it?!?!?
Signature: Mandy (singing mailmans gf)

Robber Fly

Dear Mandy,
This is a Robber Fly in the family Asilidae, an aerial predator that catches its prey while on the wing.  We are unable to provide a species identification.  We don’t know why all the mail trucks in Reading, Massachusetts are being used by the Robber Flies as resting spots.

What's That Bug? does not endorse extermination

Subject: Identify insect
Location: Front Royal, Virginia
July 25, 2017 5:33 pm
Respectfully request an identification of this insect.
Thank you in advance!
Signature: Jean

Hanging Thief

Dear Jean,
This Robber Fly is known as a Hanging Thief because it dangles from one leg while eating prey captured on the wing.

What's That Bug? does not endorse extermination