Robber flies are named after their ability to rob insects of their lives in mid-air! But which insects do they attack? What do robber flies eat? Let’s figure it out.
There are around 7,000 species of robber flies in the world, and nearly 1,000 of them are native to North America.
Robber flies are one of the most fascinating creatures in the insect kingdom. They are known to be excellent hunters.
These little bugs can catch prey in mid-air, pouncing on unsuspecting bugs that happen to fly past them. In this article, we will talk about what robber flies eat and why this might be beneficial to humans.
What Do They Eat?
Robber flies (order Diptera, family Asilidae) are excellent hunters and usually prey on smaller insects, but they are also seen attacking insects bigger than themselves. In fact, adult robber flies eat anything that they can hunt.
Robber flies can also be cannibalistic and larger ones are often seen hunting and eating smaller robber flies. Let us look closely at what they eat.
Adults
Adult robber flies mostly hunt smaller insects like flies, ants, and more. But they will not hesitate to hunt down bigger insects like honey bees, dragonflies, and butterflies if they get a chance.
The insects they usually hunt are beetles, flies, moths, wasps, ants, crickets, grasshoppers, lacewings, and mayflies.
The adults will also pursue other smaller species of robber flies. These flies will also attack humans in the act of defense if they try to threaten them or mishandle them.
Larvae
There is a limited amount of data about what the robber fly larva eats.
One of the prime reasons behind this is that these creatures live in places like decaying wooden logs or soil, which are hard to access.
The only known info is that these larvae eat prey like grasshopper eggs and beetle larvae.
How Do They Hunt?
Robber flies live up to their other name – assassin flies. They are great hunters who often stalk innocent insects passing by an area from a vantage point.
Once the time is right, they pounce on the prey and inject them with their saliva using their long proboscis (needle-like mouthpart insects use to suck things).
The saliva contains neurotoxic enzymes that paralyze the target. It also contains proteolytic enzymes and other digestive enzymes that liquefy the inside organs of the hunt.
One fascinating thing about their hunting behavior is that they usually carry the prey back to their territory before consuming it.
Once they enter their zone, they rest on the branch to feast on their meal.
In the case of smaller prey, it can take around 5-15 minutes to finish off the meal; for the heavier targets, it can take up to an hour.
Adaptations That Help Them Hunt and Eat
These agile hunters have evolved several features that help them to hunt efficiently.
They are equipped with strong legs, spiky bristles on their body, a long and sharp proboscis, and large compound eyes.
Let us look at these features in detail below:
Proboscis
The proboscis is one of the primary weapons that a robber fly uses to hunt. It is a dagger-like beak that acts both as a weapon for impaling and as a straw for eating their food.
The flies use the proboscis to inject saliva into the prey, which paralyzes them. Once the target is paralyzed, they inject digestive enzymes that liquify the internal tissues of the hunt.
These digestive enzymes do not damage the outer skeleton of the body, but make it easy for them to suck out the juices.
Once the flies carry the kill to their territory, they use the proboscis to suck the liquid and complete their meal.
Bristles Around The Mouth
If you look closely, you will notice a good bunch of bristle-like hair on their faces (known as mystax) between the eyes and mouth.
Since they are active hunters and are seen hunting larger prey, these bristles protect the flies from receiving facial damage from the struggling insects when they inject the saliva and impale the prey.
Several Eyes
Here is one of the most intriguing facts about robber flies, they have more than two eyes. Yes, you read it right!
Although you may only notice a large pair of eyes on these flies, they do have three simple eyes located on the top of their head in a wedged area between the two big eyes.
These extra eyes help them to find their prey better and to detect danger in the area that normal eyes can’t.
Strong Legs
Since these insects often carry their prey back to the territory to eat them, they need a strong pair of legs to help move the weight of heavier insects like dragonflies and bees.
The legs of robber flies are spiny but tough, and they help them carry weights much larger than themselves.
Lifecycle
The female robber flies lay eggs in areas and plants that are close to the ground or in some corner of a wooden log.
When these eggs hatch, the larva comes out and lives and grows in soil or in decaying wood.
These larvae are also predatory in nature and are often seen eating eggs of pest insects like grasshoppers and beetles.
During winters, robber flies overwinter in the soil as larvae or by transforming into pupae. They come only out of the soil once the temperatures are higher, and they can find ample food for themselves.
Are They Beneficial?
These flies will consume any insect that they can kill, which means they will remove pests and other beneficial insects like white grubs from your garden.
Also, while they are capable of inflicting pain through their bites, they are great hunters of pests like grasshoppers, beetles, and more.
These flies are like a mixed blessing to the farmers, as they are capable of killing beneficial insects but also removing almost all unwanted pests from the garden.
How To Invite Them To Your Garden
Robber flies are omnivorous creatures. Although the central part of their diet consists of insects, they drink nectar from the flowers.
So if you want to invite these beneficial insects to your garden, try planting more and more flowers. Both smaller and larger robber flies will be attracted to flowers for the nectar.
Frequently Asked Questions
Can robber flies bite humans?
Yes, robber flies are capable of biting humans. Due to the digestive enzymes and venom present in their saliva, they are capable of delivering painful bites, so humans must be careful around them. These flies won’t attack a human until they are threatened or manhandled.
What are robber flies attracted to?
Robber flies are highly attracted to areas that get plenty of sunlight and are full of flowering plants. Such sites are usually full of robber fly prey.
They are also great sources to obtain nectar that supplements their majorly carnivorous diet. So if you want to invite these flies to the garden, make sure it is filled with good flowers and plants.
Do robber flies eat mosquitoes?
Robber flies are superlative hunters and are known to consume any insect that they can hunt.
The list of prey includes everyone starting from mosquitos, flies, beetles, butterflies, moths, ants, wasps, bees, and more.
Larger robber flies are also known to consume their smaller cousins!.
Are robber flies aggressive?
Robber flies are aggressive in hunting and are known even to kill and consume insects that are bigger than them.
They are usually not aggressive towards humans until they are threatened and mishandled. One should not approach these flies recklessly as they are capable of providing extremely painful bites.
Wrap Up
Robber flies are fascinating creatures with unique bodies and a thirst for the hunt like no other. These silent assassins of nature can quickly wipe out an entire garden full of bugs.
Knowing about these creatures will help you understand them and handle them better. We hope this article provides all the necessary information about these flies.
Thank you for taking the time to read this article.
s
J
.
39 Comments. Leave new
Thanks for posting this. I noticed that the japanese beetles seemed to have disappeared and I have a thriving population on what I thought were bumble bees on steroids. I hope they come back next year as I am sure the japanese beetles will be back. Both bugs seem to love marigolds
Actually it looks much closer to Diogmites angustipennis
Link on BugGuide for reference… http://bugguide.net/node/view/72787/bgpage
I’ve notices these here in Central Texas lately-perhaps something to do with the extreme drought lately? I haven’t seen them much before, in wetter years at least.
This is the yellow-bellied bee assassin, Apiomerus flaviventris, fairly common in Arizona.
You are correct that this is Apiomerus flaviventris.
You are correct that this is Apiomerus spissipes, a common species in Texas.
You are correct that this is Apiomerus spissipes.
Yes, this is Apiomerus spissipes.
Yes, this is Apiomerus floridensis.
Thanks for the quick response !
where can i get this genus Laphria Robber fly, i have so many Japanese Beetles coming out its unbelievable. Can I buy this fly somewhere, I live in northern virginia.
To the best of our knowledge, Robber Flies are not available commercially.
Hi there, Dori! I was in Yellowstone and Grand Tetons at almost the same time you were, and also saw some of these robber flies. I was always glad to see them hanging around, because they provided some measure of protection against the numerous biting flies. In fact, once I was sitting outside and a robber fly decided to use me as a base of operation, perhaps because my presence was drawing in nasty bloodsucky things. Every time a biting fly buzzed nearby, the robber fly launched itself off its perch on my leg and went chasing after it. I didn’t get bitten even once that evening. Anyway, thanks for bringing back memories for me! Hope you had lots of fun on your trip.
This is an awesome shot!
This is an exciting find. This is not a Laphria, but rather, Dasylechia atrox, a very rare asilid known from just a few dozen specimens.
Wow, thanks for letting us know. We will update the posting. Upon checking BugGuide, we see that our posting is roughly contemporary with the first posting there. We wish we would have know the significance of the sighting in 2011 when we posted and featured this individual.
So it’s a robber fly and not a bee at all! Thanks for clarifying. All I knew was that I wanted more of them, flying around with Japanese beetles in their maws! Now I just need to figure out how to improve habitat for them…
Cheers,
Tripp
So it’s a robber fly and not a bee at all! Thanks for clarifying. All I knew was that I wanted more of them, flying around with Japanese beetles in their maws! Now I just need to figure out how to improve habitat for them…
Cheers,
Tripp
I am curious about the Carpenter Bee Robber Fly on your website. Are they found in the United States? I had 2 of what looked like these fly into my hen pen today and one laid eggs on some greenhouse plastic being stored in there. I live in San Antonio, TX and have now seen 3 of these for the first time ever just this year. They do not appear to be aggressive as I took photos only a couple feet away.
We have numerous Robber Flies in North America, but the Carpenter Bee Robber Fly is not found in North America. If you send your images using our Ask What’s That Bug? link, we can try to identify your individuals.
Had my first encounter with a giant robber fly yesterday. It was huge. I didn’t know what it was. I had never seen anything like it. Great article here. Good read!!
It looks to me like it can be an Apiomerus species simmilar to A. crassipes http://bugguide.net/node/view/656610/bgpage
Thanks Cesar. That could be correct.
I am the original poster, and I think the photo at your link looks the most like what my husband killed in our home. We have noticed a large number of bumble bees around our home this spring. Are these bugs dangerous to humans? I will sleep a lot better tonight if your answer is NO! Thanks!
Your question has us a bit confused as you mention several insects. Kissing Bugs might be dangerous if they are carrying Chagas Disease, though that possibility is not too great in the U.S. Chagas tends to be a bigger problem in the tropics. Kissing Bugs may bite and the bite may cause localized pain and irritation. The same could be said of Apiomeris species, Bee Assassins, but in their case, there is no danger, just pain and irritation. Stings from Bumble Bees are not common, and they might be dangerous if a person has an allergic reaction.
Oops! I was so excited that the bug we found could be something other than a blood sucking cone head bug that I wrote my reply in too big a hurry and didn’t re-read it to make sure it made sense before I sent it! After looking at the link from Cesar, and comparing we have decided that it is a bee assassin. It makes sense because we have noticed a large number of bumble bees in our yard this year so there’s plenty of prey for it. I’m so relieved that the bee assassin prefers insects as prey and that we and our dog aren’t the primary targets for a meal! I hope we never see another one inside our house and if we see any outside we will leave them alone so that we won’t risk getting a painful bite. Thank you for this site and for your answers!
We will correct the posting with the identification Bee Assassin.
It was pretty small. I would say your 5mm is about right.
Suddenly, they are all over my wife’s garden and seem to enjoy dining at the edge of day-lily petals.
Also, once they have something to eat, they stay put long enough to line up a nice shot. I used a macro lens that required getting about two inches from the subject with a flash held six inches above, and got several shots. I’m wondering if its brain doesn’t have enough circuitry to flee and eat at the same time.
Thank you! It is good to know that we were at least in the right general area for an identification even if we didn’t get it quite right. We had noticed that the black and yellow color pattern seemed reversed, but we had not found anyone with our guy’s pattern.
Thanks again for all the work you do.
Thank you! It is good to know that we were at least in the right general area for an identification even if we didn’t get it quite right. We had noticed that the black and yellow color pattern seemed reversed, but we had not found anyone with our guy’s pattern.
Thanks again for all the work you do.
I also have witnessed a similar event while working as an Avian point count tech. in South central PA around Bedford.
Just saw one in my garden in Ravena, New York! I have also noticed a decline in Japanese beetles this year!
Hi Bugman,
I’m a robber fly researcher tracking down online records for a little paper I’m writing about the fairly rare species Dasylechia atrox. Among other things, I’m compiling the new data available if we consider “records” shared on insect social media, and so I’m hoping I could get permission to include this picture in my paper. I’ll include a weblink in the “specimen” list, but I think including the actual pictures will help legitimize the metadata of non-lethal observations like these– since there are no physical pinned specimens to serve as vouchers, the images themselves are the data and should be entered into the permanent record so future people can double check the IDs. I’m not sure if you have a way of contacting the original photographer Jessica but I’d like to credit the creators, and can send you all a PDF copy of the paper when it’s all done if you like.
Thanks!
Hi Tristan,
Unfortunately, after seven years, we are not able to contact Jessica. What’s That Bug? reserves the right to publish images and information submitted to our own site and to scientific publications that request permission. We will email you the images, but alas, they are small digital files. One of the reasons we requested you to place your request as a comment on this posting is that in the event Jessica researches her submission, there will be a record for her. Please credit Jessica of Royal Oak, Michigan, and courtesy of What’s That Bug? with our web address.
I was bitten by a bug yesterday in scotland and have a pictute of it. I will tgy to get it on hrre.
I just found one of this species. It for first I see it.what are they doing in nature. I just to have knowledge of them too
i saw this today in the garden. i was very excited about it and now know that was robber fly and not a bumblebee. Are these flys dangerous to beneficial insects? We keep honeybees. Should we worry about these robber flys? Of course DELIGHTED to have an ally against those damn beetles.
Many Robber Flies prey on Honey Bees.
I saw this at my house in florida!!!