Robber flies are predatory insects known for their voracious appetite and ability to feed on various arthropods, including wasps, bees, and dragonflies. These flies may seem intimidating, but they play a crucial role in maintaining a healthy balance between insect populations in different habitats. Yet, in some cases, they might become a nuisance and need to be managed.
There are several methods to get rid of robber flies in your garden or home. One effective approach is using traps designed to attract and capture these pesky insects. On the other hand, natural predators can also help to control their population, ensuring the protection of beneficial insects in your garden.
In the following article, we’ll discuss different methods of robber fly management and explore their pros and cons to help you make an informed decision. Stay tuned for more tips and information on effectively dealing with these intriguing predators.
Understanding Robber Flies
Characteristics and Size
Robber flies, belonging to the Asilidae family, are medium-sized to large, bristly, or hairy flies found in North America. They are often confused with biting flies but are not blood feeders.
- Pointy, knifelike proboscis (mouthparts)
- Bearded face
- Long, tapered abdomen
- Humpbacked appearance
- Spiny legs
- Brown, gray, or black coloration
Robber flies can vary in size, with some reaching lengths of up to 1.5 inches.
Comparison table between Robber Flies and Biting Flies:
|Forms of attraction
|Insects as prey
|Attracted to human/animals
|Benefit to humans
Biology and Life Cycle
Robber flies are predatory flies that perch in open areas and swivel their heads to search for insect prey. They tend to ambush their prey by pouncing on them from midair. Their life cycle includes the following stages:
Robber flies are considered beneficial predators, as they help control other insect populations by feeding on pests such as mosquitoes, beetles, and grasshoppers.
Natural Predators and Benefits
Role in Ecosystem
Robber flies are a beneficial predator in various ecosystems, such as grasslands and forests. They help maintain the balance in the ecosystem by preying on numerous insect pests.
Preying on Pests
Robber flies attack and consume several pest insects, including bees, wasps, and other flies. This significantly reduces infestations and protects plants from pest damage.
Key features of robber flies:
- Efficient pest predators
- Control various insect pests
- Contribute to maintain ecosystem balance
Pros of having robber flies:
- Reduces pest infestations
- Minimizes plant damage
- Lowers the need for chemical insecticides
Cons of having robber flies:
- Can sometimes attack beneficial insects like bees and wasps
Comparison table of robber flies and other predators:
|Bees, wasps, other flies
|Reduces pest infestations, protects plants
|Caterpillars, aphids, scale insects
|Biological control; parasitizes pest insects
By understanding robber flies and their role as natural predators, we can appreciate their benefits in controlling infestations in ecosystems and gardens.
Prevention and Control Measures
Sealing Your Home
Doors and windows: Ensure all doors and windows are well-fitted with screens to prevent houseflies and other flying insects from entering.
Weather stripping: Apply weather stripping to gaps around doors and windows to further deter robber flies from entering.
Reducing Attractive Factors
Eliminate standing water: House flies and flying insects are attracted to standing water, so ensure to keep drainage systems clear and remove any stagnant water from your property.
Properly store food and waste: Dispose of food waste in sealed bins and clean up spills and crumbs immediately. This helps to reduce fly-attracting odors.
Safe Fly Traps and Repellents
Fly traps and fly paper: These sticky, adhesive products can be hung near windows and entry points to catch flies without the use of harmful chemicals.
Essential oils: Some essential oils such as lavender, eucalyptus, and citronella can act as natural bug repellents to deter house flies and other pests.
While implementing these preventive measures, it’s important to maintain a balanced pest management approach. One method might not be able to completely control the issue, so it’s essential to combine the most relevant and effective options.
Natural Repellents and Solutions
Using Herbs and Plants
Robber flies can be deterred by certain herbs and plants.
For example, lavender, eucalyptus, and lemongrass are known to be effective fly repellents. Planting marigolds and other flowers can help keep these insects at bay.
Homemade Fly Traps and Sprays
You can create your own fly traps and sprays to deal with robber flies.
A simple trap involves apple cider vinegar, dish soap, and water. Mix these ingredients and place them in a container to attract and trap flies.
Another option is using a light trap or growing a Venus flytrap to catch these pests.
|Apple Cider Vinegar Trap
|Eco-friendly, easy to make
|May not catch all flies
|Effective in attracting flies
|Requires electricity, expensive
|Natural and attractive solution
|Only catches a few flies
Fly Repellents and Solutions to Try
- Basil: Planting basil around your home can help deter robber flies.
- Mint: Mint possesses strong aromatic properties that can repel flies.
- Cayenne pepper: Spraying cayenne pepper solution can deter flies from landing in certain areas.
- Citronella candles: These candles emit a scent that may help keep flies away.
By implementing these natural solutions, you can effectively minimize the presence of robber flies around your home and garden.
Tips for Maintaining a Clean Environment
Eliminating Food Sources
One key aspect of maintaining a clean environment is eliminating food sources for pests like robber flies. Some common food sources include:
- Dirty dishes: Always clean and put away dishes promptly.
- Garbage cans: Make sure to cover and regularly empty garbage cans.
- Animal feces: Dispose of pet waste daily.
Reducing these food sources can help deter pests such as fruit flies and maggots.
Managing Compost and Waste
Properly managing compost and waste materials can also help prevent robber fly infestations. Some important practices include:
- Compost piles: Make sure to turn and aerate compost piles regularly.
- Moisture: Avoid excess moisture to discourage breeding.
- Manure: Keep animal manure well maintained and contained.
By effectively managing compost and waste, you also help prevent issues related to unwanted pests like maggots.
Pet Care and Hygiene
Proper pet care and hygiene contribute to a cleaner environment and reduced risk of robber fly infestations. Some crucial aspects of pet care include:
- Regular grooming: Keep your pets clean to avoid attracting flies.
- Pet feces: Clean up pet waste daily to prevent attracting pests.
- Debris: Remove any debris or clutter in your pet’s area.
By following these tips, you can create a cleaner environment, preventing robber flies and other pests from becoming a problem.
Health Risks and Concerns
Diseases Carried by Flies
Robber flies might be mistaken for biting flies, but they do not feed on blood and generally do not pose a threat to humans. However, other types of flies, such as the common housefly (Musca domestica), can carry and transmit various germs and diseases. For example:
- Dysentery causes severe diarrhea and can lead to dehydration.
- Cholera is a bacterial infection that causes severe watery diarrhea and dehydration.
- Typhoid fever is another bacterial infection that presents with fever, headache, and abdominal pain.
These diseases are mainly transmitted when flies contaminate food, water, or surfaces with bacteria.
Precautions to Avoid Infections
To protect yourself and your family from infections caused by flies, follow these precautions:
- Keep food covered and stored properly to prevent fly infestations.
- Regularly clean and dispose of trash to avoid attracting flies.
- Reduce moisture around your home, as this can attract flies and promote the growth of larvae.
- Use insecticides or light traps to keep flies at bay.
- Install fly screens on windows and doors to prevent flies from entering your home.
By taking these measures, you can minimize the risks associated with flies and maintain a healthy living environment.
Professional Assistance and Treatment
When to Call Pest Control
Sometimes, robber flies become a nuisance, and you may need professional help. Call pest control when:
- Robber flies are found in large numbers
- Their presence leads to distress or potential health risks
For example, pest control may help eliminate horseflies, a biting fly often mistaken for robber flies.
Chemical Treatments and Safety
Several insecticides can be used against robber flies. Some popular options are:
- Pyrethrin: An organic compound derived from chrysanthemum flowers
- Synthetic pyrethroids: Chemicals that mimic pyrethrin’s insecticidal properties
These treatments may have benefits and drawbacks:
- Effective in controlling robber flies
- Can be applied on soil, appliances, and drains
- Can be toxic to beneficial insects and other non-target species
- Prolonged exposure may lead to soil contamination
Flytraps and Ultraviolet Light
An alternative to chemical treatments is using flytraps or ultraviolet (UV) light devices. These methods can help catch and control robber flies without chemicals:
- Flytraps: Devices that lure and trap flies using attractants like colors or scents
- UV light devices: Emit ultraviolet light, attracting and zapping flies upon contact
Here’s a comparison of these two methods:
|May not catch large quantities
|Can be used indoors or outdoors
|May attract beneficial insects
|Can be harmful to humans’ eyes
|Requires electricity source
Choose the method that suits your needs and environment. Remember to follow safety precautions when using insecticides or UV light devices to control robber flies effectively and responsibly.
Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.
Letter 1 – Unnecessary Carnage: Smashed Robber Fly
What is this bug?
Location: Sacramento, California
October 1, 2011 4:16 pm
I saw this in my yard. I smashed it because it had what looked like a stinger.
As it died the stinger was going in and out. Ick. What is it?
Robber Flies are harmless, beneficial predators, and smashing them constitutes Unnecessary Carnage in our minds. We believe this may be a member of the genus Andrenosoma based on photos posted to BugGuide. What you have mistaken for a stinger is probably the ovipositor, the organ the female uses to lay eggs.
Letter 2 – Robber Fly probably False Bee Killer
Subject: ZZtop Fly that just sat there
Location: Dallas area Texas
July 16, 2014 8:34 am
Found this rather large fly on my car. He sat there for over a day in the hot sun. I set the P&S on macro and captured these shots. The white tip on his tail, and the lines aon his back should be distinctive. The hairy face reminded me of ZZ Top – a Billy Gibbons fly?
Any idea what this one is called?
Signature: Richard Todd
This is a predatory Robber Fly in the family Asilidae. Thanks to Bugs In The News, we believe we have correctly identified your individual as a member of the genus Promachus, the Giant Robber Flies, possibly Promachus bastardii. BugGuide tends to substantiate that identification. BugGuide indicates the common name for this species is the False Bee Killer. Bugs In The News also provides this information: “Robber flies are equipped with a short, but strong proboscis which is used like a sword to pierce the integuments of their prey. The proboscis is further equipped with an orifice, distally, through which salivary secretions are injected into the prey. These secretions contain neurotoxic enzymes that paralyze and incapacitate, and proteolytic enzymes that digest animal tissue. Once the robber fly attacks and subdues its prey (which often includes insects of its own family, and even its own species; robber flies are notorious as true cannibals), it remains attached via its proboscis until the prey’s internal tissues have been digested to a liquefied state, whereupon it sucks the ‘nutritious’ (!) liquid up through the same orifice that delivered its salivary secretions, to consummate its grand, though — from a human perspective — disgusting, feast.”
Letter 3 – Robber Fly, killed with a shoe out of fear
Strange Wasp Flew into Home. Never Seen before!
August 7, 2009
Hello. I was recently helping move furniture out of my basement to help my sibling move out, and as I was returning through the door a massive dark bug flew in front of me and came inside. The bug was very large, about 2 inches long, and it made very loud buzzing. It landed on our ceiling lights, so we left the door open and turned off the lights hoping it would leave. Unfortunately, it decided to fly onto my mother, and fearing that it would sting her, we had to kill it with a shoe. Though the bug has been squished, I’m hoping I had reasonable cause to kill it and am hoping you can identify it. It had two wings, the body was entirely dark with no yellow, and the long abdomen was black with brown stripes. I have lived in Southeast Tennessee for 10 years and neither I nor my parents have ever seen a bug like this. Please let me know if you can figure it out!
This is a Robber Fly in the family Asilidae, and they do not routinely attack humans, though if carelessly handled or threatened, we suspect they might bite. We fully understand your fear and the reaction that caused you to squish this Robber Fly with a shoe, and we intend no malice in our assessment of Unnecessary Carnage. We do not intend to imply that you are evil because of your instinctive protective action, and we hope that this will educate you in the future should you ever again encounter a Robber Fly. Robber Flies are important predators and they should not be killed. We are trying to use caution in our choice of words because we have recently been accused of libel and malicious intent and defamation of character after performing a free public service and identifying dead insects that we thought were killed unnecessarily and then posting the responses. It has always been our intent to educate people and not to chastise.
The querant responds
I just don’t see the necessity to “file it under Unnecessary Carnage”. You guys are creating this problem for yourself when you could just leave it well enough alone. A simple suggestion would suffice, such as saying “They aren’t typically a threat, so please refrain from killing them.” instead of making every single person look like a criminal. A large and scary looking insect on somebody you love is a well enough reason to kill it, and condemning somebody for it is not my idea of rightful. Unfortunately, I agree that you’re violating your 1st amendment rights and committing libel, but hopefully whoever is suing you has lawyers that can reveal it better than I can.
“A large and scary looking insect on somebody you love is a well enough reason to kill it” is precisely the reason it needs to be filed under Unnecessary Carnage. Just because something is scary looking does not mean it is harmful and if every scary looking thing is killed, there might soon be nothing left on the planet. Some people might even be scary looking. Calling an act unnecessary is not a libelous statement. Criminal is your word, not our word. While we maintain that we bear no malice towards people who kill insects because they don’t know any better, it seems as though the statement “Unfortunately, I agree that you’re violating your 1st amendment rights and committing libel, but hopefully whoever is suing you has lawyers that can reveal it better than I can” does contain a degree of ill will directed towards What’s That Bug? It does give one pause to ponder just who bears malice toward whom.
Unnecessary Carnage Comment
August 9, 2009
RE: unnecessary carnage
I love your site, and visit it several times a day. Many thanks for posting such lovely images and so much information (you helped me ID a one-eyed Sphinx moth here in Seattle)! I also love the fact that you tell folks when they have committed an act of unnecessary carnage, but sadly, you have been very hesitant to do so lately… Please don’t let one or two unhinged people keep you from providing a vital service- letting humans know that insects are innocent until proven guilty!
Letter 4 – Robber Fly in genus Ommatius
Possible Robber Fly
Thanks for taking the time to review my message. I saw this odd creature two mornings in a row and I was able to capture it (photographically) the second morning. Originally I thought it was a mosquito, however, now that I have found your site, I know I’m wrong. The closest guess I could come up with is that this may be an immature fly – possible a robber fly.?. I can say that s/he did not really appreciate the flash as I was allowed only one shot per sitting. This shot was taken 7/29/2006 @ 10:50 AM, in a rural suburb of Pittsburgh, PA. The image was obviously taken with a macro lens, and to frame the size, the brown object is the edge of a 4×4 post on my deck. Unfortunately, the image is a bit dark due to the small aperture used, and you can’t see the wings. The bug was small enough to be considered a female mosquito at first glance, so I think it is a little small to be a robber fly. Thanks again for your time, and the great work you do with this site.
Immature flies are maggots. Once the fly becomes an adult, it has reached its maximum size. This is a small species of Robber Fly in the genus Ommatius. We have lightened you photo using “level” in Photoshop.
Letter 5 – Robber Fly or Flower Loving Fly ??????
That is what it looks like in my insect book, BUT, it says they are in the west and I live in NE Arkansas. It was resting on a pole I am using to hold up some cone flowers. A stray, maybe? Think global warming is doing some strange things! It is also similar to the Flower Fly you have pictured. Is that the same thing? Thanks so much for a fantastic site. My only problem……I spend waaaay to much time here!
This is a Robber Fly and we have an entire page devoted to them. Guess you might spend some additional time reading our site now. They are a local species for you, but that does NOT DISPROVE global warming.
Good morning Thanks for your response. I guess my confusion comes in because according to the pics in my book, National Audubon Society, First Field Guide to Insects, it says it is not a Robber Fly, but a look-alike…Flower-loving Fly (Apiocera haruspex). The main difference I saw was that it didn’t have the bristles and it has that bulb like thing at the end of the abdomen. The robber flies that I have seen here do not have that bulb like thing. I know Robber Flies are common here, but I have never seen or heard of a Flower-loving fly and according to my book, they are found in the west. Bummer….thought maybe I had something unique in my yard! Still a cool looking lil dude! Thanks again for a fantastic site!!
Hi again Sandy,
Now we are doubting our original identification since you bring up a good point. We will check with Eric Eaton for clarification. Here is Eric’s assessment: “The robber fly in question is a male Efferia. They have the bulbous claspers, making them reasonably easy to identify.”
Letter 6 – Swatted Robber Fly
We had this flying around our work and finally killed it. What in the world is it?
Poor Dead Robber Fly. This is a beneficial insect that often kills and eats other pestiferous flies.
Letter 7 – Freaky Flyday Part 2: Unknown Robber Fly from Australia
Subject: A day of Freaky Flies
Location: Yarra Valley, Victoria, Australia
December 15, 2012 3:27 am
Hello Bugman, you’ve helped me before with a Bristle fly a couple of years ago. Today I’ve seen 3 strange flies on my cherry tree, which is currently being attacked by the cherry tree slug. I suspect they could be feeding on it, but I’m not sure.
It’s Summer here in Australia and today was a dull humid day.
Signature: Linda, Yarra Valley
Update: December 16, 2012
these are the best I could do. I hope they give you enough information to identify it. I noticed on the side-on shots a little white thing that looks like an egg on this fly. Is that normal anatomy or has it been parasitised? Just wanted to add, I didn’t harm any of the flies, they were all alive and well when I left them. The cherry tree slugs were another matter though.
Linda from Healesville
Thank you for sending the additional requested images. We originally thought this might be a Robber Fly and we maintain that opinion based on the beard visibly in the new photos. Alas, we have been unable to identify this Robber Fly to the species level. We believe the white object you refer to is a haltere, the vestigial wing structure of most flies. Flies are distinguished by a single set of wings, unlike most winged insects that have two pairs of wings.
Letter 8 – Robber Fly: Laphria saffrana
Subject: what’s this bug
Location: 1 hr north of Houston TX
April 29, 2014 6:17 pm
I only got one pic of this bug before it flew away, so it can fly. It has a very unique marking on the top of the thorax, huge eyes. Looks like a digging or stabbing beak. Hairy legs. this bug is between 1 1/2 and 2 inches long.
Signature: I don’t know the answer
And we are very happy you managed to get that one photo. This is a Bee-Like Robber Fly, Laphria saffrana. We identified this magnificent predator on BugGuide where it states: “Bromley (1934) considered this species to be a mimic of the queen of the southern yellowjacket, Vespula squamosa.” Laphria saffrana is also represented on iNaturalist.
Letter 9 – Robber Fly Swatted at Work
Subject: what is this thing I killed at work
Location: St. Louis, MO
July 10, 2014 1:06 am
this creature was flying around my head today at work. it must have gotten inside when a customer walked in the door. anyway, it flew like a wasp or maybe even a mosquito and it was about an inch or inch and a half in length. as soon as it landed where I could kill it, I didn’t hesitate. so I’m just curious as to what this thing is!
Even in its swatted state, this Robber Fly is a magnificent creature. Robber Flies are beneficial predators and they will not attack humans, though they might bite if carelessly handled. We believe your Robber Fly, a victim of Unnecessary Carnage, is a Hanging Thief.
Letter 10 – Robber Fly: Efferia species
Subject: What is this?
Location: Lynwood Calfornia
August 17, 2014 7:16 pm
Can you help me identify this bug? I found him outside my door step
Signature: Not sure
Dear Not sure,
This is a Robber Fly in the genus Efferia, and though we went through numerous images on BugGuide, we could not find any that have the exact coloration of your individual. You can compare your image to this image on BugGuide to see that the general physiology is the same. According to BugGuide, there are: “110 spp. in our area,” and “in our area, the vast majority are restricted to sw. US, with some widely western spp. and just two widespread spp.” According to Eric Eaton, male Robber Flies in the genus Efferia: “have the bulbous claspers, making them reasonably easy to identify.” Just as we were about to post, we discovered this image of Efferia antiochi on Sardis & Stamm about the Antioch Dunes National Wildlife Refuge that looks identical to your Robber Fly. According to the California Department of Fish and Game: “Known only from Antioch, Fresno, and Scout Island in the San Joaquin River” which would indicate it is not the same species, but is sure looks close.
We would strongly suggest that you contact the Los Angeles County Museum of Natural History as this might be a significant find.
Letter 11 – Robber Fly: Microstylum morosum
Subject: Giant flying bug with green eyes
Location: mid texas
June 3, 2015 12:46 pm
this is about the size of the whole palm of my hand. We are located in mid Texas and it’s the beginning of June! It’s been sitting in a pot for about 5 hours and hasn’t moved.
Letter 12 – Robber Fly: Microstylum morosum
Subject: Weird bug followed me at work
Geographic location of the bug: Denison, TX
Time: 09:48 AM EDT
Your letter to the bugman: This bug was on the catwalk and quite aggressive. We also had one come out of the sink inside.
How you want your letter signed: Assassin Bug?
This is a Robber Fly and not an Assassin Bug and those gorgeous green eyes are pretty diagnostic that it is Microstylum morosum, a species also pictured on BugGuide. According to Beetles in the Bush: “Until recently, Microstylum morosum was considered a Texas-endemic. However, Beckemeyer and Carlton (2000) documented this species to be much more broadly distributed in the southern Great Plains (from Texas up into Oklahoma and Kansas and west into New Mexico, Arizona, and Colorado), and Warriner (2004) recorded it shortly afterwards in Arkansas.”
Letter 13 – Robber Fly Question
Subject (please be succinct, descriptive and specific): Robber Flies
Time: 07:46 PM EDT
Your letter to the bugman: A few years ago our property was somehow blessed with the presence of a gang of robber flies. My assumption is they came in on some dead trees that were brought in for milling. They have stuck around for several years now and I would like to make sure they are here for many more. They defend my porch voraciously against the vicious yellow jackets who were the previous residents before the robber flies came. Is there anyway I can insure the survival of the gang? Can I put up nesting sites or winter shelters of some sort? I noticed this year the gang is noticeably smaller after the harsh winter we had. I really don’t want to lose these guys.
Your name: Tareesa
Do you have one or more images of your Robber Flies? If you do, please attach them to our response, but in the future, please use our standard submission form by clicking the ASK WTB? link on our site. That way we would also have your location, an invaluable bit of information for identification purposes. Knowing your exact species of Robber Fly might provide more specific information. We located this family information according to BugGuide: ” larvae usually in soil or decaying wood” and “Minimal courtship behavior. Females lay eggs in the soil or in plants. A few, such as Mallophora and Megaphorus, form an egg mass on a plant stem (photo here). Larvae often predatory, consuming eggs and larvae of other insects in decaying matter. Typically overwinter as pupa, emerge in spring. Life cycle is 1-3 years.” It seems rotting wood is the ideal habitat to encourage their presence. The fact that you have had them for several years is evidence they have what they need, including Yellowjackets for food.
Thank you for the quick reply. I live in northern AZ. I don’t have a picture as these guys are VERY active. It took me forever to ID them and it wasn’t until I witnessed a midair snack session that I was sure of what I had. They are the large black and grey type with the tapered abdomen.Thank you for the additional information and the link. I will be on the look out for the larvae now. I freaking love these guys.
Letter 14 – Robber Fly we believe
Subject: Hornet? Fly? Bee?
Geographic location of the bug: Mount Vernon, Washington state
Time: 12:09 AM EDT
Your letter to the bugman : What IS this? After looking through some images, some characteristics are similar to hover flies, but it was so big! Bigger than a bee or yellow jacket, so I’d guess bigger than hover flies. It’s antennae were so short! It was just in the house near the sliding glass door. In the city but walking distance to rural areas.
How you want your letter signed: Jamie
This is most certainly a Fly and we believe it is a predatory Robber Fly in the family Asilidae. It looks not unlike this Robber Fly from Washington posted to BugGuide. One of the most unique features on your individual is the light orange color on the underside of the abdomen, but this is not a feature that is commonly seen in images posted online.