Cactus Fly: All You Need to Know for a Thriving Desert Garden

In the vast and diverse world of insects, the cactus fly stands out as a particularly intriguing specimen.

Belonging to the Neriidae family, these flies have carved out a niche for themselves in the arid landscapes where cacti dominate.

Their unique appearance and behavior patterns not only make them a subject of interest for entomologists but also for gardeners and plant enthusiasts who encounter them.

This article offers a deep dive into the captivating world of cactus flies, shedding light on their characteristics, lifecycle, and interactions with their primary habitat – the cactus.

Cactus Fly

Longhorn Cactus Fly

What Is a Cactus Fly?

Cactus flies are fascinating insects that belong to the Neriidae family and are known for their unique appearance and interesting behavior.

Let’s take a closer look at their family and the Longhorn Cactus Fly, Odontoloxozus longicornis.

Neriidae Family

The Neriidae family includes about 100 known species of small to medium-sized flies. Some of the main characteristics of this family are:

  • Prominent wings
  • Slender, long-legged
  • Striped bodies
  • Breed in rotting vegetation

One well-known member of the Neriidae family is the Longhorn Cactus Fly, Odontoloxozus longicornis.

Longhorn Cactus Fly Odontoloxozus Longicornis

The Longhorn Cactus Fly, Odontoloxozus longicornis, is a specific type of cactus fly. Its features include:

  • Distinctive long antennae
  • Brown with yellow face.
  • Attracted to cactus plants, especially the flowering parts

Cactus Fly Habitat and Behaviour

Geographic Locations and Plants

Cactus flies are found in desert areas, particularly in the Southwest United States, such as Phoenix, Arizona.

Outside the US, they’re found in Costa Rica. They have also been found in Mexico and south of Cisco, Texas.

They are known to inhabit regions where cacti and other succulent plants thrive due to the growing medium of sand and dry soil.

Some common cacti species that Cactus flies are associated with include:

  • Saguaro cactus
  • Ocotillo
  • Cholla

These plant species vary in size but are all well-suited to the harsh desert conditions.

Banana Stalk Fly

The Desert Lifestyle

Cactus flies are uniquely adapted to their desert environment. Their characteristics include:

  • Ability to withstand high temperatures
  • Efficient reproduction in dry conditions
  • Feeding on nectar from desert plants

Cactus flies serve as pollinators for the saguaro cactus, one of the largest cactus species in the United States, which can grow up to 40 feet tall.

Cactus Fly Lifecycle

The lifecycle of cactus flies, like many other flies, follows a complete metamorphosis, which includes four distinct stages: egg, larva, pupa, and adult.

Here’s a general overview of the lifecycle of cactus flies:

Egg Stage

  • Female cactus flies lay their eggs on suitable substrates, often on decaying cactus or other organic matter.
  • The number of eggs laid can vary, but it’s common for a female to lay hundreds of eggs during her lifespan.
  • The eggs are tiny and may be difficult to see with the naked eye.

Catus Flies Mating

Larva Stage (Maggots)

  • After hatching, the larvae, commonly referred to as maggots, emerge and begin feeding on the decaying cactus or organic matter.
  • The larvae are worm-like in appearance and can vary in color, often being white or cream-colored.
  • This stage is crucial for the fly’s development, as the larvae need to consume enough nutrients to sustain them through their pupal stage.
  • After reaching a certain size and completing their development, the larvae will seek a suitable spot to pupate.

Pupa Stage

  • The larvae transform into pupae, which is a transitional stage between the larva and adult.
  • During this stage, the pupae remain stationary and undergo significant internal changes. They develop the structures and features of the adult fly within the protective pupal casing.
  • The duration of the pupal stage can vary depending on environmental conditions, but it generally lasts several days to a few weeks.

Adult Stage

  • Once development within the pupa is complete, the adult fly emerges.
  • Adult cactus flies are equipped with wings and are capable of flight soon after emerging.
  • They will seek out mates to reproduce and continue the lifecycle.
  • Adult cactus flies feed on various substances, including nectar from flowers.
  • The lifespan of an adult cactus fly can vary, but they typically live for several weeks, during which they focus on reproduction.

Throughout their lifecycle, cactus flies are adapted to thrive in their specific environments, often being associated with cacti and other desert plants.

The exact details of their lifecycle, including duration of each stage and specific behaviors, can vary based on species and environmental conditions.

Water and Moisture Requirements

Cactus flies, like other flies, need water and moisture in their environment. They have adapted to survive in the arid conditions where cacti thrive.

Cacti are known to have unique versions of leaves called spines, which provide shade and collect dew2.

As cactus fly larvae require moisture to develop, the spines’ ability to collect dew and the roots’ ability to absorb water2 create a suitable environment for their growth.

Additionally, the cactus’s pores open at night, which helps keep the overall moisture level in the vicinity3.

File:Telostylinus lineolatus male 2 by kadavoor.jpg

Telostylinus lineolatus male. Source: © 2011 Jee & Rani Nature Photography (License: CC BY-SA 4.0)CC BY-SA 4.0, via Wikimedia Commons

Do Cactus Flies Bite or Sting?

Cactus flies (from the Neriidae family) do not bite or sting humans.

They are primarily herbivores, with their larvae feeding on decaying or diseased cactus tissue.

Adult cactus flies typically feed on nectar or other plant-based substances.

Unlike some other types of flies, cactus flies are not known to be aggressive towards humans or to possess any biting or stinging mechanism.

Do They Carry Diseases?

Cactus flies are not known to transmit diseases to humans.

They are primarily associated with cacti and other plants, with their larvae feeding on decaying or diseased cactus tissue.

While many flies are vectors for diseases, cactus flies are not among those commonly associated with disease transmission to humans or animals.

However, like any insect, they can potentially carry bacteria or other microorganisms on their bodies, but this is not typically a concern in terms of human health.

It’s always a good practice to wash hands after handling any insect or soil to prevent potential contamination.

Damage To Cactus Plants

Cactus flies, specifically their larvae, can cause damage to cactus plants. Here’s how:

  • Larval Feeding: The primary damage caused by cactus flies is during their larval stage. The larvae feed on the tissues of the cactus, particularly on decaying or diseased parts. This feeding can lead to further decay, weakening the plant.
  • Entry Points for Pathogens: The feeding sites can become entry points for bacterial and fungal pathogens. Once these pathogens enter the plant, they can cause diseases or accelerate rot.
  • Stress to the Plant: Continuous feeding and infestation can stress the cactus, making it more susceptible to other pests and diseases.
  • Aesthetic Damage: Apart from the physical harm, the presence of larvae and their feeding activity can mar the appearance of the cactus, making it less appealing, especially for ornamental purposes.
  • Potential for Spread: If an infestation is not addressed, the cactus fly population can increase and spread to other nearby cacti, amplifying the damage.

It’s essential to monitor cacti regularly for signs of infestation and take prompt action if cactus flies or their larvae are detected.

Proper care, including avoiding overwatering and ensuring good drainage, can also help reduce the risk of infestation.

Banana Stalk Fly

Cactus Fly Prevention and Control

Creating a Healthy Garden Environment

To prevent cactus flies, maintain a healthy garden environment. Consider the following:

  • Care for seedlings: Ensure proper care of cactus seedlings in moist soil, especially during winter months.
  • Use coarse sand: Add coarse sand to garden soil to improve drainage and reduce moist conditions favored by cactus flies.
  • Monitor moisture: Avoid over-watering to prevent creating a suitable environment for cactus flies.

Natural and Artificial Control Methods

Several natural and artificial control methods can help manage cactus fly populations:

  • Natural control: Employ carnivorous plants such as sundew or butterwort as natural predators of cactus flies.
  • Gnat traps: Utilize gnat traps to capture adult flies and disrupt their life cycle.
  • Sticky traps: Set up sticky traps coated with petroleum jelly to catch cactus flies without the use of chemicals.
  • Consult a bugman: Seek professional assistance from a bugman if the cactus fly problem persists.

Here’s a comparison table of the control methods mentioned:

Method Pros Cons
Carnivorous plants Chemical-free, natural predators Might not eliminate all flies
Gnat traps Non-toxic, effective Need to be replaced regularly
Sticky traps Chemical-free, low-maintenance Can be unsightly in garden
Professional bugman Expert advice, comprehensive approach Can be expensive, may use chemicals

By implementing these prevention and control methods, you can effectively manage cactus flies in your garden.

Cactus Fly and Houseplant Care

Understanding Cactus Biology

Cactus plants are a type of succulent, which are known for their ability to store water in their leaves or stems.

This adaptation allows them to survive in arid desert environments, as they have evolved to conserve water and nutrients to thrive in these harsh conditions.

Cacti come in various shapes, sizes, and colors, with unique features such as:

  • Stems that can be columnar, spherical, or flattened
  • Spines instead of leaves, which help reduce water loss
  • Areoles, are small cushion-like structures from which spines and flowers grow
  • Flowers that bloom in a wide range of colors, are often pollinated by specialized insect species

Cacti are popular indoor plants in many places, due to their low maintenance requirements and distinctive appearance.

Cactus Fly – Odontoloxozus longicornis

Conclusion

Understanding the biology and behavior of pests like the cactus fly is crucial for effective plant care, especially for those who cherish their cacti gardens.

While cactus flies present certain challenges, with the right knowledge and preventive measures, it’s possible to manage and even prevent infestations.

As with all aspects of gardening, being observant, proactive, and informed is the key to ensuring that your plants remain healthy and vibrant.

Whether you’re a seasoned gardener or a newbie, being aware of potential threats like the cactus fly will equip you to tackle challenges head-on and continue enjoying the beauty and resilience of cacti.

Footnotes

  1. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7457.html 2
  2. https://askdruniverse.wsu.edu/2018/05/10/cacti-survive-hot-dry-environments/ 2
  3. https://www.nps.gov/jotr/learn/nature/cacti.htm

Reader Emails

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 – Banana Stalk Fly from Australia

Subject: What bugs are these?
Location: Cairns, QLD, Australia
December 3, 2016 7:11 am
Found these in my yard.
Signature: CE

Stilt Legged Fly
Stilt Legged Fly

Dear CE,
Like another of your submitted images, we believe this is a Stilt Legged Fly in the family Micropezidae, but unlike the previous image, we have not been successful in finding any matching images from Australia online.  We are postdating this submission to go live to our site when we are out of the office for the holidays at the end of the month.

Correction Courtesy of Karl:  Banana Stalk Fly
Hi Daniel and CE:
This is actually a Banana Stalk Fly (Family Neriidae); we usually call them Cactus Flies in North America. Depending on which source you read, there are either two or three species in Australia. Of these, I believe Telostylinus lineolatus is the closest match. Regards, Karl

Thanks so much Karl.  Interestingly, we have a mating pair of Banana Stalk Flies from Hawaii in our archives, and that posting is also listed as Stilt Legged Flies.  We will create a Cactus Fly subcategory for both postings.

Letter 2 – Mexican Cactus Fly

Large Deep Blue flying insect
October 11, 2009
Bugman,
I saw this gorgeous thing here in Souther California on the first of October this year. It is over an inch long with a heavy body, fast flyer and able to hover easily although it didn’t stay still for very long.
Any Ideas?
Mark Houck
High in Beverly Hills, Los Angeles, California

Mexican Cactus Fly
Mexican Cactus Fly

Hi Mark,
Your photos don’t have the necessary details to make any identification a certainty, however, since we also live in the Los Angeles area and we have seen the Mexican Cactus Fly, Copestylum mexicanum, in our own garden, we are guessing that it is probably the insect you photographed.  The Mexican Cactus Fly is one of the Flower Flies or Hover Flies in the family Syrphidae.  According to Charles Hogue in his book Insects of the Los Angeles Basin:  “This is a giant member of the flower fly family (its body length is 5/8 to 3/4 in, or 15 to 20 mm), with a shiny smooth purplish-black body.”  Hogue also writes:  “the larvae are large … pale cylindrical maggots that feed in the rotting, soupy interior of dead and decaying tissues of cacti.”  You may also see numerous images of stationery specimens posted to BugGuide.

Mexican Cactus Fly
Mexican Cactus Fly

Many thanks. The insect I saw seemed to have a brighter coloring, but everything else looks the same.
Wow- they’re big!
Thanks again.

Mark

Letter 3 – Mexican Cactus Fly

Blue Shiny Bee

Mexican Cactus Fly

Blue Shiny Bee
Location: Torrey Pines, CA
April 11, 2011 10:58 pm
This fat flying bee was hovering around the path and kept coming to the same place – guarding his territory? His large shape reminds me of the Carpenter Bee, but I haven’t been able to identify him. He had a very shiny iridescent blue abdomen. His wings seemed either white or clear with a dark pattern on the forewing and towards the attachment (tegula?) His face was white or at least light. I’ll attach three photos. The first one is best.
Signature: Laura M

Mexican Cactus Fly

Hi Laura,
This is a true Fly, not a Bee.  Most Flies have a single pair of wings while Bees have two pairs.  We do not have time to research the species at the moment, but we will take the time to post all three of your marvelous action photos so that our readership can take a stab at this identification while we are at work today.  The markings on the wings should help in the identification.

We actually followed our suspicions and we believe we are correct that this is a Mexican Cactus Fly, Copestylum mexicanum, a species well represented on BugGuide.

Daniel – thank you so very much! I didn’t know flies could have such large abdomens, or be as large as this was.
Your very speedy answer is very much appreciated!
Laura

Letter 4 – Cactus Fly from Singapore

Subject: Small Insect, Red Eyes
Location: Singapore
February 2, 2013 10:37 pm
Hi there, I found this very minute bug roaming around the rotting stump of a fallen tree. This one is quite lighter in color than the other bugs similar to it. It has those pair of big red eyes. I’m not sure what this is really as it does not seem to be a fly (or could be)? Anyway, hope you guys could identify this one as closely as possible. Oh, sometimes it would wave its two front legs in a movement as if cleaning some sticky debris off its limbs.
Thanks!
Signature: Giovanni

Cactus Fly

Hi Giovanni,
This is in fact a Fly in the family Neriidae which are commonly called Cactus Flies because the “larvae are decomposers of cactus” according to BugGuide.  It might be a Banana Stalk Fly,
Telostylinus lineolatus.  The family is sometimes referred to as Stilt Legged Flies as well, though that name can also refer to the members of the closely related family Micropezidae.  According to the Evolutionary Biology Lab:  “Neriidae is a relatively small family of true flies (Diptera) with long, stilt-like legs. Most species are found in the tropics. Neriids have very interesting behaviours, and many species are strikingly sexually dimorphic, with males having much longer legs, heads and/or antennae than females. Like piophilid flies, neriid larvae have the ability to leap during the stage just before pupation when they migrate from the larval feeding substrate to the pupation site. Very little research has been done on this interesting group of flies.”

Letter 5 – Cactus Joint Bugs

Cactus Bugs
This picture was taken in Carlsbad, New Mexico. Can you identify these cactus bugs?
Thomas Park
Blue Bell, PA

Hi Thomas,
These are Cactus Joint Bugs or Prickly Pear Bugs, Chelinidea tabulata, which is a robust species, varying in color from yellow tho reddish brown, dark olive green or nearly blackish. the length is12 – 15 mm. The nymphs are brownish or dusky with pale green or reddish abdomen. The bugs are nocturnal, often congregating in large numbers on the joints of cactus and causing yellowing, withering, and gradual death of the plants. The species occurs in the arid regions of Texas, New Mexico, Colorado, Arizona, and Southern California. C. vittiger is a similar closely related species.

Letter 6 – Cactus Fly

Subject:  unknown
Geographic location of the bug:  Phoenix, Arizona
Date: 01/28/2018
Time: 09:07 AM EDT
Your letter to the bugman:  maybe 6 or 7 mm long
How you want your letter signed:  Daniel Gronseth

Cactus Fly

Dear Daniel,
This unusual critter is a Cactus Fly in the family Neriidae, probably the Longhorn Cactus Fly,
Odontoloxozus longicornis, which is pictured on BugGuide.  According to BugGuide the habitat is:  “Deserts; larvae in decomposing cacti.”  Thanks to your submission, we have created a Cactus Fly category, moved previously uncategorized postings into the new category, and moved previous postings originally categorized as Stilt Legged Flies into the correct family category.

Letter 7 – Cactus Fly

Subject:  Large black “fly” with clear wings
Geographic location of the bug:  Safari Park Escondido CA
Date: 03/12/2019
Time: 02:58 AM EDT
Your letter to the bugman:  Not sure if this is a rodent bot (?), hope not.
How you want your letter signed:  Linda

Mexican Cactus Fly

Dear Linda,
We love your in flight image of a Mexican Cactus Fly, one of the Hover Flies in the family Syrphidae.  Despite its name, the Mexican Cactus Fly is a native species.  The Mexican Cactus Fly is one of the larger Flies we have seen in our Mount Washington, Los Angeles neighborhood.

Mexican Cactus Fly

Letter 8 – Cactus Fly chilled for photo

Location:  Mt Washington, Los Angeles, California
October 10, 2011
When Daniel arrived at the What’s That Bug? offices after a long day at work, this Mexican Cactus Fly was buzzing loudly at the porch light.  This elusive fly does not like to sit still in the garden, and Daniel has never been successful at getting a photo of a living specimen.  He quickly snatched this one and chilled it for a photo opportunity.  The incandescent lights and ungainly position of the Mexican Cactus Fly don’t really make the most attractive photo, but at least there is a photo to post of this skittish species.  According to BugGuide:  “Larvae feed on rotting cactus. Adults feed on nectar from various flowers.”

Cactus Fly

 

Letter 9 – Cactus Fly, not a Marsh Fly

Summer visitor to chapparal country in Southern California
First of all, I love your website. The variety of life on this planet is more fantastic than any other I’ve visited (at least in recent memory)! My wife and I have long wondered about a winged insect that shows up each year as the weather warms. It seems to like red wine; whenever we go in the backyard with a glass they seem to end up treating our glasses as their personal spa. Since it’s quite dark and looks a bit like the villains in the ‘Babylon 5’ TV series, we call them ‘Shadow Bugs’. They don’t seem harmful; at least they haven’t bitten us yet! We live on the edge of a rocky hill covered in chapparal (cactus, sage, and other desert shrubs). My wife grew up very near here, but in a more urban area and never saw one until we moved to our current house. I would estimate that this critter is between 3/4 of an inch and 1 inch long. In hopes that you can tell us what they are I’m enclosing two pictures. Thanks!
jeff fielding
orange, california

Hi Jeff,
After doing some research, we believe this to be a Marsh Fly in the genus Sepedon. We located some images on BugGuide that look very similar. Perhaps some expert will write in with an exact species.

Correction: Cactus Fly
Provided by Eric Eaton (09/23/2007)
Daniel:
The “marsh fly” is actually a “cactus fly” in the family Neriidae. Fantastic image! We could use it over at Bugguide, as this family is under-represented. Larvae of these insects develop in rotting cacti.
Eric

Correction
(09/23/2007) Maybe a Marsh Fly – not a marsh fly
Hi guys,
I enjoy the site. Your “Maybe a Marsh Fly” from 9/21/2007 is actually a Cactus Fly – Odontoloxozus longicornis. The larvae hang out in decaying cactus. Interesting that the adults like red wine, I’ll forced to experiment with that. Darn. Cheers,
Michael W.

Letter 10 – Mexican Cactus Fly

LARGE Black Fly – Copestylum mexicanum?
Location: Hawthorne, CA
October 23, 2011 7:51 pm
I notice you have some photos of this large, bold fly here at your site. My question is, is mine also a Mexican Cactus Fly? It’s another ”new to the yard” bug, and I didn’t notice that it’s body was blue . . .
Signature: Thanks, Anna Carreon

Mexican Cactus Fly

Hi Anna,
Your identification of the Mexican Cactus Fly is correct.  The body is actually black with a blue sheen.  The blue sheen only shows when the light strikes the fly’s body from the right angle.

Mexican Cactus Fly

Thanks Daniel!  I noticed that in a related post you say that this is a skittish fly.  For some reason, our yard seemed to calm this particular specimen.  It stayed for long periods of time and didn’t seem to mind the camera being very close to it.  Not the first skittish bug this has happened with.  We wonder why this is.
Anna

Letter 11 – Mexican Cactus Fly

Subject: large shiny black fly
Location: Walnut Creek, CA
December 22, 2014 10:42 pm
This fly is larger than a large housefly and is conspicuously hairless compared to a housefly. It is jet black and has interesting colored patches on its wings.
Signature: Dirk

Mexican Cactus Fly
Mexican Cactus Fly

Dear Dirk,
This is a wonderful image of an impressive fly in the family Syrphidae, commonly called a Mexican Cactus Fly,
Copestylum mexicanum.  According to BugGuide:  “Larvae feed on rotting cactus” and adults are frequently seen visiting flowers. 

Thank you, Daniel!  It somehow makes a big difference to the enjoyment of an image to know who the subject is.  Dirk

Letter 12 – Mexican Cactus Fly

Subject:  bee fly
Geographic location of the bug:  San Diego, California
Date: 11/04/2017
Time: 03:56 PM EDT
Size of a medium bumblebee. There were a dozen working the flowers in the photo.
How you want your letter signed:  Gerald Friesen

Mexican Cactus Fly

Dear Gerald,
This is not a Bee Fly.  It is a Mexican Cactus Fly, a species of Flower Fly or Hover Fly in the family Syrphidae.  According to BugGuide:  “Larvae feed on rotting cactus.”

Mexican Cactus Fly

Letter 13 – Mexican Cactus Fly

Subject:  Mexican Cactus Fly?
Geographic location of the bug:  Tucson, Arizona
Date: 12/30/2019
Time: 03:29 PM EDT
Your letter to the bugman:  I photographed these flies as they visited flowers at the Tucson Botanical Gardens in Tucson, Arizona.  I think that they may be Mexican Cactus Flies; and I was hoping that you could confirm that.  Of course, you may use the photos if so desired.
How you want your letter signed:  Stephen Nelson

Mexican Cactus Fly

Dear Stephen,
This is indeed a Mexican Cactus Fly,
Copestylum mexicanum.  Though the Mexican Cactus Fly is a member of the Hover Fly family Syrphidae, it does not resemble most other members of the family that look like bees and wasps as protective mimicry.

Letter 14 – Mexican Cactus Fly in Elyria Canyon Park

Mexican Cactus Fly
Location:  Elyria Canyon Park, Los Angeles, California
April 14, 2012
After participating in a bird watching hike, Daniel headed home on the path that passes along “dirt” Burnell where four additional lots have recently been purchased and added to the total acerage for the Elyria Canyon Park.  The wild mustard was blooming and this large Mexican Cactus Fly, , did not seem at all concerned that it was being photographed.  Perhaps because the weather was so cool, this member of the Hover Fly family Syrphidae was not as wary as it might normally be. 

Mexican Cactus Fly

According to Charles Hogue in Insects of the Los Angeles Basin: “This is a giant member of the flower fly family (its body length is 5/8 to 3/4 in. or 15 to 20 mm), with a shiny smooth purplish-black body’  it is occasionally seen in the spring and summer in areas where cacti grow.  The larvae are large (body length 3/4 in. or 20 mm) pale cylindrical maggots that feed in the rotting, soupy interior of dead and decaying tissues of cacti.”

Mexican Cactus Fly

 

Letter 15 – Cactus Fly from Philippines

Weird fly from the Philippines (2)
December 27, 2009
Dear Bugman,
What’s this bug?
I saw this guy on the outer wall of our house. At first I though it was some kind of assassin bug, but then I realized it must be some strange kind of fly! I had never seen its kind before.
Could you let me know what it is?… Thanks!
Kulisap
Luzon, Philippines

Unknown Fly
Cactus Fly

Dear Kulisap,
We do not recognize this fly and we will post its image in the hopes that one of our readers may be able to provide a response.  If you post a comment to the posting, you will be informed automatically if someone writes to us in the distant future.  Your photos are quite good, and we hope we get a proper identification, at least to the family level.

Unknown Fly
Cactus Fly

Update:  December 30, 2009
After some searching I think I was able to identify this critter… it seems to be a type of cactus fly (Neriidae).
I also found this link:
http://www.bonduriansky.net/neriidae.htm
Thanks again for the reply!
Kulisap

Letter 16 – Mating Banana Stalk Flies from Hawaii

Special Mosquitos?
Location: Palolo Valley, Honolulu, HI
December 16, 2010 5:39 pm
Found these two getting busy on the shoe rack this morning… I hope they don’t recognize and remember faces for an attack later on when they’re done… Are these special mosquitoes or something? They sure don’t look like a regular Mosquito!
Signature: TH

Mating Banana Stalk Flies

Dear TH,
Wow, what an awesome photo you have sent to us.  We have no idea where to begin researching the identity of these unusual looking mating Flies, but we can assure you that they are not mosquitoes.  Like so many other creatures in Hawaii, we suspect these might be an introduced species, possibly from Asia.

Immediate Update
We quickly found a match for your mating Flies.  They are identified on BugGuide as Banana Stalk Flies, Telostylinus lineolatus, in the family Neriidae, the Stilt Legged FliesThe Cook Islands Biodiversity website has a page devoted to the Banana Stalk Fly, and they list the other common names Banana Fly, Push-me-Pull-me Fly and Push-pull Fly.  The range is listed as “Sri Lanka – Indonesia / Australia – Marquesas, Hawai‘i” and it is considered a pest species, but the site does not indicate why.  The Rainforest Revelations website has this information:  “With enormous eyes, this tiny, tropical, stilt-legged fly maintains a confident distance from human approach, by swiftly running around the blind-side of whatever surface it is on.  … Telostylinus lineolatus inhabits tropical north Queensland, where it aggregates on flowers and rotting fruit.  They are members of Neriidae, which is a relatively small family of true flies (Diptera) with long, stilt-like legs.”  The Evolutionary Biology Lab Research website has this information on the family:  “Neriidae is a relatively small family of true flies (Diptera) with long, stilt-like legs. Most species are found in the tropics. Neriids have very interesting behaviours, and many species are strikingly sexually dimorphic, with males having much longer legs, heads and/or antennae than females. Like piophilid flies, neriid larvae have the ability to leap during the stage just before pupation when they migrate from the larval feeding substrate to the pupation site. Very little research has been done on this interesting group of flies.

Correction January 2, 2017
Though we correctly identified the species, we now know that Banana Stalk Flies are in the Cactus Fly family Neriidae.

Authors

    by
  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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