Fishfly vs Mayfly: Unveiling Key Differences in Aquatic Insects

Fishflies and mayflies may appear similar to the untrained eye, but in reality, these are two distinct types of insects belonging to different families. While both are aquatic insects and play essential roles in the ecosystem, understanding their differences can help us appreciate the diversity of the insect world and their contributions to the environment.

Fishflies belong to the family Corydalidae, which consists mainly of dobsonflies. These insects dwell in various aquatic habitats, ranging from streams and rivers to still ponds and even tree holes, depending on the species (source). On the other hand, mayflies are part of the order Ephemeroptera and are unique among insects due to their distinct subimago stage in their life cycles (source).

This article will discuss the key differences between fishflies and mayflies, including their morphology, behavior, and their roles in ecosystems. By recognizing these differences, we can better understand the unique characteristics of each insect and the important functions they serve within their habitats.

Fishfly and Mayfly Overview

Taxonomy and Scientific Names

Fishflies and mayflies are two distinct groups of insects. Mayflies belong to the order Ephemeroptera while fishflies belong to the family Corydalidae.

Distribution and Habitat

• Mayflies are found across:

  • North America
  • Central America
  • South America
  • Eurasia
  • Africa
  • South Africa
  • Madagascar
  • Oceania
  • Australia
  • Asia

• Fishflies are distributed in:

  • North America
  • Central America
  • South America
  • Asia

Appearance and Morphology

Mayflies and fishflies differ significantly in their appearance and morphology.

Mayfly:

• Slender body

• Two pairs of triangular wings

• Short antenna

• Two or three threadlike tails

Fishfly:

• Round wings

• Feathery antennas

• Fragile

In conclusion, fishflies and mayflies are two different insect groups, belonging to different scientific families. They are found in various parts of the world and have different appearances, with mayflies having a slender body, triangular wings, and short antennas, while fishflies have round wings and feathery antennas.

Life Cycle and Behavior

Larval Stage and Naiads

Mayflies and fishflies both have aquatic larvae stages. Mayfly larvae, also known as naiads, live in various aquatic habitats, feeding on algae and organic matter. Fishfly larvae are similar in appearance but have key differences, like mouthparts.

Some features of mayfly naiads include:

• Gills for breathing underwater
• Buggy-looking eyes
• Ranging from one centimeter to several centimeters in length

Adult Stage and Mating

The adult stage for both insects is short-lived. Adult mayflies have a unique sub-adult stage called the subimago before developing into their winged adult form, also known as the imago stage. Adult mayflies have slender bodies, large compound eyes, and four membranous wings held upright together source.

During the adult stage, mayflies focus on mating, with male mayflies using their large compound eyes to locate females. Adult fishflies, on the other hand, do not have a subimago stage and go straight from larvae to winged adults.

A comparison of mayflies and fishflies in the adult stage:

Swarming and Blooms

Swarming behavior can be observed in both mayflies and fishflies. Swarms are large populations of flying insects that gather in one area for mating purposes. Both insects exhibit swarming behavior due to their short adult lifespan of just a few days.

Water quality plays a significant role in mayfly blooms, as better water quality supports larger mayfly populations. When large numbers of mayflies emerge from their larval stage to swarm, it is called a bloom. These blooms are a sign of healthy aquatic ecosystems within the Order Ephemeroptera.

Physical Differences

Wings and Tails

Fishflies and mayflies share some similarities, but they differ mainly in their wings and tails. Both adult mayflies and dragonflies have two pairs of wings, but mayflies have larger, triangular front wings and smaller, round hind wings¹. On the other hand, adult fishflies, like dobsonflies, have two pairs of equal-sized wings². Mayflies also have long tails with two or three filaments³, while dragonflies and fishflies have short cerci⁴.

Mayflies:

• Two pairs of wings (triangular front wings and smaller, round hind wings) ⁵
• Two or three long tail filaments ⁶

Fishflies:

• Two equal-sized pairs of wings ⁷
• Short cerci ⁸

Gills and Abdomen

Mayfly nymphs possess gills along their abdomens, which help them respire underwater ⁹. Fishflies also have gills, but they are found on the thorax of their larvae¹⁰. The adult stages of both insects do not have gills. Another difference is mayflies tend to have delicate, elongated bodies, while fishflies have more robust bodies.

Mayflies:

• Gills on abdomen (nymphs only) ¹¹
• Delicate, elongated bodies ¹²

Fishflies:

• Gills on thorax (larvae only) ¹³
• Robust bodies ¹⁴

Eyes and Antennas

Both mayflies and fishflies exhibit differences in their eyes and antennas. Adult male mayflies have large, compound eyes that facilitate mate searching¹⁵, while adult female mayflies have smaller eyes¹⁶. In contrast, fishflies, like dobsonflies, have smaller, more evenly sized eyes¹⁷. Furthermore, mayflies have short, bristle-like antennas¹⁸, while fishflies have longer, more conspicuous antennas¹⁹.

Mayflies:

• Large, compound eyes (male) ²⁰
• Short, bristle-like antennas ²¹

Fishflies:

• Smaller, evenly sized eyes ²²
• Longer, conspicuous antennas ²³

Ecological Role and Impact

Aquatic Insects and Water Quality

Mayflies and fishflies, both aquatic insects, significantly contribute to water quality. They serve as indicator species, with their presence representing healthy freshwater ecosystems. These insects play a crucial role in the following processes:

• Breaking down organic matter
• Recycling nutrients within aquatic environments
• Maintaining balanced water ecosystems

Feeding Habits and Impact on Ecosystem

Mayflies:

• Primarily feed on algae, dead leaves, and living plants in their nymph phase
• Directly affect the freshwater ecosystem by controlling algal populations
• Contributes to nutrient cycling and food chains

Fishflies:

• Also known as chauliodes rastricornis
• Carnivorous, preying on smaller aquatic insects
• Contributes to the natural balance by maintaining insect populations and nutrient cycling

The different feeding habits of mayflies and fishflies help establish a harmonious food chain and nutrient balance within aquatic ecosystems.

Fishflies and Mayflies as Prey

Both mayflies and fishflies serve as crucial prey for a variety of freshwater vertebrates, particularly fish. Notable examples include trout, which consume mayfly nymphs in a feeding strategy known as the “drift.” Additionally, anglers imitate mayflies as bait, known as “shadflies” or “up-winged flies.”

A comparison of fishflies and mayflies can be summarized in the table below:

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 – Fishfly

night flying insect
Hi,
This is a night flying insect i see every year at this time . i love to watch them fly around my porch at night. There wings are like fairies in flight . I call them the fairy bug . There so cool. can you please tell me what it is? thank you so much…
celine m devlin

Hi Celine,
This is a Fishfly in the genus Chauliodes. It is in the same family as Dobsonflies. Fishflies are often attractred to lights at night and are found near bodies of water.

Letter 2 – Fishfly

Subject:  Lacewing?? Not sure
Geographic location of the bug:  Puslinch, Ontario, canada
Date: 07/10/2020
Time: 11:50 PM EDT:  We don’t often see really large bugs in our area. And I’ve never seen this bug before around our property. It was just sitting on the side of our gazebo in the sun for hours and hours. I thought it might be a lacewing of sorts but it’s antennae don’t look right as this guy has the feathered type rather than the clubbed.
How you want your letter signed:  Karen Gray

Dear Karen,
This is a Fishfly in the genus Chauliodes.  Its feathered antennae distinguish it from its larger relative, a Dobsonfly.

Letter 3 – Female Spring Fishfly

Subject: What is this?
Location: North Texas area close to Dallas Lake Ray Hubbard
April 21, 2014 11:14 am
Found this bug on the front of my house under the garage light. Has been there for 3 or 4 days now and has only moved a couple of inches that I know of. You can estimate it’s size from the standard house brick it is sitting on. Did not want to bother it until I knew what it was or may be doing. Thank you for your help in the past and I hope you had a great Easter.
Signature: Dan in Texas

Dear Dan,
This sure looks like a female Spring Fishfly, Chauliodes rastricornis, to us.  According to BugGuide:  “The antennae of females are almost linear, with just a little jagginess on the edges, i.e., serrate (saw-like)” and “Adults typically fly late spring: March?-May (North Carolina), April-May (West Virginia). Seen into early June in New England (Massachusetts–guide photo). Further south, much of year (Florida).”

Letter 4 – Female Spring Fishfly

Subject: ?bug
Location: Logansport, Indiana
May 18, 2015 5:58 pm
This is on a piece of wood. Wings are about 2 inches long. Never seen one before?
Signature: Bonnie Brown

Hi Bonnie,
We suspect you live near a body of water.  This is a female Spring Fishfly, Chauliodes rastricornis, and according to BugGuide:  “The antennae of females are serrate (saw-like).  The comb-like, (pectinate) antennae of the males are quite obvious.”  You many compare your individual to this image posted to BugGuide.

Letter 5 – Female Summer Fishfly

Subject: Strange fly in resort
Location: Florida
August 1, 2016 6:24 am
We are in Orlando, Fl and we found this bug in our resort and my son is very interested in creepy crawlies much to my dismay and he would like to know what it is!
Signature: Doesn’t matter

Dear Doesn’t matter,
By comparing your image to this BugGuide image, you can see you have submitted an image of a Summer Fishfly, Chauliodes pectinicornis. 

Letter 6 – Fish Fly

Subject: Please tell me what this bug is please!
Location: Kathleen, Florida
January 10, 2013 9:27 am
This is the first time we have seen this bug and do not know if we need to do anything about it. We live on a farm and have animals. Thank you!
Signature: Sincerely, Denise

Hi Denise,
Though your photo is blurry, it appears by the antennae that this is a Fishfly in the genus Chauliodes.  You can see BugGuide for additional information.

Dear Daniel, I can’t thank you enough for getting back with me!!! Please except my deepest thanks!! I am very greatful! Denise

Letter 7 – Fish Fly

Subject: large, winged insect
Location: Sylacauga, Alabama
June 5, 2015 5:26 am
Found on my screen and when i caught in a bucket, it flew to a nearby tree.
Signature: JMBama

Dear JMBama,
This is a Fishfly in the genus Chauliodes, and we believe because of the BugGuide description of the Spring Fishfly, Chauliodes rastricornis: “Compare C. pectinicornis. Head and pronotum have dark markings on light brown background, as opposed to yellowish markings on dark brown background of C. pectinicornis” that you have a Summer Fishfly as your individual has yellow markings on the pronotum behind the head.  We are postdating your submission to go live in the future while we are away from the office for a spell in mid-June.

Letter 8 – Fishfly

Fish fly?
Dear Bugman,
From the pictures in you site I believe this is a Fish Fly. I found it in my living room watching the soccer game. Since it seemed very comfortable and was not moving much I decided to take the time to take some close-ups. Found in Lexington, MA
Regards,
Jaime

Hi There Jaime,
Dobsonflies and Fishflies both belong to the order Megaloptera along with Alderflies. Further classification puts the Dobsonflies and Fishflies in the Family Corydalidae and Fishflies are in the genus Chauliodes. This is a Fishfly

Letter 9 – Fishfly

Female Dobsonfly?
What an awesome website you have! We live in Des Moines, Iowa, less than 1 mile from the Des Moines River. Today we were out working in the yard and when I went to sit in my lawn chair, I discovered this creature had landed on it! We did a quick catch-and-release so we could get a good photo, and I thought you might like the shot of her from the front. We’re pretty sure… after Googling the string, bug wings pinchers, and finding your site… that it’s a female dobsonfly. Can you confirm? I have to say it’s probably the ugliest thing I’ve ever seen… but, fascinating nonetheless! Thanks for a fun and informative site!
Janet Green, Des Moines Iowa

Hi Janet,
We expect to be getting plenty of photos of Dobsonflies in the coming months. Eric Eaton has this to say about this specimen: “The female dobsonfly is likely a different kind of Fish Fly. Please see bugguide for the alternatives (Chauliodes sp??).”

Letter 10 – Fishfly

Bug
I was wondering if you could help me identify this flying bug..thanks
Jeff Zuidema

Hi Jeff,
This is a Fishfly which is closely related to Dobsonflies. Fishflies are smaller and have antennae feathered on one side.

Letter 11 – Fishfly

What is it?
Hi Bugman,
I snapped these pictures this morning (Mt. Laurel, NJ). Never saw this one before, and have no idea what it is. Thanks,
Tim

hi Tim,
We fired a quick incorrect response to you that this was a Dobsonfly, when in fact it is a Fishfly. Fishflies have comblike antennae that distinguish them from Dobsonflies that have beaded antennae.

Letter 12 – Fishfly

hi this bug is about 2 or 3 inches long i have know clue what it is hopefully you can help. i seen it at our camp site in Oakham Mass. thank you
cheryl

Hi Cheryl,
This is a Fishfly, and we are guessing it wasn’t seen this week.

Letter 13 – Fishfly

Unidentified critter
Hi,
I was just introduced to your great site by my son: until now he has been my resource for these things, based on one course back in high school. I have been getting into macrophotography over the past year, and have become amazed at the diversity of insects and spiders the right here in suburban Boston area. At my son’s suggestion, I have started using a blacklight to bring out more in the evening. This fellow had a body length of 1.5 to 2 inches (4-5 cm), was a weak flyer, just sort of fluttering around. … Thanks for any help!
Mike

Hi Mike,
This is a Fishfly. Fishflies from the genus Chauliodes can be distinguised from their close relatives, the Dobsonflies, because Fishflies have feathered antennae. BugGuide has much information on Fishflies.

Letter 14 – Fishfly

help identifying an insect
Location: Owen Sound, Ontario
July 18, 2011 1:27 am
I think this is a Dobsonfly but I’m not entirely sure i found it around 1AM on a warm summer night
Signature: kyle

Hi Kyle,
Dobsonflies are in the insect order Megaloptera which also contains Fishflies and Alderflies.  This is a Fishfly.  They can be distinguished from Dobsonflies by their antennae.

Letter 15 – Fishfly

Subject: Unknown morning visitor
Location: Rhode Island
May 28, 2014 4:19 am
This bug was outside my front door on the house this morning. Any ideas what it is?
Signature: Robin G

Dear Robin,
This is a Fishfly in the genus Chauliodes, and because of the pectinate antennae, it is a male.  Because of the season, we strongly suspect this is a Spring Fishfly, Chauliodes rastricornis, and you can learn more about it by visiting BugGuide.

Letter 16 – Fishfly

Subject:  Winged bug
Geographic location of the bug:  Woodbury CT
Date: 09/20/2017
Time: 09:32 PM EDT
Can you please tell us what this bug is? It was out at night by our front porch light.
How you want your letter signed:  Nancy

Dear Nancy,
This is a Fishfly, and considering the season, we speculate it is a Summer Fishfly, Chauliodes pectinicornis. According to BugGuide:  “Antennae pectinate in both sexes”

Letter 17 – Fishfly

Subject:  Large winged insect
Geographic location of the bug:  Western Pennsylvania
Date: 05/27/2019
Time: 07:22 PM EDT
Your letter to the bugman:  Found this very weak insect on our back porch today. Never saw its kind around here and was wondering if you folks would know its species.
How you want your letter signed:  Richard

Dear Richard,
This is a Fishfly in the genus Chauliodes.  According to BugGuide:  ” Larvae leave the water to pupate under bark or in rotting wood; pupal period takes ~10 days. Adults live a week or less. Eggs are laid in masses on vegetation near water. Larvae hatch and crawl to water.”

Letter 18 – Fishfly

Subject:  Not sure
Geographic location of the bug:  Teeswater Ontario
Date: 07/24/2019
Time: 07:35 PM EDT
Your letter to the bugman:  This bug was flying around the back yard and night. Dont know what it is can you help
How you want your letter signed:  Miss marci

Dear Miss Marci,
This is a Fishfly in the genus Chauliodes, and because the antennae in your individual appear to be serrate, we are concluding that this is a female Spring Fishfly, which is pictured on BugGuide.  Despite being called a Spring Fishfly, there are Ontario sightings as late as September according to BugGuide data.

Letter 19 – Fishfly Identification

Your website
Just wanted to pass along I identified a bug I’ve never seen before I found in my driveway (a fishfly). You’re site is much more helpful than the load of University web sites and bug-o-pedias I searched before stumbling across Whatsthatbug.com. I’ve spent the last hour just browsing and learned alot. I’m certain I will be back when my 4-yr old brings me another bug he’s stumbled across. Thanks. Kelly Wagoner
Woodstock, GA

Hi Kelly,
Thanks for the compliment. Since we are not associated with an institute of higher learning, we can afford to be a bit quirky.

Letter 20 – Fishfly Larva in the snow in Washington

Subject:  What is this?
Geographic location of the bug:  West slope of the Cascades, Washington.  Ele 2000 ft
Date: 03/25/2018
Time: 01:35 PM EDT
Your letter to the bugman:  Saw this walking on the snow.  Some kind of wood eater?  There is natural hot springs in the area.
How you want your letter signed:  Dylan Rhys

Dear Dylan,
Because the critter in your image looks so similar to a Hellgrammite, we are concluding that it is a nymph in the same family, and that it is most likely the nymph of a Fishfly.  Unfortunately, there is not much visual documentation of the larvae of western species.  What excites us most about your submission is that we can tag your posting as a Snow Bug.