Fungus Gnats vs Fruit Flies: Key Differences and Control Methods

Fungus gnats and fruit flies are two common pests that can be found in our homes, especially around potted plants and fruits. Both insects can be a nuisance, but they have distinct characteristics that set them apart.

Fungus gnats are delicate, dark brown or black flies that are about 1/8 inch long, with larvae resembling pale worms and having a black head. They usually infest soil, potting mix, and other sources of organic decomposition. Their larvae primarily feed on fungi and organic matter in soil, while occasionally chewing on roots, making them a problem in greenhouses, nurseries, and potted plants.

On the other hand, fruit flies are typically smaller and more robust, resembling tiny houseflies, with a preference for ripe and fermenting fruits. They can easily be identified by their red eyes and rapid reproduction rates. These flies pose a threat to fruit safety in homes and stores, as they can transmit bacteria and cause spoilage.

Fungus Gnats vs Fruit Flies: Understanding the Difference

Appearance

Fungus Gnats

• Delicate, mosquito-like insects
• Long legs and antennae
• Distinct “Y-shaped” pattern on forewings ¹

Fruit Flies

• Rounder, more robust body shape
• Shorter legs and antennae
• No distinct wing pattern

Size and Color

Habitat and Food Source

Fungus Gnats

• Prefer moist environments
• Often found in greenhouses, homes, and offices²
• Larvae feed on fungi, decaying organic matter, and plant roots⁴

Fruit Flies

• Attracted to overripe or fermenting fruits and vegetables
• Common in kitchens and other areas where food is stored
• Adults feed on sugars, while larvae feed on decaying organic material

Breeding and Life Cycle

Fungus Gnats

• Lay eggs on the surface of the plant soil⁴
• Eggs hatch after approximately 3 days⁴
• Larval stage lasts about 10-14 days¹
• Adults live for about 7-10 days²

Fruit Flies

• Lay eggs on or near fermenting food
• Eggs hatch within 24-30 hours³
• Larval stage lasts about 4-5 days³
• Adults live for about 10-20 days³

In summary, while both fungus gnats and fruit flies are small flying insects, they differ in appearance, habitat, and lifecycle. Recognizing these differences can help you identify and manage these pests effectively.

Identification and Common Confusions

Eyes

Fungus gnats and fruit flies can be distinguished by their eyes. Fungus gnats have small, beady eyes while fruit flies have larger, reddish eyes.

Example:

• Fungus gnats: small, beady eyes
• Fruit flies: large, reddish eyes

Wings and Antennae

Another key difference between these two pests are their wings and antennae. Fungus gnats have a distinct curved “Y” fork in their wings, while fruit flies have plain wings. As for antennae, fungus gnats have longer, segmented ones, while fruit flies have short, stubby antennae.

Comparison Table:

Damage and Nuisance Caused

While fungus gnats and fruit flies are both common indoor pests, they cause different kinds of damage and nuisance.

Fungus gnats:

• Mainly feed on the roots of houseplants, causing damage to the plants.
• Adult gnats are weak fliers, often found resting on plant soil or foliage.
• They are mostly nuisance pests, causing little harm to humans.

Fruit flies:

• Attracted to rotting fruit and vegetables, can contaminate food.
• They breed quickly, making them tough to control once an infestation starts.
• Fruit flies can transmit diseases to humans through contaminated food.

Due to these differences, it is important to accurately identify the type of pest in order to apply the most effective control methods.

Prevention and Control Strategies

Watering and Soil Management

Proper watering and soil management can help prevent fungus gnats and fruit flies. Fungus gnats thrive in damp, organic matter-rich soil.

• Allow the top layer of soil to dry before watering.
• Reduce the amount of organic matter in the soil mix.
• Employ well-draining soil to avoid excess moisture.

Methods for Getting Rid of Gnats

There are various methods to control and eliminate fungus gnats and fruit flies.

• Use yellow sticky traps to catch adult gnats.
• Apply Bacillus thuringiensis israelensis (Bti) or Steinernema feltiae nematodes to soil to target larvae.
• Consider chemical control with pyrethrins or pyrethroids only when other methods fail.

Comparison Table:

Encouraging Natural Predators

Attracting natural predators can help control these pests.

• For fungus gnats, introduce predatory mites or predatory rove beetles like Atheta coriaria.
• Utilize insects like parasitic wasps to target fruit flies.

Remember, prevention techniques are key to avoiding infestations of both fungus gnats and fruit flies.

Home Remedies and DIY Traps

Vinegar and Dish Soap Traps

Vinegar and dish soap traps are a popular method for combating both fungus gnats and fruit flies in the home. One common recipe involves mixing equal parts of water and apple cider vinegar in a container, then adding a few drops of dish soap. The vinegar attracts the gnats and fruit flies, while the dish soap makes them unable to escape, causing them to drown.

Pros:

• Inexpensive
• Easy to create
• Uses common household items

Cons:

• May require multiple traps
• Needs regular replacement of mixtures

Boiling Water and Baking Soda

Boiling water and baking soda can help control fungus gnat and fruit fly populations by targeting their larvae in drains, where they often reproduce. Pour boiling water down your drains to kill any eggs or larvae in the pipes. A combination of baking soda and white vinegar will also break down any dirt or organic matter that could serve as a breeding ground.

Pros:

• Targets larvae and eggs
• Cleans drains

Cons:

• May not be effective against adult insects

Creating Fruit and Wine Traps

Fruit and wine traps are another home remedy that targets both fungus gnats and fruit flies. Half-fill a container with your choice of bait – such as red wine, pieces of ripe fruit, or fruit juice. Cover the container with a perforated plastic wrap, allowing the insects to enter but making it difficult for them to escape.

Pros:

• Attracts a range of insects
• Can be sealed for easy disposal
• Can use a variety of baits

Cons:

• Bait may spoil, requiring replacement

Comparison of Methods

Professional Solutions and Products

Insecticides and Pest Control Services

• Terro: Terro offers an effective liquid fruit fly trap that lures fruit flies into a non-toxic liquid solution, trapping and killing them.

  Pros: Easy to use, non-toxic for humans and pets
  Cons: Suitable for fruit flies but not designed for fungus gnats

• Orkin: Orkin is a well-known pest control service that can help homeowners get rid of both fungus gnats and fruit flies with tailored treatment plans.

  Pros: Professional service, customized treatment plans
  Cons: Costlier than DIY solutions

Potting Soil and Drain Treatments

• Bacillus thuringiensis var. israelensis (Bti): Bti-containing products can be applied as a soil drench or granules for fungus gnat control.

  Pros: Effective for controlling fungus gnat larvae, safe for humans and pets
  Cons: Not effective against fruit flies

• Hydrogen peroxide: A 1:4 solution of 3% hydrogen peroxide and water helps control fungus gnats by killing larvae present in the soil without harming your plants.

  Pros: Affordable and easy to use, non-toxic
  Cons: Not suitable for fruit flies

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 – Crawling Mass of Fungus Gnat Larvae

Subject: What the hell are these
Location: NWA
June 21, 2014 8:53 am
Hey Bugman,
Yesterday morning I came across 5 groups of these slugs (I believe that’s what they are). I live in North West Arkansas. So far I haven’t been able to find anything on web about what these little guys actually are. Most people are telling me that they are tent caterpillars, but I don’t believe that is correct.
Signature: J. Ramey

Dear J Ramey,
This is a crawling mass of Fungus Gnat Larvae in the family Sciaridae.  According to the Home, Yard & Garden Newsletter at the University of Illinois:  “Fungus gnat larvae are more likely to be numerous in areas with an overabundance of water from rainfall or irrigation. Over-watering newly laid sod can result in large populations of these larvae eating young roots. Reducing irrigation will cause a reduction in the number of fungus gnat larvae and allow the sod to root.  These larvae are not likely to cause any damage to established turf and can be ignored or washed away with heavy streams of water. As adults, they are known as dark-winged fungus gnats, which are frequently very common in the spring and fall in Illinois, flying as large swarms up to several feet across.”  

Letter 2 – Aggregation of Fungus Gnat Larvae

Subject: need help with ID of worm masses
Location: North Carolina
July 7, 2012 3:43 pm
Hi,
Can you help ID this mass of Asheville, North Carolina worms sent to me to ID (no luck)? Several masses of worms were found on concrete on their property.
Signature: John

Dear John,
This is an aggregation of Fungus Gnat Larvae.  Here is some information from the University of Delaware Cooperative Education website:  “As a result of our unusually wet weather, I’ve been receiving some interesting inquiries and digital images from arborists, landscapers, and homeowners. Their questions or observations are usually described to me as if they’re seeing ‘worms’, ‘tapeworms’, ‘processionary caterpillars’, or ‘armyworms’ crawling across the landscape, sidewalk or driveway. The masses are slimy or wet looking and several inches to several feet long as they move over landscape timbers and other surfaces. Even though this behavior is not yet understood entomologically, past experiences have allowed me to accurately identify these masses of larvae as an aggregation of darkwinged fungus gnat larvae. Observations of these masses of larvae are usually associated with a rich organic soil environment such as a recently mulched area where turfgrass is being established or shady, damp regions of the landscape. The larval stage of a darkwinged fungus gnat is thin, white, and legless with a shiny black head capsule. They have a smooth, somewhat transparent exoskeleton that reveals digestive tract in the center of the abdomen. Mature larvae are about 3 mm (1/8 inch) long. When
hundreds of these larvae congregate together to form a ribbon-like mass it is indeed an unusual sight in a landscape. Darkwinged fungus gnat larvae feed on the roots of many different plants and organic matter in the United States. They are recognized as important pests in greenhouses and mushroom cellars. They are also pests of houseplants. Adults and larvae inhabit moist, shady areas. Adults are very small, sooty gray or nearly black, long-legged, slender flies that live about 1 week. Females deposit 100-300 eggs on soil, usually near the base of plants. Larvae reach maturity in about two weeks and then construct a pupal case in soil. There is no reason to treat these masses of darkwinged fungus gnat larvae. Use this unusual insect behavior as an opportunity to educate your clients regarding the diversity and importance of insects in their landscapes.”

Daniel, thanks so much!  This is my second request over the years and I continue to be impressed with your skills and your website.
I just made a $10 donation to support your website; … .
All the best!  -John
PS: I’m looking forward to sharing the fungus gnat info with my NC friend when I see her soon.

Letter 3 – Aggregation of Fungus Gnat Larvae

Maggots of some sort
Location: Hamlin, NY about 5 miles south of the Lake Ontario shore
November 7, 2011 11:03 pm
Hi. I found these pods of worms or maggots in the gutter on the side of the road in front of our house one early morning on September 15, 2004. We are in Hamlin, NY about 5 miles south of the Lake Ontario shore. These pods of worms moved together like a single unit. Notice there are two kinds of worms in the pods. The majority of the worms are about 1/32” in diameter. The larger maggots, there was one or two in a pod, looked like a typical large green bottle fly maggot. I have not seen anything like this before or since then. I have shown these pictures to a lot of people and no one even has a guess as to what these might be.
Signature: What’s that bug?

This curious phenomenon is an aggregation of Fungus Gnat Larvae in the family Sciaridae.  Here is a photo from BugGuidewith some information.  We don’t believe there are two species here, rather we suspect that some of the individuals in the aggregation are larger.

Letter 4 – Aggregation of Fungus Gnat Larvae

What are these?
May 28, 2009
Found two clumps of hundreds of these creatures outside on my patio, all moving together in the same general direction. They’re slimy, slippery…almost slug-like, but appear to be larvae of some sort.
Eric
Charlotte, North Carolina

Hi Eric,
We apologize for the lengthy delay.  We are trying to respond to some of our long overdue unanswered requests.  These are Fungus Gnat Larvae.  The Hydro Gardens website has some information.  You can also see a matching photo from Alaska on the Social Caterpillar website of Cortland faculty.  BugGuide also has a posting discussing the aggregations of the larvae of Dark Winged Fungus Gnats in the family Sciaridae.

Letter 5 – Aggregation of Fungus Gnat Larvae

Subject: swarm of caterpillars
Location: Fairfax, VA
July 21, 2015 11:40 am
This has got to be the most unusual behavior I’ve ever seen – a swarm of small (5 – 8 mm in length), translucent caterpillars, slowly moving across a sidewalk (to get to the other side, of course!) in a stream nearly the width of the sidewalk, with a depth of several individuals. I did not see it from the beginning, but I estimate it took about 15 minutes for them to reach the other side. It was most similar to watching schooling fish, but in slow motion. I assume this is adaptive behavior for the same reason as schooling and herds? This was at 8 AM on a very humid day, if relevant. Any idea as to species? Have you heard of this before? Is swarm the right term?
Signature: Seth

Dear Seth,
This fascinating phenomenon is an aggregation of Fungus Gnat Larvae in the family Sciaridae.  We generally reserve the term swarm for winged species while in flight.

Letter 6 – Dark Winged Fungus Gnat

pesky little bug
Hello bug people.
I have never used your site before, so I am excited to see how it works. This little bug, (that is a penny), is flying around my house. I am suspicious that it is the male of a scale insect that I am wrestling with on my plants. Does that seem possible or likely to you? Thanks.
Betsy Higgins
Florence, MA

Hi Betsy,
Our site works, if that is how you would like to refer to it, with the reception of emails. Then, depending upon our time, we try to post a few letters. We choose letters based on their content and imagery. Engaging writing always catches our attention. Interesting imagery also catches our attention. Unusual new species catch our attention and timely sightings most always get posted. We can assure you this is NOT a male Scale Insect. We believe it looks like a Dark Winged Fungus Gnat in the family Sciaridae. BugGuide has many examples and identifies only one to the genus level. Though they are annoying, they are harmless. The larvae feed on fungus and decaying organic matter. There is one image on BugGuide that illustrates both the abdominal shape and markings of the specimen in your image. We last posted a letter to our Gnat page in 2005, and that was a decisive factor in selecting your letter. More than that, we were amused that the penney in your photo is 50 years old.