The Impact of Great Diving Beetles on Pond Ecosystems

Great diving beetles are excellent pests, but introducing them to garden ponds needs a bit of consideration. Read this article to learn all about it. 

Great diving beetles are excellent for controlling water pests and for keeping a water body clean. This makes them highly beneficial. 

Since diving beetles can be kept as pets in aquariums, great diving beetles should be a great addition to a garden pond, right? Well, not always. 

While they make the ponds clean, these beetles can be a significant threat to some of the species in your garden pond. 

This article contains all the information that you will need to consider before adding these beetles to your garden pond. 

Where Do Diving Beetles Live?

As the name suggests, predaceous diving beetles prefer an inland aquatic habitat. They stay in ponds, billabongs, slow streams, and lakes

In some cases, they can also stay in mildly saline waters, but usually, they prefer clean, fresh water. 

When residing in larger water bodies, they often choose to stick near the vegetation growing around the shoreline to avoid predators like fish, frogs, and water spiders. 

Adult diving beetles hunt in these water bodies and eat other insects that live or accidentally fall into the water. They can also hunt small fish and tadpoles. 

Once they catch bigger prey, they tear it into small chunks before eating. 

The diving beetle larvae also live in the same water bodies and are voracious predators. 

Are They Beneficial To Ponds?

Diving beetles are considered beneficial for the ponds due to the fact that they eat almost all kinds of water pests, including snails, tiny frogs, salamanders, and more

These aquatic beetles also feed on dead insects in water bodies. This makes them a great way to keep the pond clean naturally. 

Diving beetles are also great hunters of the dreaded mosquito larvae that grow around water bodies. Therefore having them near a pond is excellent for pest control.

Another significant advantage of having these beetles in ponds is that the diving beetle population in water bodies helps to determine a lot about the health of the water. 

These beetles cannot survive if the water body is too polluted with salts and other chemicals. 

They need clean and well-oxygenated water. Therefore by studying diving beetle health in the water body, one can determine the quality of the water.  

What Problems Can Arise By Keeping Them In Garden Ponds?

The diving beetles are not a good fit for garden ponds if they have fish in them. They can’t co-exist with fish. 

Fishes in such an aquatic habitat will easily hunt these beetles and eat them. 

On top of that, a fish produces chemical cues, which scare beetles by telling them that there is a dangerous predator in the aquarium

Hence, they will avoid and escape your garden pond. In some cases, the bigger adult beetles can hunt small live fish. 

Also, having these beetles in your garden ponds will slowly eliminate frogs as the diving beetle larvae actively consume tadpoles as well.

Diving Beetle

Are They Dangerous To Humans?

Adult diving beetles and larvae are capable of biting people, but the bite doesn’t cause any severe harm. 

The toxins and digestive juices transferred through the bite are not strong enough to make a human sick. 

However, you might get a little intimidated when you see a bunch of these beetles in a pond swimming near you. 

Also, if the bite triggers an allergic reaction in your body, seek medical attention immediately. 

The diving beetles are attracted to light sources. As a result, they might come to your home if you put them in your garden pond. 

It can get a little annoying to have these beetles flying around your house, creating a nuisance. 

But rest assured, they are not dangerous in any way and will go back to the water pretty quickly because they can’t survive for very long without it.

But there is no need to be scared of them. In fact, they can be great for eliminating the pests like mosquito larvae near your home. However, if you are having issues that you feel you need a professional for call the number below.

Frequently Asked Questions

Do fish eat water beetles?

Yes, in an aquatic environment, fish hunt and eats water beetles. The water beetles are a good source of protein for these predators. But in some cases, the tables turn. 
Many giants and predaceous diving beetles can hunt and eat small fishes. These diving beetles are also capable of hunting tiny frogs, snails, and more.

Do great diving beetles live in water?

The great diving beetles prefer to live in freshwater habitats that contain still or slow-running water. 
These beetle will also be found in freshwater lakes with an abundance of aquatic plants and vegetation. They are found in the regions of Europe and Northern Asia.

Do diving beetles eat tadpoles?

Yes, the diving beetles actively consume tadpoles and other aquatic creatures like snails, insects, fish, and more. The beetle larvae also hunt and eat tadpoles. 
In fact, tadpoles are considered one of the favorite prey of the diving beetle larva. They use their sickle-shaped jaws to pierce into the tadpole’s body to inject digestive enzymes that help to liquefy their insides. 
They then suck the juices out and leave the carcass behind.

Do diving beetles eat pond snails?

Yes, the diving beetles are capable of hunting and eating pond snails. Therefore, you must not add diving beetles to your garden pond if it has snails. 
The diving beetles and the larvae are good predators and will probably eradicate the snails from your little garden pond. These beetles are also capable of hunting tiny frogs, small fish, and other aquatic insects.

Wrap Up

Adding great diving beetles to your garden pond without adequately knowing them is not a wise move. 

These beetles are beneficial as aquatic cleaners and pest eliminators, but you must know how and where to keep them as a pet. 

We hope this article helped you solve that puzzle. Thank you for reading the piece.

Reader Emails

Some of our readers wanted to understand the role of the great diving beetle in the aquatic ecosystem, which is the germ behind this article.

Go through the original letters and also watch some of the pics from our readers below!

Letter 1 – Predaceous Diving Beetle from Bali


November 29, 2009
A beetle or cockroaches picture taken in Bali Indonesia.
Bali Indonesia

Predaceous Diving Beetle from Bali
Predaceous Diving Beetle from Bali

Hi Nick,
This looks like a Predaceous Diving Beetle.  BugGuide has images of a North American species in the genus Dysticus that looks similar, but we are uncertain as to your species or genus.

This beetle belongs to genus Cybister but is almost impossible to identify which species because then you would need picture taken from above and down but you can also try to google indonesian cybisters.

Letter 2 – Predaceous Diving Beetle


Very large early spring beetle
April 2, 2010
Very large early spring beetle
I found this large 3.5-4 inch beetle in my yard on 3/31/10 in Traverse City Michigan (Northern lower penninsula). I have never seen such a large beetle! It was in the yeard in the dry (no rain this spring) dirt near the yard. Very rural area. We do own horses but it was atleast 500ft from the horses’ yard. It was a medium brown/tan in color. The wings were open and the beetle’s wings appeared injured. It had no horns and a small mouth. Is it some sort of very large dung beetle?
Traverse City, MI

Predaceous Diving Beetle

Dear Angela,
Your photo is quite blurry, but this appears to be a Predaceous Diving Beetle in the family Dytiscidae.  See BugGuide for possible genera.

Letter 3 – Giant Diving Beetle


Weird water beetle.. thing..
Location:  Oklahoma City, Oklahoma
August 5, 2010 5:35 pm
Hi, I recently moved to Oklahoma and I’ve already seen many interesting bugs around. We have an above-ground pool in our back yard that had been covered for 6 months and hadn’t been cleaned yet, and after uncovering it, I saw some weird bugs swimming around under the water. I noted the large back legs that it swam with and how it would shoot up to the surface from time to time to get some air, bringing a bubble down with it attached to the behind of it’s abdomen while it searched for food at the bottom of the pool. I caught the largest one I could find in a cup and saw that it looked kinda like a beetle. Can you tell me what the heck this is?
Westin Hacker

Predaceous Diving Beetle

Hi Westin,
This is a Predaceous Diving Beetle in the family Dytiscidae, a family well represented on BugGuide.  Perhaps one of our readers can provide more specific information regarding the genus or species.

Predaceous Diving Beetle

One of our regular contributors, mardikavana, has supplied us with the species name of Cybister fimbriolatus, the Giant Diving Beetle.  According to BugGuide its range is  “Eastern and central North America: from Nova Scotia south to Florida, west to North Dakota, Texas”  and its habitat is “Aquatic: ponds, usually deep water. Comes to lights.

Letter 4 – Predaceous Diving Beetle


Subject: Predaceous Diving Beetle
Location: CT
June 3, 2013 6:24 am
Recently I sent a pic of this former mystery bug, just wanted to save you some time in that I found the ID. Thank you anyway, and I really enjoy your site.
Signature: Cheryl

Subject: Mystery Bug
Location: CT
May 31, 2013 12:51 pm
Hello, I found this bug close to my fish pond here in CT, at first I thought it was a waterbug, but the front legs look different from what I’ve seen before. It could fly, and it had a ungainly and awkward way of crawling. Never seen one of these before, is it a type of waterbug?
Signature: Cheryl

Predaceous Diving Beetle
Predaceous Diving Beetle

Hi Cheryl,
We just returned to the office to find 100s of identification requests, and we know we cannot ever read them all.  We search for good subject lines, and though you originally requested our assistance, and we failed you, we are happy you did identify your Predaceous Diving Beetle and we are thrilled to be able to post your fine photograph.

Predaceous Diving Beetle
Predaceous Diving Beetle


Letter 5 – Predaceous Diving Beetle


Subject: What’s this bug?
Location: Connecticut
July 12, 2016 7:20 pm
Found crawling in yard in CT today, July 12, 2016. Can you help identify? I’m thinking some kind of beetle.
Signature: Rich P

Diving Beetle
Predaceous Diving Beetle

Dear Rich,
This is a Predaceous Diving Beetle in the genus Dytiscus, possibly Dytiscus harrissii that is pictured on BugGuide.  Its range, according to BugGuide, is “transcontinental in Canada, also in the northeastern US and Alaska; most common in the east (in the Great Lakes region), rare in the west.”  Of the entire genus, as this might be a different species, BugGuide notes the habitat is “permanent or temporary freshwater ponds and pools …, plus streams and rivers; usually found on or among aquatic plants” and “adults fly from March to November (varies by species).”  Though this is an aquatic predator, they are capable of flying from pond to pond.  

Letter 6 – Giant Diving Beetle


Subject: Large Army Green Beetle
Location: Terlingua Ranch, West Texas
May 5, 2017 2:37 pm
We found this guy on top of our water catchment barrel in West Texas, next to Big Bend National Park. He was big enough to fit in a teaspoon, which I used to get him out. He sprang off the spoon with those powerful back legs. He didn’t attempt to fly, but it looks as if it has wings of some sort under that hard exterior. I am certainly curious about this one. We see so many unique insects out there, but this one is a mystery. I love his little eyes….
Yes, I did take this photo and you can use it if you would like.
Thank you for any info you could give.
Signature: Jo

Giant Diving Beetle

Dear Jo,
This is a Predaceous Diving Beetle in the genus Dytiscus, and it is an aquatic species that can also fly from one watery environment to another, so finding it on the water catchment barrel makes perfect sense.  At first we thought it must be the Giant Green Water Beetle,
Dytiscus marginicollis, but that species is only reported from the far west, and according to BugGuide:  “posterior yellow band of pronotum broad especially in the middle” and your individual is lacking that band.  Based on this BugGuide image, we now suspect it might be Dytiscus carolinus, though other images of the species show strong grooves in the elytra.  It is described on BugGuide as being “Abdominal sterna colouration reddish to black and elytra with no yellow subapical transverse fascia.”  But for the coloration, that description does fit.  This FlickR image also resembles your individual.  So though we cannot commit to a species, we are confident that this is a Predaceous Diving Beetle in the genus Dytiscus.  Perhaps mardikavana who frequently writes in with identifications might be able to provide a species identification, however we have a previous comment from mardikavana that states:  “I can’t definitely ID it because when you are dealing with dytiscus sp. you need to see the underside as well. “

Correction:  May 14, 2017
Thanks to a comment from Zach Bruder, we learned this is a Giant Diving Beetle,
Cybister fimbriolatus, and according to BugGuide:  “Similar to Dytiscus, but metatarsal claws different. Elytra and pronotum smooth in male. Dilated male protarsus differs in details from that of Dytiscus. Female Cybister has fine furrows on pronotum.”  Here is a BugGuide image of a greenish individual.

Letter 7 – Predaceous Diving Beetle


Subject:  What kind of beetle is this?
Geographic location of the bug:  Tri-state area: MI, IN, OH
Date: 03/27/2019
Time: 07:18 PM EDT
Your letter to the bugman:  I found this insect dying on my deck (though the dog may have put it there). I’ve never seen one like it, much less at the end of March when very little is moving here yet. I assume it’s a beetle of some kind, but Google isn’t much help.
Thanks for answering my curiosity if you have the time! 🙂
How you want your letter signed:  Curious Gardener

Predaceous Diving Beetle

Dear Curious Gardener,
This is a Predaceous Diving Beetle in the family Dytiscidae, but we are uncertain of the species.  You may read about Predaceous Diving Beetles on BugGuide.


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10 thoughts on “The Impact of Great Diving Beetles on Pond Ecosystems”

  1. This beetle belongs to genus Cybister but is almost impossible to identify which species because then you would need picture taken from above and down but you can also try to google indonesian cybisters.

  2. These guys are edible. I doubt that they’re eaten in Indonesia, but they’re pretty popular in: Thailand, Cambodia, Hong Kong and Southern China [i.e. Guangzhou?]. I tried them in Thailand; they’re fishy.

  3. This id definitely a Cybister. Males have modified protarsus, used for grasping female during mating but it’s little bit hard to see the front legs so I can not tell whether it is male or female. But the species should be Cybister fimbriolatus.

  4. Hey Weston, if incase you still come across these Cybister Fimbriolatus, would you be willing to ship 1 or 2 of them to me in California?


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