Diving beetles are unique species of insects that live most of their lives underwater. But what do these little guys eat? Do they feed in the water or on the ground?
The beetle family is huge; it consists of around 400,000 known species. This makes them one of the largest insect populations in the world.
They are found in different corners of the world but did you know that some of these beetles are known for being able to live underwater?
In this article, we will talk about a species of beetles that are experts in diving underwater for long durations: the predaceous diving beetles.
These beautiful creatures are not just unique; they can also be kept as pets in your aquarium. But how? Let us find out.
What Are Predaceous Diving Beetles?
Predaceous diving beetles (also known simply as diving beetles) are a large group of aquatic beetles from the Dytiscidae family.
As the name suggests, these beetles are found near big lakes and ponds. The diving beetles show an average growth of 0.39-0.98 inches in length and have six legs.
It might appear like they only have a single pair of front legs, but the other two pairs are hidden underneath.
The pair of hind legs are similar to flat boards that are highly useful for paddling. Also, if you look closely, you will notice that all the legs have some hair.
They get the name from their swimming behavior and the ability to dive underwater for long durations.
These water beetles carry a bubble of air on their wings while diving. They return to the surface when the air bubble runs out.
An adult diving beetle can stay underwater for an extended period. You will be amazed to learn that they have clocked 36 hours of staying underwater!
The beetle larvae look like long centipedes with six legs. These guys hatch underwater and live there.
These larvae have pincers near their mouths, allowing them to catch and eat aquatic insects.
The diving beetle larvae are also known as the water tiger due to their predatory instinct and aggressive nature.
While the adult diving beetles carry air bubbles for oxygen, the larvae take air using the breathing pores present on their abdomen since they have to live underwater permanently.
What Do They Eat in Nature?
The diving beetles are scavengers and enjoy eating dead insects, earthworms, and small meat pieces. They are also capable of catching living aquatic creatures like fish and tadpoles.
The adult diving beetles often tear the larger prey into small chunks before consuming it.
A surprising fact about these beetles is that the dytiscid larvae can be cannibalistic in nature. Apart from eating their brothers and sister, they also hunt and eat snails, tadpoles, fish, and more.
The larvae hunt by injecting digestive juices into the body of the prey using the pincers. These juices kill and digest their hunt.
Are They Good As Pets?
These little beetles are an exciting element to add to your aquarium. Their body will give a bronze hue to your aquarium with silvery air bubbles and a great feeding display.
Also, they are comparatively cleaner than fish and require much less food. You can easily set up a n ecosystem in your aquarium that cleans itself with these beetles.
Make sure that you are adding a good quantity of aquatic plants and gravel. Do not install a filtration system here.
Avoid keeping fish and beetles in the same aquarium. Fish prey on small diving beetles and will readily consume the larvae.
Also, fish produces chemical cues through which the beetles can infer that there is a dangerous enemy in the aquarium. As a result, they will try to escape.
In many cases, giant diving beetles will kill and consume live fish.
Before setting up an aquarium with beetles, make sure that you cover the top of the aquarium, as these beetles can easily escape, especially during nighttime.
How To Catch Them In Nature?
There are around 4,000 different diving beetle species scattered throughout the world, and you can easily find them near water bodies in a freshwater zone in a warm and humid climate. Listed below are a few techniques that you can use to collect these beetles for your aquarium:
The light trapping method
Diving beetles are attracted to bright lights, like many other insects. You can trap the insects at night by luring them to a light source.
You need to hang a white sheet in front of a light source and put it near a freshwater source. The bright light will attract the diving beetles, and you catch them.
Using nets with a flat bottom
In this method, you need to use a rectangular, triangular, or D-frame net to catch these beetles. Gently put the net in a freshwater source and thrust it forward in an overhand motion.
Pull the net back along the bottom. This technique is highly effective in catching larger beetles that try to swim away from the net. You can purchase these nets in biological supply houses.
Creating bottle traps
Using bottle traps is another excellent method to capture these beetles. Here you add a small chunk of meat in a bottle trap to attract and catch a beetle.
You can create one using a large soda bottle. Cut the top portion and place it in an inverted manner on top of the other half.
To secure the gap, make sure you staple it correctly. Place a small piece of meat in with styrofoam to keep air slits on top of the water. Place it in a pond or freshwater source and leave it overnight.
Frequently Asked Questions
What do diver beetles eat?
Diver beetles are carnivores and active consumers of aquatic insects. These beetles are scavengers, and they love to feed on dead insects, small meat pieces, earthworms, and more. In some cases, they also hunt snails, tadpoles, and small live fish.
Do diving beetles eat algae?
Diving beetles might be either herbivore or not. The ones that are herbivores can eat algae as well as other types of aquatic fauna, their stems, and plant sap.
Does the great diving beetle bite?
The Great diving beetles can bite, but they rarely do so. But you must be careful around them as their bites can be painful.
Thankfully, the toxins and digestive enzymes released during the bite are not capable of causing significant problems to the massive body of humans and pets like dogs.
How long does a diving beetle live?
Each predaceous diving beetle can live up to several years. They have a complete life cycle that consists of all four stages from the egg to larva, pupa, and finally, as an adult.
These beetles are aggressive hunters from the larva stage itself and usually consume and prey on aquatic insects, tadpoles, and more.
Diving beetles are a fascinating species of insects, and despite their highly aggressive nature toward their prey, they can be a valuable addition to your aquarium and be your new pets.
We hope this article helped you understand the habitat and the behavior of these insects. Also, we believe this article can be useful as a small guidebook for those who want to keep these beetles as pets.
Thank you for reading!
Diving beetles can make for great pets, so it is no wonder we have received several such questions over the year about their food, diet, habitat, etc.
Please go through some of the letters below from our readers and get some advice from them as well.
Letter 1 – Predacious Diving Beetle
I was on the roof of my place of employment. When I came across this Bug that I have never seen before. I am hoping you will be able to identify it. Thank You
This is a Predacious Diving Beetle in the genus Dytiscus, and like many aquatic insects, it can fly.
Letter 2 – Predaceous Diving Beetle
Unknown flying beetle? May 20, 2010 Hello everyone, Great pictures and information here. We found this bug on the deck in the morning, possibly drawn to the night light. It has some trauma from the birds pecking at it. It is quite large about 2cm wide and 4cm long. It has large wings almost 3cm long and back legs. I hope someone can help us identify this bug. Sue and John Southern Ontario Canada Dear Sue and John, This is a Predaceous Diving Beetle in the genus Dysticus. Though they are aquatic, they can also fly and are attracted to lights. BugGuide has wonderful information on the genus.
Letter 3 – Predaceous Diving Beetle
A green and gold scarab? Location: Shelby, MT September 6, 2010 5:51 pm Dear Bugman, I live in Montana and recently found this bug crawling across my dog. *ick* Upon closer examination the insect seemed to be iridescent with a green and gold color…with a little gold V on his head. Please I would absolutely love to know what this is…. Signature: Melissa Hi Melissa, This is a Predaceous Diving Beetle in the genus Dysticus, and we wonder if perhaps your dog was swimming in a pond just prior to your discovery. We believe this may by Dysticus dauricus, which we located on the Entomology Collection website of the E.H. Strickland Entomological Museum of the Department of Biological Sciences at the University of Alberta. The Entomology Collection website describes it as: “Large (29.7 to 40.0mm), broadly elongate (Larson et al. 2000). Black – some with green appearance. Basal antennal segments yellow, darker and reddish terminal segments. All pronotal margins bordered with yellow. Females with reddish or brown-black striae and black ridges. Reddish yellow or reddish ventral surface, except red metacoxa, medially brown-black metasternum, and black anterior and posterior margins of abdominal sterna. Brown-black or black sternal basolateral maculation – progressively smaller to posterior. Yellow or reddish legs.“ Interestingly, we overlooked this species when we were searching BugGuide because the photos there look quite different than the photo on the Entomology Collection website. The Giant Green Diving Beetle, Dytiscus marginicollis, on BugGuide just didn’t seem right. BugGuide does indicate that Dysticus dauricus is “the largest North American dytiscid.” The Entomology Collection website also has this fascinating information of the diet of Dysticus dauricus: “Predatory – active swimmers (Larson et al. 2000). Invertebrate and fish larvae prey. Records of larval cannibalism and predation on salamanders and snakes in Arizona (Holomuzki 1985, 1986).” Perhaps Mardikavana can confirm our identification. Thank You so very much. He was actually not swimming but we have had quiet a bit of rain and I think maybe somehow when I took the dogs outside (both English Mastiffs) he attached himself somewhere out there. Once again…thank you. I spent hours trying to place him. Melissa
Letter 4 – Predaceous Diving Beetle
Strange black beetle Location: City, Worcester,Ma. May 25, 2011 11:50 pm Hello… I found a smooth shelled black beetle about 2 to 2 1/2 inches long. I have never seen a beetle like this one…it looks to me to be maybe a water beetle of sorts. I have been studing insects most of my life and I use your site very often to help me idendify strange insects. I live in central massachussets and I was at work during the night shift when spotted this little fellow crossing some concrete roadway in our plant. It would be wonderfull if you could tell me what this guy is.. I left him alone after I snapped these pic with my phone. Thank you,Dennis Lynde Signature: Dennis Lynde Dear Dennis, This is a Predaceous Diving Beetle in the family Dytiscidae (see BugGuide). It is most likely in the genus Dytiscus.
Letter 5 – Predaceous Diving Beetle from Germany
Subject: never seen it before.. Location: Bad Dürkheim, Rhineland Palatinate, Germany March 9, 2014 3:40 pm hey bugman! I am from Germany, exactly from Rhineland Palatinate. So I opend the trunk of my car yesterday and a huge bug just lay there.. It tried to cover up, I guess. It was already dead when I found it. I have never seen something like this! Really big and colour was golden and green, it also got huge eyes. It would be awesome if you know what kind of bug it is! thank you! Sarah Signature: Sarah Hi Sarah, This is an aquatic beetle, most likely a Predaceous Diving Beetle in the family Dytiscidae. Like many aquatic insects, Predaceous Diving Beetles are capable of flying from one body of water to another. Your individual bears a resemblance to Cybister laterimarginalis, a European species that is pictured on the Polish website Iconographia Coleopterorum Poloniae and on Wikimedia Commons.
Letter 6 – Predaceous Diving Beetle or Giant Water Scavenger from Serbia
Subject: big black thing Location: Belgrade, Serbia March 22, 2017 7:47 am This just fell from the sky with a loud thump and doesn’t move. I’m 46 and I’ve never seen one. Signature: Milan Maksimovic Dear Milan, Though this is an aquatic predator, the Predaceous Diving Beetles in the genus Dysticus, and we believe your individual is in the genus Dysticus, are capable of flying from pond to pond in the event the original pond begins to evaporate. Here is a BugGuide image for comparison. Thanks Daniel! This was far from any still or flowing water, by at least 3-4 miles. It’s possible that some bird picked it up and dropped it since it fell in a straight line from the sky. Thanks again. Yes, that is possible.
Letter 7 – Predaceous Diving Beetles
Subject: Crazy looking flying something Geographic location of the bug: Bellingham washington Date: 10/24/2017 Time: 12:33 PM EDT Good day, I was outside just as it was getting dark and I heard a weird bug flying around. Well it was a big something and then I notice a few more over by the house. It’s fall time here and nights get down to the 40’s. I am sending a phone I took please feel free to use it. How you want your letter signed: TJA Dear TJA, These are Predaceous Diving Beetles in the family Dytiscidae, but it is going to take someone with more expertise in the family to provide you with a species identification. Though they are primarily aquatic, as you observed, they are capable of flight. According to BugGuide: “Adults with long hairs on hind tibiae and other modifications for swimming; move their hind legs together like oars, like Backswimmers do.”
Letter 8 – Predaceous Diving Beetle
Subject: What kind of beetle is this? Geographic location of the bug: Western New York Date: 07/07/2020 Time: 10:33 PM EDT Your letter to the bugman: There is a large beetle looking bug out this evening. 1.5-2 inches in length, oval body, big round eyes and the shell is green, black/blue and brown. How you want your letter signed: M Dear M, This is a Predaceous Diving Beetle in the family Dytiscidae, probably in the genus Dytiscus, and possibly Dytiscus fasciventris which is pictured on BugGuide and described as: “only the anterior and lateral margins of pronotum are bordered by a broad pale stripe (posterior margin not bordered); lateral margin of elytron bordered by broad pale stripe on basal half only remainder of dorsal surface brown, brownish-black, or green; ventral surface yellow to reddish except metacoxa yellow and metasternum brownish-black medially.” Though they are aquatic, Predaceous Diving Beetles can fly from pond to pond and they are sometimes attracted to lights. Awesome response time haha! Thank you so much! Our timing aligned.
Letter 9 – Predaceous Diving Beetle
Subject: Bug in pool skimmer basket Geographic location of the bug: Stratham, NH Date: 04/11/2021 Time: 02:52 PM EDT Your letter to the bugman: Found this giant in my pool skimmer basket this morning. Curious to know what it is. How you want your letter signed: Pool owner Dear Pool owner, This is a Predaceous Diving Beetle in the family Dytiscidae, probably in the genus Dytiscus. According to BugGuide the habitat is “permanent or temporary freshwater ponds and pools (D. marginicollis may occur in saline ponds), plus streams and rivers; usually found on or among aquatic plants.”
8 thoughts on “What Do Diving Beetles Eat?”
I can’t definitely ID it because when you are dealing with dytiscus sp. you need to see the underside as well. But I can say that this is a female and a rarer version because females usually have furrows on their elyctra.
Thos is actually Cybister sp.
Thanks for the correction mardikavana.
I want to know in details of the biology of the Cybister species atleast the Indian species.
I am rearing them in crude way and moving with a great scarcity of Taxonomist in this field.
i have photographs but I don’t know the method of uploading it here.
Use the Ask What’s That Bug? link at http://www.whatsthatbug.com/ask-whats-that-bug/
mine one is only 1cm long and looks white during initial stage of metamorphosis while changed into adult form from nymphal ? stage(a deep brown segmented creature with crusty covering like millipedes.
This is great diving beetle (Dytiscus marginalis) male. I really appreciate picture of the ventral side because you can see structures that differ this specie from other smilar species like D. circumcinctus.
Thanks for the correction Mardikavana.