We’re all aware of beetles that raid our pantries and feed on our crops, but did you know that some beetles prefer to live in water? The diving beetle is a unique creature that you simply must know about.
The diverse world of insects is always interesting, but aquatic insects are a special bunch.
This is probably just because their aquatic habitat makes them seem a bit more exotic than the land species we’re more acquainted with.
Diving beetles tread the line between aquatic and land-dwelling as though they never knew a difference existed!
These babies are born in the water and spend most of their lives in it, but they are found on land as well.
Read on to learn more about this unique, confounding, and beautiful beetle.
What Are Diving Beetles?
Diving beetles, or predacious diving beetles, are a family of water beetles that earn their name due to their ability to dive underwater.
Scientifically known as Dytiscidae, this family comprises more than 4,000 species.
While they don’t usually fly over long distances, the diving beetles are adept swimmers. The streamlined structure of their bodies allows them to move swiftly through the water.
Interestingly, their eyes have bifocal lenses that allow them to find water bodies more easily while migrating.
Diving beetles are carnivorous insects that prey on various other aquatic organisms to sustain themselves.
What Do Diving Beetles Look Like?
While diving beetles share the dome-like shape that beetles are known for, their structure is a bit different from the beetles we’re more familiar with.
As mentioned earlier, diving beetles have streamlined bodies that suit their aquatic habitat better.
They’re rather fat and oval, with the rear portion being wider than the front part. These beetles are two inches long on average, but some species are larger.
The great diving beetle, for instance, grows up to three inches and is one of the largest aquatic insects.
The color varies from one species of diving beetle to another, with most of them being tan, black, or olive green. While they’re primarily of a solid color, there are exceptions.
The sunburst diving beetle, for instance, has a black body with several large bright yellow spots.
Many diving beetles, including the sunburst diving beetle, also have a carapace of a different color – usually orange or yellow. Such an appearance makes diving beetles easy to identify.
Diving beetles have well-developed compound eyes that serve them well while hunting for prey. They also feature chewing mouthparts and a pair of short and thin antennae.
Special Adaptations in the Diving Beetle
The diving beetle is not only an aquatic insect but also a predator. This calls for special adaptations to suit its habitat and feeding habits.
Apart from the streamlined structure for efficient swimming and diving, they’re also capable of storing oxygen. This is how they survive while hunting underwater.
They carry air bubbles under their wing cases, known as physical gills. Although they can refill the oxygen reserves with oxygen extracted from the water, they consume the stored oxygen at a faster rate.
Eventually, they have to come to the surface and refill the bubble.
Interestingly, these beetles have a completely different way of surviving underwater in the larval stage.
Known as water tigers, diving beetle larvae have a snorkel-like organ to breathe while submerged.
Another important characteristic of these beetles is the appearance of their hind legs. While they have three pairs of legs like any other insect, the hind legs are particularly large and oar-shaped.
These powerful legs allow them to push through water with ease. The hind legs also have a thick fringe of swimming hairs that make them even more suited for the purpose.
Where Do They Live?
These interesting aquatic beetles are more common than you might realize.
You can find them in every continent besides Antarctica, though the species vary from one region to another. North America alone has more than 500 species of diving beetles.
They live in shallow water bodies, which makes them even more common in pools, lakes, and streams.
In larger water bodies, they mostly stay among the vegetation close to the shore – away from fish that can potentially prey on them.
Diving beetles prefer still or slow-moving waters and have adapted to almost every type of inland aquatic environment, including brackish water.
What Do They Eat?
Adult diving beetles are surprisingly good predators, capable of hunting prey larger than themselves.
While they primarily feed on other invertebrates, tadpoles and fish are among their food sources too. Diving beetles chew and tear their prey into manageable pieces if they’re too big.
If live prey isn’t available, you can also find them scavenging for carrion.
Diving beetle larvae share a similar range of food sources and are also adept predators.
Their voracious appetite and effective strategy of ambushing their prey have earned them the title ‘water tigers.’
The larvae lie still in wait for their prey, grabbing them and injecting them with toxic digestive juice as soon as they get close.
The juice kills the prey and digests them partially, after which the water tigers consume the liquified remains.
What Is the Lifecycle of Diving Beetles?
The Predaceous Diving Beetle has a similar life cycle as most insects, with four prominent stages – egg, larva, pupa, and adult beetle. However, the larval stage deserves special mention due to the larvae’s ability to hunt.
- Eggs: While diving beetles are aquatic insects, they don’t lay eggs in the water. Instead, the females lay them on vegetation on or above the surface of the water. Often, they choose spots close to frog egg clusters so that the tadpoles can sustain their larvae.
- Larvae: The larvae drop into the water upon hatching. They prey on insects, insect larvae, crustaceans, small fish, tadpoles, etc., while molting through the instars.
- Pupae: Once the larvae have finished the final stage of molting, they move out of the water and burrow themselves in mud. Here, they begin to pupate. This duration of the pupal stage may vary from a week to several weeks.
- Adults: Once the metamorphosis is complete, adult diving beetles emerge and return to the water to continue their life cycle and reproduce.
Dytiscid beetles can live for several years. In cold regions in the northern hemisphere, they hibernate in frozen water bodies during the winter.
Where Do They Lay Eggs?
Adult diving beetles lay eggs on aquatic plants on or above the water’s surface.
They choose the location such that the larvae hatching from those eggs can drop into the water easily. In many cases, they also cut into stems and secure the eggs strongly in place.
Can Diving Beetles Fly?
Members of this aquatic beetle family are capable of flight. Their hard elytra open up sideways to release the soft, membranous hindwings.
In most cases, they just fly around locally to move to a different water body when the current one becomes unsuitable for their survival.
Do Diving Beetles Bite or Sting?
Although diving beetles don’t have stingers, they can still bite you with their chewing mouthparts.
A diving beetle bite is painful, but they rarely bite at all. Besides, the pain usually subsides quickly and doesn’t leave any lasting effects. The same applies to their larvae, the water tigers too.
Are They Poisonous or Venomous?
Thankfully, diving beetles do not carry any poison or venom potent enough to hurt humans. Even if you get bitten by a larva or an adult, there’s no need to worry or seek medical attention.
The toxic digestive juices secreted by water tigers are effective only against the small organisms they prey on. It’s harmless to both humans and pets.
Are They Harmful to Humans as Pests?
Apart from the chances of getting bitten by a diving beetle, they aren’t harmful to humans. Diving beetles count as beneficial insects due to their predacious nature.
They can feed on mosquito larvae and other unwanted pests and pest larvae in a pond, thus reducing the need for pest control treatments.
However, if you’re trying to grow the toad population in your pond, diving beetles may pose a problem by hunting the tadpoles.
Can They Come Inside Homes?
As diving beetles live in aquatic habitats, you don’t have to worry about them coming inside your home.
They spend most of their time in a water body, flying only when they need to migrate. In case a diving beetle ends up in your home, it did so on accident.
What Are Diving Beetles Attracted To?
Diving beetles are attracted to artificial lights, which is why they often end up in man-made pools.
If you’re trying to attract diving beetles to your pond, maintain good water quality as they seek well-oxygenated water.
How To Get Rid of Diving Beetles?
Unless they’re in a swimming pool or creating an imbalance in the ecosystem of your pond, there’s no need to get rid of diving beetles.
However, if you have to do it, using a strainer to remove the beetles manually is the easiest way.
Don’t spray any insecticides in the water – it will harm the other life forms in the pond or individuals entering the pool.
What Eats Diving Beetles?
While straining them out of the pond is a good idea, another way is simply to let natural predators do the work for you.
When they are young (as in their larval stage), fishes, skunks, and raccoons like to have a go at them by picking them out of the water’s surface.
Fish are by far their biggest enemy, and most larger fish eat both larvae and adult diving beetles.
However, since the adults spend some time on land as well, they are often prey to larger birds and reptiles like geckos and lizards as well.
As we can see, diving beetles are beneficial natural predators that can help keep your pool or pond free of unwanted pests.
Whether as larvae or as adults, these bugs are always on the lookout for a good meal – and all your aquatic pests are a form of food for them.
Finding these beetles in a water body is also a good sign, as they prefer clean water with ample oxygen content.
Thank you, reader – we hope it was an enjoyable read.
Letter 1 – Large Diving Beetle
Great site guys thanks
Thank you for being on the web. My son (9) and I have used your site to identify two new beetles I have never seen before. We now have a longhorn and a Large Diving Beetle. Would you like to have a clearer digital photo of the Diving Beetle for your site.
Peter & Jonathan Turner
Hi Jonathan and Peter,
We are thrilled to have your clearer image of a Large Diving Beetle, Dytiscus species. Thank you so much.
Letter 2 – Predaceous Diving Beetle
November 5, 2009 A co-worker of mine knows a little bit about my fascination with beetles, bugs, spiders and insects. The other day, he was arriving for day shift as I left from my night shift, and said “Wait, I found you something!” It turns out it was this guy, a black shiny hard shelled beetle almost an inch-and-a-half long. He was found early Halloween morning, on the street in Norwich, CT, pretty far from any water, but shortly after some heavy overnight rains. Perhaps he was washed out of a pond or creek. It appears to be a Dyticid – Cybister fimbriolatus according to Bug Guide: http://bugguide.net/node/view/59505 I put him in a large shallow container of water that was in my yard, neglected most of the fall and looked like it had some other small critters in it. He was a strong swimmer, head down and tail up the whole time. The back legs are hairy and very long, and seem to be used much in the way a frog swims. The hairs act a bit like a frog’s webbed feet. He was never aggressive and appears to have very small mouth parts, and large bluish eyes. I placed a quarter with him so you can get a sense of his size. In Connecticut, we don’t see a lot of bugs this late in the year, so I hope he has found a good place to spend the winter. We haven’t had a hard frost yet being near the coast so hopefully he will locate a good hiding spot. Rob Bareiss, New London, CT Hi Rob, We were a bit busy when your letter arrived, and it was overlooked. We agree that this is a Predaceous Diving Beetle in the family Dytiscidae and we are posting your wonderful letter and photo a few months late. Hey that’s cool! I’m glad you guys liked the pictures and that I was right with the identification. I’m still new to this but your site has sparked a revival of an interest that I have had for over 35 years! Take care and Happy New Year, Robert
Letter 3 – Predaceous Diving Beetle pets produce spawn!!!!!
Predaceous Diving Beetles July 9, 2010 I have been keeping 3 predaceous diving beetles in a large fish bowl for several months. This morning we discovered several clusters of eggs all over the stems of the aquatic plants in the water. I’m interested in raising the young, but I’m concerned that I might not be able to provide enough food to keep them alive. I’ve been trying to research food sources online, and have found nothing except maybe mosquito larvae that would work for the new beetle hatchlings. Any ideas? Mike Shreveport, Louisiana Hi Mike, Your insect-aquarium sounds so wonderful. Do you have a lid on the bowl? Predaceous Diving Beetles can fly quite well, but the larvae are totally aquatic and are known as Water Tigers. When they hatch, the young Water Tigers will most likely prey upon one another, eliminating the smallest and weakest. As they grow, you can probably feed them live tubifex worms or red worms which are also sold at most aquarium stores. Since they cannot fly, the larvae can also be placed in a larger container outside and they will be able to feed upon any mosquito larvae that develop in the tank. Newly born guppies will serve as a nice food supply as they begin to grow. Luckily, they will not need to eat daily. Good luck with this awesome opportunity.
Letter 4 – Predaceous Diving Beetle from UK
What is this Location: New Romney Kent May 27, 2011 3:20 pm Hi, I found this in the doorway of my car and I would love to know what it is. Signature: Greg Hall Hi Greg, We believe this is a Predaceous Diving Beetle in the Family Dytiscidae and furthermore, we are fully confident that mardikavana will be providing us with confirmation and perhaps even a species identification.
Letter 5 – Predaceous Diving Beetle
large beetle Location: southern Alberta Canada September 9, 2011 10:11 pm Hi Bugman I live in southern Alberta on the Praires, it is Sept 9, 2011, opened up the truck door and this large dark green beetle was crawling across the floor. Signature: Puzzled on the Praires Dear Puzzled on the Praires, This beautiful beetle is a Predaceous Diving Beetle in the family Dytiscidae, but we are not certain of the species as many member is the family look similar, as you can see if you browse through the images on BugGuide. Thank you very much for identifying this beetle. This year we have a large slough on the south side of our acreage, the Diving beetle probably came from there. I put it in my garden, guess I should have put it in the water. I was surprised when I found it in my truck, it must have flew in there. Again thank you, your bug web site is wonderful, we have lots, I mean hundreds, of dragonflies in the garden and I have looked up several of them on your site. Keep up the good work. Cheers
Letter 6 – Predaceous Diving Beetle
Wondering what this is? Location: Bemidji, MN (Northern MN) January 27, 2012 6:34 am Hello, My little 4 year old and I were trying to Google and identify this tonight. We were unsuccessfull so I’m writing to you for help. We took these pictures on 4/25/2011 at 10pm. It was outside our side door of the garage. We lived in the woods, thick with almost 40 year old red pines (planted as a tree farm, and then a couple homes were built within). Within a quarter mile is a small stream and wet land area. Hope this helps. Signature: Thank you! Krissy H.Dear Krissy, This is a Predaceous Diving Beetle, and as its name indicates, it is an aquatic insect, however, it is also capable of flight if its pond dries out, runs out of food, or it seeks a mate. It is in the family Dytiscidae (See BugGuide) and we cannot provide you with an exact species name, but perhaps Markikavana will write in with an identification. The predatory larvae of Predaceous Diving Beetles are sometimes called Water Tigers. Daniel, Thank you so much. I really appreciate it! I think I made a donation to your site the day you sent me this email, now I can’t find a receipt. Can you tell if I indeed made the donation, sometimes I sit down to do something and can finish it due to my 4 year old–he doesn’t like it when I’m on the phone or computer. Thanks again! Krissy Hughes Thanks for your kind intentions Krissy. We will copy our webmaster who keeps track of website finances to see if he can verify the donation.
Letter 7 – Giant Black Water Beetle, NOT Predaceous Diving Beetle
Large black beetle found 4/1/11 in Indiana Location: Hamilton County, Indiana April 2, 2012 10:56 am I found this beetle walking in the woods on April 1, 2012. It was in Hamilton County in Central Indiana at around 7:30pm. The photos aren’t the best because I only had my cell phone with me. In person, it had a beautiful irredescent green that ran down the middle of the back. The park has some creeks, a swamp, and a marsh, prairie and forest all in 127 acres. I would like to know the name of it to see if I can learn some more information about this insect I had never seen before so I could share this information with others if I see it again. Signature: Just curious Dear Just curious, This is an aquatic Predaceous Diving Beetle in the family Dytiscidae, and though we don’t get too many submissions of Predaceous Diving Beetles, the letter we just posted from California was also a representative of this family. See BugGuide for additional information on the family. We would love a professional opinion regarding the species. Correction: April 6, 2012 Thanks to a comment from MichaelH, we are linking to the correct species on BugGuide. The Giant Black Water Beetle is also known as the Giant Water Scavenger.
Letter 8 – Predaceous Diving Beetle
Big Beetle in Alberta already!? Location: Calgary AB canada April 12, 2012 11:25 am Hello, found 6 of these on my driveway last night around 10 pm. Signature: dont know what this means Your large beetle is an aquatic insect known as a Predaceous Diving Beetle in the genus Dytiscus, we are linking to the BugGuide page for the genus. Though aquatic, they are capable of flight which serves them well so they can fly to a new habitat if a pond dries out. Thank You very much for you prompt reply, much appreciated. Hopefully they find a pond with mosquitoes they can munch on. -Brandon
Letter 9 – Predaceous Diving Beetle
Subject: Big beetle in Maine Location: Small Point, Maine marsh next to ocean July 27, 2013 5:30 pm So, I found a bug in the road at a campground and ran it up to my son (since he loves bugs). He didn’t fly and gave my son a good pinch that drew blood. (Two little punctures) We’re just curious what it was. He was pretty big (the pic shows my husbands hand for reference.). Signature: Rebecca Hi Rebecca, This is a Predaceous Diving Beetle, an aquatic predator. They are not dangerous, but as you and your son found it, they can bite if carelessly handled. Though they are aquatic, Predaceous Diving Beetles can fly from pond to pond. awesome. it did give him a good bite, which led to blood (exciting!). we needed to know what type of bug so we can anticipate which superpowers he can be expecting. thanks!
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 – Large Diving Beetle
My husband and I found this beetle in our back yard. I have lived here on the North Coast of Oregon for 20+ years and have never seen one like it. He or she was under our dogs (kiddie) pool. Sorry for the bad pictures!
There is a good reason your beetle was found under the pool. It was probably once in the pool. You have a Diving Beetle, from the Family Dytiscidae and the genus Dytiscus. They can be recognized by their dark brown coloration with yellow along the sides of the prothorax and elytra. They are voracious predators that feed upon tadpoles, small fishes and insect larvae.