Water Beetle

Coleoptera hydrophilidae

Last updated: October 5, 2022
Verified by: AZ Animals Staff
© iStock.com/mirceax

Water beetles bite; they use their legs to inject venomous digestive saliva

Water Beetle Scientific Classification

Scientific Name
Coleoptera hydrophilidae

Read our Complete Guide to Classification of Animals.

Water Beetle Conservation Status

Water Beetle Facts

Tadpoles, small fish, insects, and snails
Name Of Young
Fun Fact
Water beetles bite; they use their legs to inject venomous digestive saliva
Shallow ponds or rotting vegetation
Birds, Fish, various mammals
Common Name
Water Beetle
Number Of Species

Water Beetle Physical Characteristics

  • Brown
  • Grey
Skin Type
2 to 3 years
1.5 inches

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View all of the Water Beetle images!

A water beetle is not a specific species; it’s just a generalized term for any beetle living in water at any time of its life cycle. While the majority of water beetles can only survive in freshwater, several marine species inhabit the littoral and intertidal zone.

There are an estimated 2000 species of true water beetles that inhabit various habitats throughout the world. Many water beetles have an elytra cavity, an air bubble located under their abdomens that supplies them with air, preventing water from infiltrating their spiracles.

Other species direct gas exchange with the water by modifying the surface of their exoskeleton to form a physical gill or plastron.

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Specific families of water beetles have fringed back legs equipped for swimming; however, many do not have this beneficial characteristic.

Three Amazing Water Beetle Facts!

  • Water scavenger beetles are aquatic beetles that make alternative movements with their legs, making it look like they are trying to run underwater.
  • Some water beetle species use an air bubble located under their abdomens to breathe as they swim. When coming up for air, they will surface head first.
  • Water beetles vary in size and can measure between 0.1 to 2 inches. Some species have fringe on their back legs, which help with their swimming capabilities.

Water Beetle Scientific Name

Water Beetle’s scientific name is Coleoptera hydrophilidae, and they belong to the order Coleoptera. The many insects in this order are the only ones with elytra, which are tough forewings used to protect their fragile hind wings.

Having elytra is beneficial because it enables these insects to adapt to many habitats like logs, soil, and leaf litter, which would usually damage the wings of other insect groups.

In addition, elytra cover most of the abdomen and thorax, making it appear like these water beetles only have two segments. However, upon closer inspection, they are made of three segments, the head, abdomen, and thorax.

Water beetles are members of the Hydorphilidae family, also known as water scavenger beetles. They are a family of primarily aquatic beetles. Their most distinguishing feature is the long maxillary palps, which are taller than their antennae.

Water beetle’s larvae are typically predatory, but adults can be herbivores or predators and are also scavengers. In addition, many members of this species can produce sounds.

Appearance: How to Identify Water Beetles

Water beetles are generally shiny and gray or dark brown in color. They are small beetles and only measure  1.5 inches in length.

Water beetles are often mistaken for oriental cockroaches that occur in Africa because they share similar characteristics. However, they are not the same and can be distinguished by their short, hairy antennae.

Habitat: Where to Find Water Beetles

Water beetles inhabit every continent on earth except Antarctica. However, they thrive in high humidity areas of four States in the USA:

  • Texas
  • California
  • Arizona
  • Florida

They prefer habitats found in marshy areas and underwater surfaces. Water beetles typically build their homes in shallow ponds or rotting vegetation. Adults are often referred to as Water Scavenger Beetles.

Diet: What do Water Beetles Eat?

They mainly eat decaying or dead aquatic plants, tadpoles, small fish, insects, and snails. When water beetles are still in their larvae stage, they typically feed on small fish and tadpoles found in their habitat. Adults have a more varied diet that consists of various aquatic insects and dead or decaying plants.

Do they Bite?

Yes, water beetles do bite; they use their legs to inject venomous digestive saliva. While water beetles’ bite is painful but does not require any medical attention because it is not technically a bite, it is just a tiny injection of non-fatal poison.

Water Beetle Predators and Threats

Water beetles have many predators that include animals like:

While there is an abundance of water beetles, which are not considered endangered, loss of habitat, climate change, pesticides, and impoundment are bound to impact their population numbers eventually.

Water Beetle Reproduction, Babies, and Lifespan

After mating, the female beetles will lay eggs on a bed of algae or in aquatic vegetation. Water beetles reproduce in late spring or early summer, and the females lay pale brown eggs.


Water beetles do not live long; some only make it a few months. However, their average lifespan ranges from 2 to three years.

How Do They Communicate?

Water beetles use sound and chemicals (pheromones) to communicate with one another. In addition, they also use sight to communicate, similar to fireflies. Other methods of communication include:

  • Scraping together their mouthparts
  • Rubbing their legs on their bodies

Seven Different Species of Water Beetles

There are around 2000 species of true water beetles that inhabit various habitats throughout the world. Each specie of aquatic beetle is unique in its own way and serves its own economic role. Some members of these species include:

1.      Whirligig Beetles

Whirligig beetles belong to the Gyrinidae family and are small to medium-sized beetles in the order of Coleoptera. They are freshwater beetles that inhabit lakes, streams, and ponds.

These beetles have flattened bodies, two sets of eyes that help them see above and below the water, and fringed gills on their abdominal segment.

They are fast swimmers and prey on dead insects found on the water’s surface. In addition, their legs are well adapted to help them maneuver through the water because they are flat and short. In fact, they have 3 pairs of legs; their front legs are longer than the rest, which helps them hold onto their prey, primarily invertebrates or insects.

Males have a unique characteristic known as suckers on their legs. These suckers help them grab and hold onto the slippery bodies of females during their mating ritual.

Female whirligig beetles lay their eggs on the surface of aquatic vegetation, and both males and females die soon after. These beetles typically measure 0.1 to 0.7 inches in length.

Some individuals will leave the water and fly away to avoid predators when facing danger.

2.      Screech Beetles

Screech beetles are a specie of water beetle that belongs to the family Hygrobiidae. They are native to North Africa and southern and western Europe in muddy, stagnant water.

They get their names for the harsh grating noise they make. To make the sound,  they rub the sharp edge of the 7th abdominal tergite against their subpical median file, located under the elytral.

They measure 0.3 to 0.45 inches in length, and their bodies are brown with distinctive markings. Their wing cases are a darker brown and leaf-shaped. In addition, they have black banding on their pronotum and head. Their antennae and legs match the coloring of the elytra.

Screech beetles are a common UK species that are often seen between the months of March and October in the margins of stagnant or still water bodies. Their preferred habitat is muddly lakes, streams, or ponds.

The males, females, and larvae are predators that prey on Tubiflex worm species, insects, and invertebrae. Screech beetles lay their eggs in a small row on the surface of aquatic plants, and they evolve into crustacean-like larvae that are solely aquatic.

Larvae breathe through gills and inhabit the bottom silt, accumulated detritus, and mud. Once the larvae reach adulthood, they submerge themselves in soil over the winter months.

3.      Skiff Beetles

Skiff beetles are a tiny family of water beetles, also known as Hydroscaphidae, which consist of 223 species. They are tiny, barely 0.079 inches in length. Their bodies are brown or tan, and their elytra are short, exposing several tapering tergites on the abdomen.

Skiff beetles have fringed wings with long setae, and the larvae have a broad thorax and slender abdomen. They live on algae carpets, usually with a thin layer of running water.

Generally, they inhabit the accumulated algae lining the edges of a stream of water. Not only is algae their habitat, but it is also their primary food source.

They are highly adaptable and thrive in a range of temperatures. For example, they have been observed occupying icy snowmelt and hot springs.

Unfortunately, not much is known about skiff beetles’ reproductive cycle. However, at least one species of this family lays a single large egg on a mat of algae.

Skiff beetles occur on every continent except Antarctica.

4.      Travertine Beetles

Travertine beetles, also known as Lutrochida, are a family of water beetles native to North America and common in springs and streams.

Their most distinguishing feature is their ovate bodies, roughly 0.15 to 0.23 inches in length. Travertine beetles are yellowish in color and have short antennae; their first two antennae are longer than the rest.

The larvae have elongated bodies measuring around 0.15 to 0.39 inches, with short but well-developed legs. Travertine beetle adults and larvae occur in fast-moving water and feed on wood and algae.

The Lutrochida family is known only from the New World and includes 12 species in a single genus, Lutrochus. However, upon review, it is likely the genus will be divided. This is because the genus is classified under Limnichidae and Dryopidae, but it has recently been put in its own family.

5.      Water-penny Beetles

Water-penny beetle is a general name used to describe water beetles belonging to the family Psephenidae. Approximately 260 known species belong to this family, but there are likely many more yet to be discovered.

They inherit their name from the round, flat appearance of their larvae. However, adult water-penny beetles look entirely different from their larvae. Adults are typically black or brown in color and measure 0.15 to 0.23 inches.

Their antennae are short and threadlike, and their bodies are slightly flattened. Larvae don’t all look alike; some slightly vary in appearance depending on the species. However, they all have a flat-round shape, with their heads and legs encompassed by their dorsal plates.

Where they do vary is their length, which ranges from 0.12 to 0.39 inches, and water penny beetles come in an array of colors like pale amber and dark brown.

These beetles are found on every continent except Antarctica.

Water penny beetles have an average lifespan of 21 to 24 months, and due to adults’ short time on this earth, researchers believe they might never feed at all. However, larvae are herbivores and eat algae and other microorganisms that live on freshwater rocks.

6.      Japanese Water Beetle

Japenese beetles, also known as Popillia japonica, are native to Japan and other Asian countries. However, they were introduced to the USA accidentally and have since flourished.

These water beetles are known for their copper-colored, iridescent elytra, measuring 0.6 in length and 0.4 inches in width. Their head and thorax are a greenish color, which makes them stand out, so they are easy to identify.

In America, the Japanese beetle is considered a pest; however, in Japan, it keeps a low profile and doesn’t cause much damage.

The adult Japanese beetle eats nearly 300 different plant species, including:

  • Birch trees
  • Grapes
  • Hops
  • Linden trees
  • Canna
  • Crape Myrtles

These beetles decimate the leaves of plants; once they are done with them, all that is left are the veins, no leaf material whatsoever. This gives the plants a skeletal appearance. In addition, they also feed on fruits.

7.      Predaceous Diving Beetles

Predaceous diving beetles are dynamic little creatures that are well adapted for aquatic life. They have a whopping 4,000 species in their family, making them an abundant and diverse species.

Over 550 species are distributed across North America, and they are members of the most prominent beetle family in the world, Dytiscidae, which in Greek means ‘able to dive.’

Predaceous diving beetles derive their name from adults and larvae’ ability to feed on anything they can find within their habitat. That includes animals like:

These unique beetles also have the ability to fly, and they can cover considerable distances in large numbers.

They stealthily crawl to the ground at surface level to fill their air sacs before taking flight. Then, when they return to the water, they dive in at a fast speed.

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About the Author

I am a 33-year-old creative and professional writer from South Africa. Wildlife is one of my greatest passions and led me to become the writer I am today. I was very blessed to work with an abundance of wildlife (mainly big cats) and captured my unique experiences in writing. But I wanted to take it further, and I ventured into the freelancing world. Now, I get to spend my days writing about animals; what could be better?

Water Beetle FAQs (Frequently Asked Questions) 

What is the role of the water beetle?

Water beetles play an essential role in the ecosystem through nutrient cycling, primary production, decomposition, and materials translocation.

What do water beetles eat?

They mainly eat decaying or dead aquatic plants, tadpoles, small fish, insects, and snails.

How big is a water beetle?

Water beetles are generally shiny and gray or dark brown in color. They are small beetles and only measure 1.5 inches in length.

What is the lifespan of a water beetle?

Water beetles do not live long; some only make it a few months. However, their average lifespan ranges from 2 to three years.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.

  1. Insect Identification, Available here: https://www.insectidentification.org/insect-description.php?identification=Water-Scavenger-Beetle
  2. Animal Corner, Available here: https://animalcorner.org/animals/water-beetle/
  3. Kidadl, Available here: https://kidadl.com/facts/animals/water-beetle-facts
  4. Wikipedia, Available here: https://en.wikipedia.org/wiki/Water_beetle

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