Why do diving beetles sometimes land on cars?

Shiny dark paint reflects light like water

How does a water tiger eat its food?

Digests it outside its body, then sips it

Where do diving beetle eggs usually go?

Inside the stems of water plants

Predaceous Diving Beetles

Dytiscidae

Predaceous diving beetles (family Dytiscidae) are a worldwide family of more than 4,000 water beetles that hunt in ponds, lakes, streams and even underground waters. Adults carry a store of air under their hard wing cases and row with flattened, hair-fringed hind legs, while their long, thin larvae, nicknamed “water tigers”, ambush prey with hollow, sickle-shaped jaws. The great diving beetle (Dytiscus marginalis) of Europe and northern Asia, 27–35 mm long, is one of the best known.

Also known as Diving beetles, Predacious diving beetles, Predaceous water beetles

Diving beetle abilities

12.9 cm/s top forward speed in one stroke
Diving beetles row with their two flat, hairy hind legs, pushing both at the same time. They can even swim backwards without turning round.
- In high-speed films of Cybister bengalensis, a 36 mm beetle, forward speed peaked at 12.9 cm/s during a stroke and averaged 8.74 cm/s.
- Swimming backwards, probably to escape danger, it went from 0 to 27.3 cm/s in just 50 milliseconds.
- The legs push hard on the power stroke and meet little resistance on the way back. Computer flow models gave a forward efficiency of 0.47.
Cybister bengalensis swimming speeds
Backwards escape burst27.3 cm/s
Forward, fastest moment12.9 cm/s
Forward, average8.74 cm/s
Measured with high-speed cameras at 1,000 frames per second.
Sources [7, 8, 13]
minutes–24 h per dive, depending on species
Before diving, the beetle tops up the air store under its wing cases by touching the surface with the tip of its abdomen. Then it can stay under for minutes or hours.
- Dives last from a few minutes to 24 hours, depending on the species, how active the beetle is and the water temperature.
- A small bubble at the tail tip acts as a physical gill, pulling a little extra oxygen in from the water.
- One stream-living species, Deronectes aubei, survived more than 6 weeks without surfacing, and some beetles in underground waters in Australia breathe through their skin.
Sources [2, 5, 6, 14]
2 pairs of wings: hard cases and flight wings
Under the hard wing cases sit two things a swimmer needs: a pocket of air to breathe and a pair of folded flight wings for leaving the pond.
- The wing cases are the beetle’s front wings, hardened into a shell. They seal in the air store.
- The thin back wings fold away underneath when the beetle swims and open out when it flies.
- The air store is refilled at the surface through the gap at the tip of the abdomen.
Sources [1, 2, 5]
99 kinds of water insect studied in flight
Diving beetles climb out, open their wings and fly to new ponds. They find water by its shiny, polarised glare, which can fool them into landing on cars.
- A study of 99 kinds of flying water insects (78 of them beetles) found that they fly mainly in mid-morning, around noon or at nightfall, depending on the species.
- The great diving beetle is said to fly mostly at night.
- Shiny red and black car roofs reflect light like a pond does, so water beetles sometimes land on them by mistake.
Sources [1, 10, 15]
3 large cups per front foot in Acilius males
Male diving beetles have front feet like suction pads to hold on to a female under water. Females in many species have grooved wing cases that make them hard to grip.
- Charles Darwin used male and female diving beetles as an example in his work on differences between the sexes.
- A 2007 study found that each new female surface that weakens the grip is matched by changes in the males’ suction cups: an evolutionary tug of war.
- Some species have two kinds of female, one rough and one smooth. Tests showed the cups stick less well to the rough kind.
Sources [3, 4, 9, 16]
≈50% of the sunburst beetle’s defence volatiles are one steroid
When grabbed, diving beetles ooze a milky defence fluid from glands behind the head, and another secretion from glands at the tail tip.
- The sunburst diving beetle’s milky fluid is mostly steroids: one, mirasorvone, makes up about 50% of the volatile chemicals and cybisterone about 20%.
- Mirasorvone was the first steroid of its kind found in any insect.
- Scientists think the steroids can make a fish spit the beetle back out. Glands at the tail tip make a second, different secretion.
Sources [2, 17, 18]
15 s to catch a moving tadpole
The larva grabs prey with hollow, curved jaws, sends digestive juice in through them and then sips the softened food back out.
- Each jaw has a fine channel that opens near the tip. The larva digests its meal outside its body, then drinks it.
- Movement switches on the attack: larvae caught swimming tadpoles in about 15 seconds but took about 120 seconds over still ones.
- Larvae of the Japanese Dytiscus sharpi prefer to hold a tadpole by its belly, the most nourishing part.
Sources [2, 19, 20]
below 8 °C winter cold needed to ripen eggs (D. sharpi)
Many diving beetles stay active in cold water all winter, even under the ice. Some species actually need the cold to breed.
- In Nova Scotia, Canada, the diving beetle Laccophilus maculosus stays active all year, including in ice-covered ponds (2026 study, not yet peer reviewed).
- Dytiscus sharpi in Japan starts mating when the water drops below 20 °C, mostly in November and December.
- Its females only ripen their eggs after a winter below 8 °C, then lay them in spring.
Temperature switches in Dytiscus sharpi
Mating starts below20 °C
Eggs ripen after winter below8 °C
Lab and field study in Japan (Inoda et al. 2007).
Sources [21, 22]

Tap a pin on the model or a part below.

27–35 mm great diving beetle length
- The hard front wings, called elytra, close over the back like a smooth, streamlined shell. Head, thorax and abdomen fit together into one oval.
- In the great diving beetle, a yellow rim runs around the shield behind the head (the pronotum) and along the wing cases.
- Males have smooth wing cases. In many species the females have grooves or a rough surface instead, which makes it harder for a male’s suction cups to hold on.
Sources [1, 2, 3, 4]
up to 24 h on one air store, depending on species
- Between the wing cases and the abdomen is a space filled with air. The beetle breathes from it through small holes in its sides called spiracles.
- It refills the store at the surface, then dives again. Depending on the species, how active it is and how warm the water is, a dive lasts from a few minutes to 24 hours.
- The see-through flight wings are folded underneath too, ready for flying to a new pond.
Sources [1, 2, 5]
8× longest dive extension a bubble gill could give, in theory
- A small bubble is often pushed out from under the wing cases and held at the tip of the abdomen by water-repelling hairs.
- The bubble works as a “physical gill”: as the beetle uses up its oxygen, more oxygen seeps in from the water.
- Models say this could make a dive more than 8 times longer, but real insects come up for fresh air long before the bubble runs out.
Sources [2, 6]
≈80% of body length (Cybister)
- The hind legs are long, flat and fringed with stiff hairs, so they work like a pair of oars.
- Big diving beetles stroke both hind legs at the same time, like a rower, rather than one after the other.
- In the Asian diving beetle Cybister bengalensis, each hind leg is about 80% as long as the whole body.
Sources [7, 8]
3 large suction cups on each front foot (Acilius males)
- In males of many large diving beetles, the front feet are widened into round pads covered in tiny suction cups. In the great diving beetle the middle feet have some too.
- Males use them to hold on to a female’s back during mating, under water.
- In the genus Acilius, each male front foot has 3 large cups and many tiny ones. Round, later-evolved sucker hairs grip better than older spatula-shaped ones.
Sources [1, 3, 9]
- Flying diving beetles find water by looking for shiny surfaces that reflect light in a special, flat-lying (horizontally polarised) way, as ponds do.
- That is why they sometimes land on shiny red or black cars, which reflect light in the same way. Yellow and white cars do not fool them.
- The larvae of the sunburst diving beetle have some of the strangest eyes known: their main eyes have bifocal lenses with two retinas, a little like reading glasses.
Sources [10, 11, 12]
up to 11 segments
- Diving beetle antennae are long and thread-like, usually longer than the head is wide, with up to 11 segments.
- This is a quick way to tell them from water scavenger beetles and whirligig beetles, whose antennae end in a club.
- They are smooth and bare: scientists call them glabrous.
Sources [2]
- Adults have strong jaws (mandibles). They bite off and swallow small pieces of their food.
- They eat live animals and also clean up dead ones, so they are both hunters and scavengers of the pond.
- If picked up, a big diving beetle can give a sharp nip. Watch it in the water instead of handling it.
Sources [2]

Real diving beetles

Photos from Wikimedia Commons. Some of them can repaint the 3D model.

A great diving beetle in Finland: note the yellow rimPhoto: Thintkk, CC BY-SA 4.0
Female great diving beetleSame colours as the male, but the wing cases usually have long grooves, and the front feet are plain.Grooves make her harder to grip. In some species, such as Dytiscus lapponicus, some females are smooth instead.A female great diving beetle, with grooved wing cases. Photo: Bram Koese, CC BY-SA 4.0
Larva (“water tiger”)Long and thin, with a flat head, big curved jaws and a breathing tube at the tail tip that it pokes up through the surface.Up to 60 mm in the great diving beetle, longer than the adultA water tiger: great diving beetle larva in Berlin. Photo: Leonhard Lenz, CC BY-SA 4.0
Larva (“water tiger”)Long and thin, with a flat head, big curved jaws and a breathing tube at the tail tip that it pokes up through the surface.Up to 60 mm in the great diving beetle, longer than the adultHanging from the surface by its breathing tube, waiting for prey. Photo: Hulcr, CC BY-SA 4.0
Sunburst diving beetleThermonectus marmoratus: shiny black, scattered with bright yellow spots.Famous for its milky steroid defence and its larvae’s bifocal eyesSunburst diving beetle at Cincinnati Zoo. Photo: Ltshears, CC BY-SA 3.0
Sunburst diving beetleThermonectus marmoratus: shiny black, scattered with bright yellow spots.Famous for its milky steroid defence and its larvae’s bifocal eyesSunburst diving beetle photographed in Mexico. Photo: Juan Carlos Fonseca Mata, CC BY-SA 4.0
A great diving beetle in southern FrancePhoto: Bernard DUPONT, CC BY-SA 2.0
A great diving beetle near Begunitsy, RussiaPhoto: Nikolay Bulykin (Красный), CC BY-SA 4.0
Dytiscus latissimus pair: male on the right, female on the leftPhoto: Ikaruga1127, CC BY-SA 4.0

Diving beetles by the numbers

Measured by scientists in ponds and labs, from the tiniest species to the biggest.

Species: 4,200+; described worldwide, in almost every kind of fresh water; water beetles of all families add up to more than 13,000⁠[23, 2, 24]
Great diving beetle: 27–35 mm; adult length of Dytiscus marginalis⁠[1]
Water tiger: up to 60 mm; a fully grown great diving beetle larva, longer than the adult⁠[1]; Larva (max)60 mmAdult (max)35 mm
Biggest in Europe: 44 mm; Dytiscus latissimus, a protected species⁠[25, 1]; D. latissimus44 mmGreat diving beetle (max)35 mm
Smallest: ≈0.9 mm; Limbodessus atypicali, from underground waters in Australia⁠[2]
Top forward speed: 12.9 cm/s; peak of one stroke, Cybister bengalensis⁠[8]; Backwards burst27.3 cm/sForwards peak12.9 cm/s
Escape burst: 0–27.3 cm/s; swimming backwards, in 50 milliseconds⁠[8]
Time under water: minutes–24 h; per air store; one stream species lasted over 6 weeks⁠[5]
Hind-leg length: ≈80%; of body length in Cybister bengalensis⁠[8]
Rowing efficiency: 0.47; forwards (0.30 backwards), from computer flow models⁠[13]

Diving beetle myths and facts

Tap Myth or Fact for each claim, then check the answer.

0 of 8 answered

“Diving beetles breathe under water with gills, like fish.”
“Some diving beetles can stay under water for a whole day.”
“Diving beetles can fly.”
“Diving beetles sometimes mistake cars for ponds.”
“Water tigers chew up their food and swallow it in chunks.”
“Diving beetles survive being frozen solid in the ice.”
“All diving beetles are big.”
“Diving beetles eat mosquito larvae.”

Diving beetle records

Superlatives and record holders, each checked against its source.

Largest diving beetle
≈4.75 cm
Megadytes ducalis (Brazil)
known only from 11 museum specimens collected in the 1800s, and listed as Extinct⁠[28, 2, 29]
Biggest in Europe
44 mm
Dytiscus latissimus
one of the largest diving beetles in the world, and protected across the EU⁠[25]
Smallest
≈0.9 mm
Limbodessus atypicali (Australia)
lives in underground waters (aquifers)⁠[2]
Longest time submerged
6+ weeks
Deronectes aubei
a stream beetle that takes oxygen from the water through special hairs⁠[5]
Fastest getaway
0–27.3 cm/s
Cybister bengalensis
swimming backwards in 50 milliseconds⁠[8]
Bifocal eyes
1st
Sunburst diving beetle larva
first living animal shown to have truly bifocal lenses (before, only suggested for some trilobites)⁠[11]

The life of a diving beetle

From an egg hidden in a plant stem to a flying adult, with a stop on dry land in between.

Spring
Eggs in a stem
Females of Dytiscus and Cybister lay their eggs inside the stems of water plants, below the surface. Cybister females bite a hole in the stem first.⁠[30]
Hatching
Out of the stem
Each tiny larva has to wriggle out through a crack or hole in the stem and swim up to the surface to take its first breath.⁠[30]
Weeks of growing
Water tiger
The larva hunts tadpoles, insect larvae and other small animals, breathing through a tube at its tail tip. It sheds its skin as it grows.⁠[19, 2, 26, 12]
Fully grown
Up onto the bank
The big larva crawls out of the water and buries itself in mud on the bank. There it changes into a pupa.⁠[2]
Adult
Back to the water
The new adult returns to the pond. Great diving beetles grow to 27–35 mm.⁠[2, 1]
Any time
Flying to new ponds
Adults can fly off to find new water, often at certain times of day such as mid-morning or nightfall.⁠[15]
Autumn and winter
Cold-water breeding
Some species mate in late autumn and stay active under the ice. Dytiscus sharpi needs a cold winter before its eggs ripen.⁠[22, 21]
Years
A long life for a beetle
Some species live for several years as adults.⁠[2]

Diving beetle vs water scavenger beetle vs whirligig beetle

Three kinds of water beetle you might spot in the same pond, and how to tell them apart.

Predaceous diving beetle vs water scavenger beetle vs whirligig beetle
	Diving beetle	Water scavenger beetle	Whirligig beetle
Family⁠[2, 31, 24]	Dytiscidae	Hydrophilidae	Gyrinidae
Antennae⁠[2]	Long and thread-like	Short, ending in a club	Short, ending in a club
Where it swims⁠[2, 31]	Dives and swims under water	—	Whirls about on the water surface
Eyes⁠[31]	Not split	Not split	Each eye split into an upper half for air and a lower half for water
Underside⁠[2]	No keel between the legs	Many have a keel-like ridge between the legs	—
Swimming legs⁠[8]	Hind legs row together like oars	—	—

A dash means we did not find a source we trust for that cell.

Are diving beetles endangered?

Most diving beetles have never been assessed, and many are common. But some of the biggest are rare and protected, and one may already be extinct.

IUCN Red List

Varies by species

Trend unknown

Europe’s biggest diving beetle, Dytiscus latissimus, is Vulnerable on the IUCN Red List and has declined fast since the 1960s.⁠[32, 25, 33]

IUCN Red List, species by species

Threats

Drained and polluted wetlands
Draining lakes and farmland, and fertilisers and pesticides washing into the water, are thought to be behind the decline of Dytiscus latissimus.⁠[25]
Towns and climate change
Urban growth, deforestation, climate change and alien species are also on the list of suspected causes.⁠[25]
Fish in ponds
Fish are one of the main limits on where diving beetles live: they eat the larvae and compete for food.⁠[2, 34]
Over-collecting
In Japan, Dytiscus sharpi became one of the country’s most critically endangered insects through over-collecting and habitat loss.⁠[35]

What’s helping

Protected by lawAnnex II
Dytiscus latissimus and Graphoderus bilineatus are the two diving beetles listed in Annex II of the EU Habitats Directive. D. latissimus is also protected by the Bern Convention.⁠[25, 36]
Counting beetles
Scientists in Germany and Latvia tested trap-and-recapture methods to estimate how many Dytiscus latissimus live in a lake for the first time.⁠[25]
Searching for a lost giant
Ten forgotten museum specimens gave the first exact locality for Megadytes ducalis in Bahia, Brazil, so scientists can now go and look for it alive.⁠[28]
Wildlife ponds
Fish-free ponds with plenty of water plants are likely to suit them best, since fish eat the larvae and females lay eggs in plant stems. Diving beetles are also used as indicators of healthy ponds.⁠[2, 30, 34]

Diving beetles with their own status

Dytiscus latissimusVulnerable
Europe’s largest diving beetle, 44 mm long, now rare across its range.⁠[32, 25]
Graphoderus bilineatusVulnerable
The other diving beetle on Annex II of the EU Habitats Directive.⁠[36, 25]
Megadytes ducalisExtinct
The world’s largest diving beetle, from Brazil, known only from old museum specimens.⁠[29, 28]

Diving beetle quiz

Twelve questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

Where does an adult diving beetle keep its air?

Predaceous Diving Beetles field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

These beetles are fierce hunters, eating many small creatures that live in freshwater!

Primary Foods

insect larvae
tadpoles
small fish
aquatic worms
snails
Foraging Method: Pursuit

Age differences: Larvae and adults are both predatory, consuming similar but size-appropriate prey.

Ecological connections

great pond snailHunts
Adults and larvae prey on these common freshwater snails.
common frogHunts
Beetles readily consume tadpoles of this widespread frog species.
mallard duckEaten by
Diving beetles can be a food source for aquatic birds.
common house mosquitoHunts
Diving beetles eat mosquito larvae, but scientists are still testing whether they keep mosquito numbers down.

Safety

Danger 1/5 · Very low

Big diving beetles have strong jaws and can give a sharp nip if picked up, and they ooze a defence fluid when grabbed. Don't touch them: watch from the water's edge, and tell an adult if you get nipped.

Traits

Collections

Insects

Classification

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Dytiscidae

Also known as

Diving beetles · Predacious diving beetles · Predaceous water beetles · Dytiscids · Water tigers (the larvae)

Sources for these diving beetle facts

36 studies and references · checked Oct 16, 2026

Frequently Asked Questions

How to identify Predaceous Diving Beetles?

Look for hard wing covers meeting in a line down the back, then compare the antennae, body shape, legs and markings. Metallic colors shift a lot with lighting. Beetle Identifier: upload a photo and compare the visible details.

What is Predaceous Diving Beetles's wingspan?

5-80 mm

How big is Predaceous Diving Beetles?

0.9-47.5 mm

How long does Predaceous Diving Beetles live?

365-730 days

What does Predaceous Diving Beetles eat?

These beetles are fierce hunters, eating many small creatures that live in freshwater!

Where is Predaceous Diving Beetles usually found?

Wetlands

How does Predaceous Diving Beetles hunt?

Pursuit

How many legs does Predaceous Diving Beetles have?

Do diving beetles bite?

They can. Big diving beetles have strong jaws and may give a sharp nip if picked up, and they also ooze a defence fluid. Watch them in the water instead of handling them, and tell an adult if you get nipped.

How do diving beetles breathe underwater?

They carry air. Adults keep a store of air under their wing cases and refill it at the surface, tail first. A small bubble at the tail tip also draws a little oxygen from the water, like a simple gill. Larvae breathe through a tube at their tail tip.

How long can a diving beetle stay underwater?

From a few minutes to about 24 hours on one air store, depending on the species, how active it is and how warm the water is. A few stream and underground species hardly need to surface at all.

Can diving beetles fly?

Yes. They have folded flight wings under their wing cases and fly to new ponds, usually at set times such as mid-morning, around noon or at nightfall. They spot water by its shine, and sometimes land on shiny cars by mistake.

Why are diving beetle larvae called water tigers?

Because they are fierce hunters. A larva grabs prey with its hollow, curved jaws, sends digestive juice into it and then sips up the softened food. It attacks things that move, such as tadpoles and insect larvae.

What do diving beetles eat?

Small water animals such as insect larvae (including mosquito larvae), tadpoles and small fish. Adults also eat dead animals, which helps keep ponds clean.

How big do diving beetles get?

Most are 1–2.5 cm long. The great diving beetle reaches 27–35 mm, Europe’s biggest, Dytiscus latissimus, about 44 mm, and the smallest known species is about 0.9 mm.

Are diving beetles endangered?

Most species are common or have never been assessed. But Dytiscus latissimus and Graphoderus bilineatus are Vulnerable and protected in the EU, and Brazil’s giant Megadytes ducalis is listed as Extinct.

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