Profile of Diving Beetles: Monsters in Shrimp and Fish Tanks

Profile of Diving Beetles- Monsters in Shrimp and Fish Tanks

Diving beetles, members of the family Dytiscidae, are fascinating aquatic insects known for their predatory and carnivorous nature. These natural-born hunters possess unique adaptations that make them highly effective in capturing and consuming their prey even if it is bigger than them.

That is why their presence in an aquarium, particularly those housing small fish and shrimp, can and will lead to huge problems.

In this article, I will delve into the physical characteristics, dietary preferences, life cycle, and habitat requirements of Diving beetles and their larvae. I will also highlight the potential risks and considerations associated with keeping diving beetles in aquariums, particularly in contexts where they may jeopardize the well-being of small fish and shrimp populations.

Etymology of Dytiscidae

The family name “Dytiscidae” is derived from the Greek word “dytikos,” which means “able to swim” or “pertaining to diving.” This name aptly reflects the aquatic nature and swimming abilities of the beetles belonging to this family.

The name “Dytiscidae” was coined by the French entomologist Pierre André Latreille in 1802 when he established the family classification. Latreille is renowned for his significant contributions to the field of entomology and the establishment of modern insect taxonomy.

As for their common name “Diving beetles”, this name they got because of their exceptional ability to dive and swim in water.

Evolutionary History of Diving Beetles

Diving beetles originated during the Mesozoic Era (about 252.2 million years ago).

Over time, they have undergone diversification, resulting in the development of numerous species with varied body forms, sizes, and ecological preferences.

This evolutionary process has allowed Diving beetles to occupy various freshwater habitats worldwide and become successful aquatic predators.

Taxonomy of Diving Beetles

The exact number of species is subject to ongoing research because new species are continually being discovered and reported.

Currently, there were around 4,200 species of Diving beetles worldwide.

Distribution and Habitat of Diving Beetles

Diving beetles have a widespread distribution. Basically, these beetles can be found on every continent except Antarctica.

Water beetles usually inhabit stagnant bodies of water (such as lakes, marshes, ponds, or slow-moving rivers), preferring deeper ones with abundant vegetation and rich animal populations that can provide them with an ample food supply.

Description of Diving Beetles

The body structure of Diving beetles is well-adapted to their aquatic lifestyle and predatory behavior.

  • Body Shape: Diving beetles have an elongated, flattened, and hydrodynamic body shape, which allows them to move efficiently through water.
  • Size: The size of diving beetles can vary depending on the species. Some larger species can reach up to 1.5 inches (4 cm) in length.
  • Coloration: Diving beetles often have black or dark brown to dark green or bronze bodies. The coloration helps them blend into their aquatic environment.
  • Head: The head of a diving beetle is relatively large and well-developed. The eyes are usually prominent and provide excellent vision both above and below the water surface. They also have long, slender antennae, usually segmented, which they use for sensory purposes (detect vibrations in the water).
  • Wings: Diving beetles have two pairs of wings. When the beetles are swimming, the wings are kept folded against their bodies. They are capable of flight and use their wings to disperse and find new habitats.

The forewings are modified into hard, protective covers called elytra, which help protect the delicate hindwings and the body when the beetle is not flying. The elytra are often grooved or ridged, adding to the beetle’s streamlined appearance.

  • Legs: Diving beetles have 6 legs. The front and middle legs are used for capturing prey and maneuvering in their environment. The hind legs are modified into flattened, paddle-like structures known as oar-like legs or swimming legs. These legs are fringed with hairs or bristles that help propel the beetle through the water with ease.

With such perfect paddle-like legs, the beetle swims with such speed that it can compete with fish.

  • Abdomen: The abdomen of a diving beetle is elongated and often tapers towards the rear. It consists of several segments and houses important organs such as the digestive, reproductive, and respiratory systems.
  • Respiratory Structures. Diving beetles have a pair of spiracles, which are small openings located on the underside of the abdomen. The spiracles allow them to extract oxygen from the air, which they store beneath their elytra and use for respiration when submerged.
Profile of Diving Beetles- Monsters in Shrimp and Fish Tanks - Respiratory StructuresBefore diving beneath the water, diving beetles capture a bubble of air beneath their elytra. This air bubble acts as a hydrostatic apparatus and a temporary oxygen supply, allowing them to remain submerged underwater for 10 – 15 minutes.

After that, they extend their hind legs to break through the water’s surface tension, releasing trapped air and acquiring a fresh bubble for the next dive.

Life Cycle of Diving Beetles

The life cycle of Diving beetles consists of 4 distinct stages: egg, larva, pupa, and adult.

1. Egg Stage: After mating, female diving beetles lay their eggs on or near aquatic vegetation, submerged debris, or in the soil near the water’s edge.

Depending on the species and environmental conditions, the incubation period usually lasts from 7 – 30 days.

2. Larval Stage: Once the eggs hatch, the diving beetle larvae emerge. The larvae are aquatic and undergo development in the water.

Profile of Diving Beetles- Monsters in Shrimp and Fish Tanks - Diving Beetles LarvaeDiving beetle larvae are often referred to as “Water tigers” due to their fierce appearance and predatory nature.

They have coarsely segmented elongated bodies. The flat head has six small eyes on each side and a pair of unbelievably enormous jaws on each side. Like the adult beetle, the larva breathes atmospheric air by extending the posterior end of its body out of the water.

The character of the larva perfectly matches its appearance: its sole aspiration in life is to catch and devour as much prey as possible.

The larvae actively hunt and feed on small aquatic organisms, growing and molting several times as they go through various instar stages. The larval stage can last for several weeks to several months, depending on the species and environmental conditions.

3. Pupa Stage: When the larva reaches maturity, it emerges onto land, buries itself, and undergoes pupation.

During this stage, the larvae transform into their adult form within a protective case called a pupal chamber.

The pupal stage typically lasts for a few days to a couple of weeks.

4. Adult Stage: Once the metamorphosis is complete, the adult diving beetle emerges from the pupal chamber and rises to the water’s surface.

At this stage, they have fully developed wings and are capable of flight. Adult diving beetles are sexually mature and ready to reproduce.

Diving beetles are not considered social insects. They do not exhibit the complex social behaviors seen in some other insect groups, such as ants or bees. Instead, diving beetles are primarily solitary creatures, focusing on their individual survival and reproduction.

The lifespan of diving beetles can vary depending on the species and environmental conditions and generally ranges from 1 – 4 years.

Reproduction of Diving Beetles

Profile of Diving Beetles- Monsters in Shrimp and Fish Tanks matingThe mating behavior and reproductive strategies can vary slightly among different species of diving beetles, but the general process involves the following steps:

1. Courtship: In Diving beetles, courtship behaviors usually do not exist.

2. Copulation: In many Diving beetles, males have specialized grasping structures (suction cups) on their front legs used to attach to the back of females during mating. 

Interesting fact: Sometimes males can be so eager to mate with females, that females can even drown because males stay on top and have access to oxygen while females do not.

3. Fertilization. The male transfers sperm to the female through a reproductive organ called the aedeagus. The female stores the sperm for later fertilization.

4. Oviposition: After mating, the female diving beetle typically attaches them to submerged vegetation or deposits their eggs in the tissues of underwater plants by cutting them open with their ovipositor. You can notice small yellowish marks on the plant tissue.

On average, female diving beetles can lay anywhere from a few dozen to a few hundred eggs during a breeding season. The eggs are elongated and relatively large in size (up to 0.2 inches or 7 mm).

What Do Diving Beetles Eat?

Profile of Diving Beetles- Monsters in Shrimp and Fish Tanks - eating frogs, fish and newtsDiving beetles are carnivorous predators that primarily feed on a variety of live aquatic organisms such as:

  • small insects,
  • insect larvae (such as dragonfly nymphs, or even diving beetle larvae),
  • worms,
  • snails,
  • tadpoles,
  • small crustaceans (such as water louse, etc.),
  • small fish,
  • and even small amphibians (newts, frogs, etc.).

They have been known to exhibit some scavenging behavior, feeding on decaying organic matter or carrion. During times of food scarcity, they will also exhibit cannibalistic behavior. Larger beetles will prey upon smaller individuals.

Note: Of course, the specific food preferences of Diving beetles vary depending on the species and their size. In all species, they may consume a significant amount of prey relative to their body size.

These beetles are known for their voracious appetites and their ability to capture prey both on the water’s surface and underwater. They are opportunistic hunters, using their keen vision and excellent swimming abilities to track and catch their prey.

Diving beetles are active hunters. They usually exhibit an active predatory behavior by actively seeking out and pursuing their prey rather than waiting for it to come to them.

These beetles are highly skilled and agile predators in the aquatic environment.

Their ability to swim swiftly and change direction rapidly allows them to actively chase down and seize their prey with precision.

What Do Diving Beetles Larvae Eat?

Diving beetle larvae are carnivorous predators. They are known for their extremely aggressive feeding behavior as well.

Although they have also a broad diet and can consume a wide variety of prey, they prefer worms, leeches, tadpoles, and other animals that do not have strong exoskeletons.

This is because of their anatomical structure. Diving beetle larvae often have closed mouth openings and use channels in their large (sickle-like) mandibles to inject digestive enzymes into the prey. Enzymes quickly paralyze and kill the victim.

Therefore, during feeding, the larva doesn’t consume its prey but rather sucks the juices. Its sickle-shaped jaws act as a sucking apparatus, featuring a deep groove along the inner edge, which serves to channel the liquid food into the intestine.

Unlike their parent, Diving beetle larvae are passive hunters and rely on stealth. They have excellent vision and are sensitive to movement in the water.

When a Diving beetle larva detects prey, it will dash toward it to catch it with its large mandibles.

Is It Safe to Have Diving Beetles or Their Larvae in Shrimp or Fish Tanks?

Shrimp tank. No, by no means it is safe to have Diving beetles or their larvae in shrimp tanks. Period.

It will be EXTREMELY dangerous and stressful for the shrimp. Diving beetles are natural predators and will view shrimplets and even adult shrimp as potential prey.

These water monsters have strong jaws and can tear apart shrimp within seconds easily. Therefore, it is ABSOLUTELY NOT RECOMMENDED to keep Diving beetles and shrimp together in the same tank.

Fish tank. Diving beetle and their larvae may even attack fairly large fish. In nature, both adult beetles and larvae play a significant role in depleting the fish population by preying on various fish fry.

So, having them in a fish tank can also become counterproductive. Unless you have really large fish and do not breed them.

How Do Diving Beetles Get into Aquariums?

Diving beetles can get into an aquarium in 2 main ways:

  1. No lid: Diving beetles can fly really well. So, if your windows are not closed and your aquarium is not covered, they may simply fly into the tank from the surrounding environment.
  2. Aquatic Plants: Diving beetles eggs can hitchhike into your aquarium on aquatic plants. When adding new plants or decor to your tank, thoroughly inspect and quarantine them for any signs of parasites.

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How to Get Rid of Them in Aquarium?

Unfortunately, there are not many effective methods. Diving beetles and their larvae are pretty hardy animals and can tolerate almost any treatment.

  1. Manual Removal: Carefully observe the aquarium and manually remove the diving beetles using a fish net.
  2. Traps: Diving beetles like meat. Place a shallow dish with a light source near the water surface overnight. The beetles are drawn to the light and may gather in the dish, making it easier to remove them.
  3. Predatory fish: Introducing predatory fish that naturally feed on insects. However, these aquatic monsters are relatively well-protected here as well.

In case of danger, Diving beetles release a whitish liquid (resembling milk) from under their chest plate. This liquid has highly corrosive properties. As a result, many fish species do not find them palatable and avoid them.

Are Diving Beetles or Their Larvae Poisonous?

No, they are not poisonous.

Diving beetles are not aggressive toward humans and typically avoid contact unless they feel threatened. So, if you try to catch them, they may respond defensively by biting as a reflex action.

Due to their powerful mandibles, which are suited for piercing their prey’s exoskeletons, their bite is quite painful. It can cause localized swelling or itching.

In Conclusion

Diving beetles are primarily aquatic insects, spending most of their life in water. They are well-adapted to an aquatic lifestyle and are excellent swimmers.

Diving beetles and their larvae are innate ferocious predators. Hunting is the main activity in their life.

Their predatory instincts, coupled with their specialized anatomical features, enable them to pursue and capture a wide range of prey including shrimp, fry, small fish, and even snails.

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