Dragonflies and damselflies have been here for over 300 million years (even before the dinosaurs even existed!). About 3012 species of dragonflies only were known in 2010. They come in many shapes and sizes but they are all predatory. These are like the sharks of the insect world. They are extremely adaptable to survive in the sky and underwater. Everyone knows the colorful adult dragonflies. However, few people know that 95% of their life cycle they spend under water as dragonfly nymphs or naiads.
All dragonfly nymphs are fierce and voracious predators. They kill and eat any animal that they can catch including shrimp and fish of their size. Once dragonfly nymphs are in your aquarium they will start hunting non-stop until you deal with them. In some cases, they can even force to restart the aquarium.
I know that some shrimp breeders lost whole shrimp colonies because of these kill machines. So today I will tell everything you need to know about them.
|Life span||Up to 5-7 year (from the egg stage)|
|Size (adult damselfly )||vary between 2 cm to 8 cm (0.8 – 3.2 inches)|
|Size (damselfly nymph)||between 1.5 – 3 cm (0.6 – 1.2 inches)|
|Eggs||From hundreds to as many as 1500 eggs originally hatched|
Both species are voracious predators.
Why are they called Dragonflies?
It is possible that the earliest reference to the name is from Francis Bacon’s “Sylva Sylvarum: or a Natural Historie in Ten Centuries.” It was published in 1626, where he first used common name “Dragon-fly”. At a guess, Bacon had picked up on a common, folklore name in use at the time. Prior to this date (and since) many different vernacular names have been used. Some are Adder Bolt, Snake Doctor, Devil’s Riding Horse, Horse Stinger, and Devil’s Darning Needle.
The Life cycle of the Dragonfly Nymphs
Dragonflies and damselflies have three stages to their life.
Note: The length of each stage depends on the species of dragonfly.
- Adult stage.
After the final molt from nymph to adult, occurring in late spring or early summer in temperate regions and at any time of the year in tropical regions, most dragonfly species spend the next month fully maturing. Their gonads (sex organs) finish developing, their color becomes brighter with their final markings emerging and they disperse, sometimes hundreds of miles, from the pond or marsh where they developed.
Obviously, we are not very interested here in the adult stage.
- Egg stage.
Some damselflies and dragonflies females will settle on vegetation and insert eggs into stalks of the plants (endophytic eggs) and other material in or near the water. There are also dragonflies which usually fly across the water dipping the end of their abdomens into the water and releasing eggs. These eggs (exophytic eggs) are covered with a jelly-like substance and can stick to vegetation or the bottom of the pond. Depending on the species, a female can lay hundreds or thousands of eggs during her lifespan.
- Nymph stage.
When dragonflies hatch (~1mm size) they are called nymphs. Dragonfly nymphs are voracious predators that have no resemblance to their adult forms. They molt up to 12 – 17 times, depending on the species and can spend as long as 4-5 years as nymphs.
During the nymph stage, they are very elusive. The dragonfly nymphs can survive months in the aquarium without detection. In most cases, the first time people find out about them when the population of the shrimp (or small fish) colony starts decreasing without any obvious reason.
What is the Difference between Dragonfly and Damselfly Nymphs?
Damselfly nymphs have the elegant gill appendages trailing off the back of the abdomen. They are smaller and slender compared to dragonfly nymphs. Damselfly gills are located at the end of the abdomen. The head is wider than the thorax and the abdomen. Damselfly nymphs swim by undulating their bodies.
In addition, because of their size, they are not the best fish hunters, although dwarf shrimp will be in danger anyway. Eggs of a damselfly are cylindrical.
The size of the damselfly nymphs varies among the species from 15 mm to about 30 mm (about 0,5-1,2 inches).
Dragonfly nymphs are much more predatory and much bigger. They are a real threat to shrimp, small fish, snails, and fry. They also look very different from damselfly larvae. Dragonfly Nymphs are bulkier and stout. In addition, they have gills at the base of their rectum and breathe through their bottom. Dragonfly nymphs pull water into their rectums to breathe. When the hungry nymph is on the rampage this vent turns into hydro jet rapid contractions force water backward and propel the hunter forwards. Eggs of the dragonfly are round.
Their size can be from 15 mm to about 64 mm (nearly 2.5 inches).
How do I know that there are dragonfly or damselfly nymphs in the aquarium?
As I have already said, in most cases, the first time people find out about them when the population of the shrimp (or small fish) colony starts decreasing without any obvious reason. Thus, the first sign is the decreasing population of your aquarium inhabitants.
Another indication would be that both the small shrimps and fish are showing signs of stress. They are aware that there are predators in there with them.
Interesting fact: Did you know that dragonfly nymphs can also be stressed?
Biologists at the University of Toronto placed dragonfly nymphs and their predatory fish together in aquarium tanks. The two were separated so that although the dragonflies could see and smell their predators, the fish could not actually reach or eat the dragonflies. “What we found was unexpected — more of the dragonflies died when predators shared their habitat,” study researcher Locke Rowe, chairman of the Department of Ecology and Evolutionary Biology at the university, said in a statement. The survival rates were 2.5 to 4.3 times lower than those that had not been exposed to either stressor.
Hunting styles of dragonfly and damselfly nymphs
Their hunting methods can vary. Although some nymphs are active hunters. They use their camouflage and move slowly to be as inconspicuous. In addition, they can hunt even in complete darkness using their antennae and long legs to detect pressure waves.
However, most are sedentary, spending their time buried in mud or hiding in algae mats or other vegetation. The skimmers and green darners are mostly hide-and-ambush predators. Clubtails, however, are burrowers, and when placed into the aquarium with mud or sand bottom will spend much of the time hidden from sight. Obviously, this makes them harder to observe and more difficult to catch.
The nymphs catch their prey using a highly modified lower lips, known as a labium. Which they can thrust forward in less than 20 milliseconds to grab a passing shrimp, tadpole, or small fish. Nymphs contract their abdomen inside the water pressure builds, launching the jaw forwards. This lower lip is equipped with 2 pairs of needle-sharp pinchers and can be fully extended up to few centimeters. When they are fully grown, they are capable of catching and killing fish as big as they are.
Note: dragonfly or damselfly nymphs are carnivorous hunters from the start. According to the study, it was observed that nymph of 14 and 16mm size consume more than 100 mosquito larvae, between inter-molt stages. The predation rate of the nymph increases along with the size of the nymph. (*Laboratory studies on the predatory potential of dragon-fly nymphs on mosquito larvae. Article in The Journal of communicable diseases. July 2003)
Dragonfly Nymphs stage in the Shrimp tank
Depending on the species, dragonfly and damselfly nymphs molt between 9 and 17 times as they grow and develop. However, the climate (the temperature) plays a huge role here. In warmer climates, the nymph stage can last only a month or two, with the nymph growing very fast. Under colder temperatures, dragonfly nymphs may stay in the larval stage up to 4-5 years.
During the final nymph stage, it starts to develop the adult wings, although they remain tucked inside wing pads. The closer to adulthood the nymph is, the fuller the wing pads appear. When it is finally ready, the larva crawls out of the water for its last molt.
When it is near its final transformation an intricate system of cubes within its body will have to transition from getting oxygen from its gills to breathing air.
How can Dragonfly or Damselfly Nymphs Get in the Shrimp Tank?
They get into the aquarium in three main ways:
- Hitchhiking on plants (inside the stems of an aquatic plant or hidden inside the foliage of a plant).
- This predator might also be accidentally introduced along with mosquito larvae, daphnia or some other wild-caught live-food item.
- Because there was no lid on the tank and the dragonfly would have just dropped her eggs into the tank.
How to Prevent Them from Getting into the Shrimp Tank
There are simple rules, which can help you:
- Do not feed your shrimp and fish with the self-collected live food. It is not a good idea unless, for some weird reasons, you want to risk adding parasites and predators in your aquarium. At least, use great caution when collecting live food items such as daphnia or mosquito larvae from a naturally occurring body water.
- Quarantine any new plants. If insects laid their eggs on the plants, then you can unwillingly get them into the aquarium. Carefully inspect everything.
- Close the aquarium or put fine netting over your aquarium if there is a chance of getting parasites, in the place you live in.
The abilities of nymphs to survive without food for many days and weeks in addition to their abilities to hide makes it very hard to prevent them from getting into our aquariums.
How to Treat Dragonfly or Damselfly Nymphs
Well, I tried my best to get all the methods that can kill these monsters. Unfortunately, they are very hardy! Almost everything that can kill them will also kill shrimp and fish.
That is why some (most) of these methods cannot be used in shrimp or fish aquariums. Nonetheless, I will describe them anyway. Some shrimp and fish breeders say that this is the war which you cannot win (at least you cannot be 100% sure). Thus they advise to restart the tank and wipe out everything there.
If you do have some working methods to fight off these monsters, please, share them with us.
Manual removal and siphoning the tank
The best way to kill them is to grab dragonfly or damselfly nymphs with the net and remove them as you see them. You can also do a gravel vacuum and suck them out with a syphon. Keep monitoring for any new hatch and remove as you see them again.
Unfortunately, you will never know how many of them are already in the aquarium. They are masters of disguise. It is hard to spot them. They will usually just remain still. That is why you need to shake/agitate the plants with a net or something.
Note: Unless you treat the plants beforehand, there is always a chance that the plants are still “infected” with the eggs.
Most newly acquired plants you can dip in a saltwater solution for 20-30 seconds to kill/remove nymphs (1 cup of salt to 1 gallon / 3.8 liters of water).
Tip: A safer and more gentle alternative may be to let the plants sit in a covered container with no water. Many plants can survive outside of the water for extended periods as long as the air is humid. However, the dragonflies need water to breathe and will move to the base of the plant and then the container itself in search of water. Unfortunately, it will not work against eggs.
Chitin Inhibitor Medicine
You can treat the tank with chemicals like Chitin inhibitor. It prevents the dragonfly and damselfly nymphs from being able to molt properly and then they die.
Regrettably, all your dwarf shrimp will die as well. Unacceptable.
If you do not have shrimp and snails in the tank. It will wipe out every single nymph.
There was a study about “Differential Toxicity to Cd, Pb, and Cu in Dragonfly Larvae” (Archives of Environmental Contamination and Toxicology 56(1):77-84 · April 2008)
According to the results, “Larvae were tolerant of high concentrations of cadmium and lead, as no significant decrease in survival was observed at exposures as high as 0.893 and 2.232 mM, respectively. In contrast, larvae were more sensitive to copper exposure, demonstrating significantly decreased survival to exposures as low as 2.360 μm”.
Now, let’s convert 2.360 μm to mL. Correct me if I am wrong.
2.360 μm multiple with the Molecular weight of CuSO4 (159-249) and divid the resulted number /1000
2.360*159 (to 249)/1000 = from 0,375mL to 0,587 mL
Note: In one of my articles I refer to CuSO4 (Copper sulphate) as the treatment against Vorticella. The dangerous level of copper for dwarf shrimps starts from 0.03 mg per liter.
According to another study “Copper intoxication in tropical freshwater prawn” (International Journal of Engineering and Innovative Technology. Volume 3, Issue 5, November, 2013). Survival of prawns exposed to more than 0.20 mgL of Cu2+ was significantly reduced.
In any case, dragonfly and damselfly nymphs are way tougher than shrimp or fish. The copper concentration should be high enough.
Carbon Dioxide (CO2) Overdose
If there are no inhabitants in the tank, add CO2 with heavily overdose to decrease the level of oxygen in the tank.
Note: A CO2 content of 30 parts per million (ppm) or milligrams per liter (mg/l) is safe for most fish and inverts. 200-500 ppm is the range of toxicity for aquatic plants.
Snail-killing potions are often recommended as good ways to kill invertebrates attached to plants (during disinfection and/or quarantine). Used as a dip for 10-20 minutes they will remove snails from store-bought plants, and usually remove Hydra too.
I read on the Internet forum that high-temperature methods can also kill Dragonfly or Damselfly Nymphs. In order to do so, you need to set the temperature in your aquarium to 83 degrees F (~28,5C) constant for a few days.
I did my research about it and I found that there was also a study about thermal tolerance of dragonfly nymphs. They tested several types of Dragonfly Nymphs. Unfortunately, the results show that they have great resistance to high temperatures. Higher temperatures will allow body processes to happen faster. High temperatures will thus allow an animal to have the ability to metabolize faster, but only to a certain degree, before the heat kills them at the critical thermal maximum.
Critical thermal maximum is the temperature at which dragonfly nymphs are unable to adaptively respond to stimulation. They are disoriented and lack coordinated locomotory behavior. In this state, they cannot escape from conditions which, if continued, will lead to death.
Lethal temperature is the temperature at which all body movements cease because of death.
Thermal Tolerance of Dragonfly Nymphs. II. Comparison of Nymphs from Control and Thermally Altered Environments. Physiological Zoology. C. T. Garten, Jr. and J. B. Gentry Vol. 49, No. 2 (Apr., 1976), pp. 206-213 (8 pages)
As we can see the result of the study is different from the results of the hobby-aquarist. You need to set the temperature in your aquarium to 38 – 43 degree C (~100-109 F) to get at least critical thermal maximum.
In any case, unless you have Sulawesi shrimp even 83F (~28,5C) will be very dangerous for your neocaridina and caridina shrimp.
Sudden Drop of Water Temperature
This is another method from one of the shrimp breeders. You need to do a 50 % water change with a sudden drop in water temperature (~5-7 C). The sudden drop in water temperature can cause the shrimps to feel stressed (pale, motionless or going crazy swimming at the top of the water).
Nonetheless, it will also stress damselfly or dragonfly nymphs. They will get out of their hiding places and you can catch them.
Do Dragonfly Nymphs have enemies in the shrimp aquarium?
Well, no. They do not have enemies in the shrimp aquarium.
Of course, any big adult fish like Golden fish, Betta etc. will eat them gladly. As I mention in my article about “Сherry Shrimp in a Community Tank. Tips to Make it Successful” some people manage to keep shrimp with big fish. But this is an exception.
Other archenemies of the Dragonfly Nymphs are Waterbugs. They will deal with nymphs as well. Unfortunately, if they can overpower the dragonfly nymphs, any shrimp will be a piece of cake for them.
Eventually, as we can see, nymphs will rule in shrimp tank unconditionally.
Do Dragonfly Nymphs Bite or Sting?
They do not sting (there is no poison). They can only bite the prey.
Dragonfly nymphs are born hunting machines. They are well-armored, patient, tough, quick with strong grasping forelimbs. All in all, they are really formidable little aquatic monsters and they stay that way for life. Basically, they do not need anything but to hunt and kill in our tanks.
It looks like they eat anything that they can catch, any dwarf shrimp, snails, small fish, little frogs, tadpoles, baby turtles, worms, and even other dragonfly nymphs are all on the menu. And what is most dangerous about them is that they can live for years!
|Read also my article “Understanding Dwarf Shrimp Diseases and Parasites”.|