Damselfly nymph

Sep 09

written by Ulli Bauer

Scientific name:

Zygoptera

Picture:

Damselfly nymphs are often brownish to black or even green, their head is clearly set off from the body and their abdomen is oblong with long, narrow, leaf-shaped gilled appendages. They have three pairs of legs.
Length: up to 30 mm

Origins/distribution:

Almost globally in fresh water

Food:

Lurking predator, eats small crustaceans, water insects, mosquito larvae, …, which they catch with the help of their toothed lower lip normally folded under their head that shoots out when prey is near

Reproduction:

larval stage of the damselfly, cannot reproduce in the water
the damselfly female lays its eggs into the tissue of aquatic plants or onto suitable substrates on or shortly below the water surface

Locomotion:

Crawls, swims meanderingly

Introduction:

In most cases with waterplants or live food caught in nature

Diagnosis:

Damselfly nymphs are nocturnal, so if you have reason to believe that there is one (or more) of these predators present (dead shrimp with parts bitten off or mysteriously disappearing shrimp), just shine a flashlight into the dark aquarium and look closely. These animals are true masters of camouflage and very hard to find. Many times tankkeepers have found out they had damselfly nymphs in their tank because they found a metamorphosed damselfly under their tank lid.

Countermeasures:

Anything that eats damselfly nymphs also eats shrimp (and often likes the latter better). Anything that’s poisonous for damselfly nymphs is also poisonous for shrimp. The nymphs are dedicated predators and are not lured by bait.

Damselfly nymphs can thus only be removed by manually catching them one by one. As their egg clutches vary in size according to the species it is quite possible that there are more than just one or two in your tank, many more. For this task you’ll need lots of patience.

Please note: Damselflies are protected in many countries! So if you are absolutely sure that you introduced the nymphs with live food from a natural water body, please make sure you put them outside as soon as possible.

However, if damselfly nymphs or eggs have been introduced with aquatic plants possibly raised in tropical plant nurseries, things look quite different. In order not to introduce neozoans to nature, please do not release them, but euthanize with iced saltwater. For this, pour as much salt in warm water until nothing dissolves any more. Put into the freezer. The water will not freeze due to the salt, but attains the freezer’s temperature as low as -18 °C. This kills reliably and fast.