While I was doing a water change on the goldfish tub a few days ago, I realized I should probably clean the sponge in the filter, as I hadn’t properly done that since I took the goldies back inside. So I opened the filter, and – ew! Crawling around on the sponge were at least 25 squirmy insects, which I recognized as damselfly nymphs. The last thing you want to see in your aquarium.
Damselfly nymphs in the aquarium
Although these nymphs look a bit like dwarf shrimp from a distance, they are not nearly as peaceful – in fact, they are carnivorous and known to attack shrimp and even small fish.
The nymphs entered my filter because it was outside for a while and damselflies got the chance to lay eggs in there, but they can also get into your aquarium by hitching a ride on a bunch of plants in their egg stage. If it’s already too late and you find them in your aquarium, it’s a good idea to remove them as soon as possible; before they can do any harm to your stock.
Preventing these nymphs from ever getting in your tank is the best idea, though! You can do this by “quarantining” new plants for up to a week. A bleach dip with diluted bleach (1:8 to 1:10) and thorough rinsing with water after is also recommended sometimes, but I wouldn’t do this with expensive or sensitive plants.
Even though these nymphs didn’t actually enter the goldfish tub nor did they arrive on plants, this did remind me why I’m always so careful. Remember to not just quarantine fish, but also any plants you buy. All kinds of things, ranging from rather innocent snails to these carnivorous larvae, could be introduced in your tank if you don’t.