• You are viewing the forum as a Guest, please login (you can use your Facebook, Twitter, Google or Microsoft account to login) or register using this link: Log in or Sign Up

Bugs you might encounter in your aquarium


21 Feb 2008
Source: http://www.aquaticquotient.com/
Creator: marle (as given permission to post here)


Copepods, Cyclops


Size: 0,1 - 0,2 cm, 0.04 - 0.1 inches

Copepods are small and funny looking one eyed crustaceans. They usually move around the tank glass and other surfaces, usually with one short leap at a time. Harmless, cute, there's lots of different coloured species. Females carry 2 egg pouches on their tail.

Control - Complete eradication is all but impossible. Proper aquarium maintenance and filtration will keep their numbers down enough to be unapparent. Providing a good current, even without filtration, will also keep the Cyclops in check.

Notes - Cyclops are generally harmless to all but the tiniest of fish fry. (Guppy and Cichlid fry need not worry.) In fact, Cyclops are an excellent "first food" for those young fish capable of catching them and consuming them.

As long as the tank is well maintained, Cyclops pose no danger.

Water Fleas, Daphnia


Size: 0,1 - 0,5 cm, 0.04 - 1/4 inches

Water fleas are usually used as fish food. They are tiny crustaceans and are easily recognized of their jerky vertical "swimming". They are completely harmless and really interesting creatures. I call them fat, sad reindeers (well, they look like it ).

Seed Shrimp, Ostracoda


Size: 0,1 - 0,2 cm, 0.04 - 0.1 inches

Seed shrimp are tiny seed shaped crustaceans. They are usually a bit bigger than Copepods. They move in a same fashion as Copepods, eating all kinds of nice things from the glass/plant/etc. surfaces and you can see them walking inside the substrate too. Sometimes they swim in open water looking like drunken bees. Here's a really young CRS baby looking at a seed shrimp. Really cute, harmless.

Control - Complete eradication is often unsuccessful, except for larger species, which seem more fragile. Regular aquarium maintenance and proper filtration usually keep the populations down to unapparent levels.

Because of their structure, Ostracods are extremely resilient against toxins. By closing the two shells, they can survive extended amounts of time in the presence of medications and pesticides. Even if they die, the shells serve to protect the unborn young until conditions are right again.

Freshwater Limpet - Acroloxus lacustris


Size: 0,1 - 0,8 cm ; 0.04 - 0.3 inches

Since freshwater limpets, Acroloxus lacustris, are so small and also move really slowly, it might be hard to identify them as snails. They are small and can't do much damage to plants, but since they are small, it's impossible to find and remove eggs and the baby snails. Harmless.

Something that looks a bit similar are Nerite eggs. They are singular, white, hard, round or oval shaped and about 1 - 2 mm in diameter.



Size: 2 - 5 cm, 3/4 - 2 inches

Red, yummy worms (used as fish food too) which live inside the substrate. If disturbed and dig up, they will form a ball, if left alone, they will gather pieces of sand/gravel around their body forming a sort of tube where they live in and they'll stick their head out of the substrate looking like red hairgrass. If there's lots of them, the substrate is too dirty and might be good idea to do something about it. Only a few Tubifex in the substrate isn't anything to worry about though. They are harmless.

Control - Only manual removal or being eaten by a fish can be recommended.

Notes - Unless deliberately added to an aquarium, large Annelids such as earthworms are rarely found in aquaria. Aquatic species can survive for quite some time in the gravel. Terrestrial species usually die within a day. Even a single larger dead worm can cause severe disruption to the water quality of the tank. Unless eaten, they should be immediately removed before they die or burrow into the ground. Their use as a fish food is acceptable as long the worms do not manage to escape into the substrate.

Size: 0,1 - 0,3 cm, max. 0.1 inches

Nematodes are small, thin, white/transparent free-living roundworms and the "swim" moving themselves in a wave like pattern (well, forming an S shape). If disturbed, they will swim around wriggling briskly. You can find them from the substrate and they are the ones that might appear from the filter when you turn it on. These ones are harmless, but as with any other "pest", if there's too many of them, you are either overfeeding or just not keeping the tank clean enough of debris, decaying plant matter.

Control - Proper tank maintenance (water changes, vacuuming the substrate, avoid excessive feeding) will keep the numbers down to unnoticeable levels. Copper treatments are effective, but should be used with caution. Nematodes are eagerly eaten by small fry and shrimp.

Notes - Most often, when an aquarist sees a Nematode, it is a simple scavenger, and of no harm to fish or plants. However, parasitic species exist. The general rule is if the fish and plants appear healthy, the worms are harmless.

Planaria, flatworms


Size: 0,3 - 1 cm, 0.1 - 3/8 inches

Non-parasitic flatworms. Crossed-eyed grossness, just pure yucky! The only small creature I dislike (I get shivers down my spine even thinking about them). If you split it, it will regenerate and you will end up having 2 planaria. There seems to be several different colours in the common ones found in aquariums, transparent, white, brown and red. There's actually nothing really horrible about them, but they can bother small shrimp and snails and might eat fish/snail eggs.

They love shrimp pellets, pieces of meat, dead fish/shrimp and they will also eat small live creatures if they can catch them. They move on the surfaces, even under the water surface and are most active by night. If disturbed, they will retract themselves (shorter and wider), let go and drop down to the bottom.



Size: 0,3 - 1,5 cm, 0.1 - 1/2 inches

Hydra are beautiful, but a wee bit annoying creatures. They spend their life attached to surfaces (plants, glass, filter, decoration), they can move a bit, but usually don't have the need to do that. If disturbed, they will retract their tentacles and body to small buds. They catch small creatures (copepods, Daphnia etc.) with their tentacles which can sting, making it easier for them to haul the pray in to their mouth opening. They pose no threat to adult fish, shrimp or snails (might cause some irritation if they touch the Hydra), but newborn fish and shrimp fry are in danger.

Control - (Use at your own risk) Attach a wire to each pole of a 9 volt battery. Place the ends of the wires into the tank water, as far apart as possible. If the setup is working correctly, a fine stream of bubbles should be seen from one of the wires. The Hydra will start falling after about 20 minutes. The treatment should go no longer than 3 hours, keeping an eye on conditions the whole time. A daily 50% water change for 3 days is recommended since Copper leaches into the tank via one of the wires

Bryozoa, moss animals


Size: individual creatures are only a few millimetres long, the colony can be tens of centimetres long

Bryozoans are interesting colonial creatures. They look a bit like corals with the hard skeleton structure of the colony. The individual creatures, zooids, are inside their own small part of the colony and they eat small particles (phytoplankton, zooplankton) floating in the water by guiding them (and water) towards their mouth opening with the fan like tentacles. If disturbed, the zooids will retract their tentacles inside the colony walls. They are harmless and really interesting.

Springtails, Collembola


Size: 0,1 - 0,3 cm, 0.04 - 0.1 inches

Springtails are cool hexapods. They are used as live food for fish that eat from the surface, for example small Betta species and labyrinth fishes. You can find them more often from soil or leaf litter than from the water surface, but once in a while they will appear on the floating aquarium plants. If disturbed, they will spring to safety releasing their "spring" (furcula) that's normally bent under their body. They can jump surprisingly far (several centimeters). Harmless and cute.

Mosquito larvae

Mosquitoes will tend to lay their eggs on water surfaces which are still. Try to have some water movement at the surface for prevention of eggs laying there. One can also have some fishes in the aquarium, the fishes will find them a wonderful meal.

Beetles - Coleoptera

Since it is relatively easy to tell how a beetle looks like..i won't elaborate on water beetles. There is however, one type of beetle larvae that i would like to point out, something you probably will never associate to it growing up to become a beetle since it looks so bazaar. Sometimes i find it in my pond.
Commonly known as water pennies...beetles in the family Psephenidae have aquatic larvae that look...well.. like pennies in the water.. Here are some pictures of them..



Looks pretty cool doesn't it?? And yes.. it grows up to be a beetle..
Larvae cling to the underside of rocks in fast-flowing streams and graze on algae

Next we move into the ones most aquarist will worry about...

True Bugs - Hemiptera

Lets first start of with this big fella... i don't think many of us will get this in our tanks but i'll just put it up for easy identification, just in case, one of us does.

The bug below is also commonly known as the Giant water bug and belong to the family Belostomatidae. These bugs are big!! i have seen some that are about 5- 6cm or more in the wild. They do feed on fishes and sometimes even small frogs!! so they are predatory..also if you want to catch them out of your tank...please be careful.. they do "bite" and it can be awfully painful...basically they inject you with their mouth part and pump a whole cocktail of digestive juices into your finger... doesn't sound fun does it?



Next is something very familiar..
the waterboatmen, these belong to the family Corixidae. They feed on Algae and very minute aquatic organisms..so maybe fry will not be in danger... Here is a picture of one..


Okay.. dont be confused..These next few pictures may look like water boatmen but they aren't.. they are backswimmers, family Notonectidae.
These ARE predatory so they will eat your fry.. some will also "bite" and it can also be quite painful. The difference between these guys and waterboatmen?? well.. they aren't called backswimmers for nothing.. they swim on their backs!

Top view

Bottom view - they swim with this side facing up!!

Lastly, to end of section 1, we have the water scorpion , family Nepidae. These also are BIG..but will rarely be found in your aquarium. However, these pictures are just in case. As you can see.. they have those raptor-like appendages that they use to hunt..so yes.. they are predatory and yes.. they will also "bite". Easily identified by the siphon they have on rear of the abdomen. They use this for air.

top View

Bottom view

Now, we will delve into the order Odonata.

These comprise of dragonflies and damselflies.
The larve of these 2 insect groups live in freshwater, they are also indiscriminately predatory..so they will eat your fish and also your precious shrimp. The very very obvisous thing about these bugs is the special mouth part that they have...This separates them from other orders that have a similar body shape to them but the mouthparts are different.

This is a picture of an example of the mouthparts that can be found on dragonflies and damselflies... the one picture here is on a dragonfly..

They use these like spring-loaded catapults to capture their prey at lighting speeds...looks kinda like an arm with mean jaws on the end and the whole contraption is tucked in nicely waiting to pounce...pretty cool...

Dragonfly and damselfly nymphs look rather similar... the main difference is that dragonfly nymphs do not have external gills...while damselfly nymphs do...
So after you look at the mouthpart to determind that it is one of these.. check to see if you can find external gills at the end of the abdomen... if you can.. then its a damselfly nymph..if not, then its a dragonfly nymph..
Here are examples..


So which is this?? take a guess??

Here are more bugs that look alike!!

Mayflies - Ephemeroptera

These insects also have aquatic larvae, the larvae kind of resembles the dragonfly and damselfly larvae at first glance but a closer look will reveal that they are not.. They will NOT have those raptorial-like mouthparts and they feed on pieces of organic matter such as plant material or algae and debris that accumulates on rocks or other substrates in flowing water, so your fries are not in danger..which is a different story for dragonfly and damselfly larvae.

Here is a picture of a mayfly larvae..

Stoneflies - Plecoptera

Next we have another aquatic nymph that looks like the mayfly nymph.. but it is not!! These are actually Stonefly nymphs...
Stonefly nymphs are kinda omnivorious feeding on algae, diatoms, mosses, and immature aquatic invertebrates, including mayflies and midges and so that would also include very small baby shrimp/fish.

Here is a picture of one...

Looks pretty similar to mayfly larve doesn't it??? so how do you tell which one you have in your tank??? Can you spot the differences??

Telling them apart

For mayflies..firstly, most of them have 3 cerci (tail like things coming out from the end of their abdomens)...although there are species with only 2 cerci, these are not that often eccountered..however, because they exist we cannot use this as a firm form of identification..but just as a rough guide..
What we are really looking for are gills and tarsal claws (claws at the end of the feet).

Mayflies usually have gills on the abdomen... where as stoneflies, have gills on the thoraic region (something like on the body??) These gills are sometimes hidden beneath or blends into the body form so you may have to look carefully.. here are examples of the differences..

Mayfly gills..on the abdomen..

Stonefly gills.. on the thoraic region (on the body??)

Next we also look at their tarsal claws...this one is a definite way of identifying them..

Mayfly nymphs have only 1 tarsal claw...

Stonefly nymphs have 2 tarsal claws...

And there ya go!!

Order Diptera - Flies

This order is huge...so this is going to be brief and insufficient no matter what i do. Also identification of larvae requires more detailed information, so i'll just post pictures up to help people get a general idea of what aquatic larvae of flies look like..

Most fly larvae are so small and delicious looking that they usually end up as food for the fishes...so no real danger when you spot one.

These are the most common ones i could think of...

Tipulidae - Crane Flies

Simulidae - Black flies

Free living forms that attach to rocks and what not... filter feeders.

Chironomidae - Midges (most common)

This form is outside of its "home"


This is what they usually build and live in when in the water.. little "homes" made of detritus.

Sub-order or Order Megaloptera - Alderflies, Dobsonflies and Fishflies

This is what probably looks most like a caterpillar to me...haha..
But these are mostly predatory..so they will eat things in your aquarium...please be aware of this fact when you see them....remove with caution.
Larvae are elongate, moderately flattened, have a distinct labrum, and measure 10-90 mm when mature. Mouth parts are of the chewing type, well developed.

fishfly larvae

Dobsonfly larvae

Alderfly larvae

Can you spot the differences??
Larvae bear lateral abdominal filaments (on segments 1-8 for fishflies and dobsonflies, and 1-7 for alderflies) and either a pair of anal prolegs (fishflies and dobsonflies) or a single caudal filament (alderflies). Dobsonflies also possess tufts of accesory tracheal gills under the lateral filaments of segments 1-7

LondonDragon: Found it interesting to spot what those critters in the tank are!!

Enjoy :)
Thanks LondonDragon,
Very useful info.
Might be worth a mention that all the water bugs can fly, (as can the beetles) so the adults can arrive and disappear easily - not likely to be a problem unless you have an open-topper next to patio doors though.

If you decide to keep any little critters they can get their biological clock messed up (as someone here recently discovered with a damselfly becoming adult in December).

cheers phil
My two sons aged 7 and 9 were late for school this morning because I let them go through this thread Paulo:) great they forgot all about the telly too it didn't even get turned on.:)
Hi Paulo, I've aquired the dreaded hydra and I'm trying the battery method now hopefully it will work.:)
it's been in 45 mins the little rotters are still waving at me so I'm going to run it for the 3 hrs. Die hydra die!!! No I do feel cruel but intend to put shrimp in there in about 6 mths. They will be all over the place by then.

I was wondering if this will possibly kill the pest snails?

I've removed the snails I want anyway just incase. Cheers kirk.
Hi Paulo, I've aquired the dreaded hydra and I'm trying the battery method now hopefully it will work.:)

hi Kirk,
I tried it with a motorbike 6V battery charger which worked fine, one thing I noticed was that I did it with copper flex and the 1/2cm of wire strands exposed partially dissolved and bits dropped off, so I'd suggest steel electrodes etc, I didn't have livestock so can't tell if the copper was a problem - didn't kill 2 sp of British snail...

cheers phil

:lol: writing while Kirk posted. hope the copper's not a problem..............
Hello Phil, I was thinking that but couldn't find my stainless wire. I'm using house hold speaker wire, so I'm expecting the same as you experienced, how long did it take to knock them back and how big/ltr is your tank mate? Oh and I've no live stock yet so there will be no casualties.

Thinking about it is it the copper that is killing the hydra? Or are we just giving them the chair?
Last edited:
Well this is interesting, I also have planaria, if future I shall quarentine plants I get from people it thr only way I've aquired them everything of mine was treated or new.

The wire I've put in has attracted them they moved in at speed onto the bubbling wire and I think they look zapped lol, I will put in some cat wormer after anyway.:D
don't know if you can see the planaria.

So thanks paula I've now found a wayvto find out if you have planaria too. They hate the wire that's bubbling and attack it and die. I've just put in the wormer too.
Hi Kirk,
About 130L (36"x15"x15")
the 6V charger took about 4-5 hours, I waited until the hydra turned to blobs but then also disappeared/let go.
I didn't notice any difference in the few small 1-2mm long white planaria in the tank, but I had both wires suspended in the water, not touching substrate or sides.
most of 2 types of British snail moved up to the waterline but didn't die, my waters soft so they never become a problem anyway.

I only had about 1/2cm of copper showing as it is the electricity that is supposed to kill them. I guess I dissolved about 5mm of matchstick sized copper into 130L if you want to work it out - too late for me- , and a few strands I syphoned out.
It was pre tank strip-down so I didn't worry - just made a mental note.
cheers phil
Hi all,
Thinking about it is it the copper that is killing the hydra?
I think it is the copper. It might be the oxygen, if you could get it to a high enough concentration. You can kill Planaria (and Hydra) with "Panacur" (Fenbendazole), it doesn't kill snails but "Flubenol" will (although you may need the 15% formulation).

are almost inevitable in any tank that has been set up for a while. I've got them in my water butt, and even in buckets of water in the garden. I've no idea how they got there, but they are almost universal in any form of fresh water.

None of these chemicals kill leeches, because they are Annelid worms, and I think some of the cases of the chemical "not working" are because the Planaria are actually small, non-blood-sucking Leeches. These are very Planaria like (same size, often white or translucent), but they move by "looping", rather than gliding.

cheers Darrel
I should never have read this thread! Although very informative I am disturbed... I hate bugs [shivers down spine]! But thank you - a really good reference thread.
why did i open this thread :lol:

I hate bugs like these...I had a damsel fly larvae nymph thing in my big tank once before, did not like it one bit haha
why did i open this thread :lol:

I hate bugs like these...I had a damsel fly larvae nymph thing in my big tank once before, did not like it one bit haha

I Love things like this:woot: Its interesting to watch them go thought there life cycle. And good for the Grandson to watch and learn about nature :)
Brings back memories of pond dipping - nets and white sample trays...

I don't mind the above too much its the leeches and Oligochaete worms that turn my stomach :sick:

P.S. This thread should come with a warning - Do Not View Whilst Eating.
Last edited: