When I first started out fishkeeping, I'll admit I was a bit of a scaredy cat. I was already a little bit nervous around the fish, let alone the much smaller organisms living around the tank - and it turns out, there's a lot of different kinds of six, eight and no-legged creepy crawlies that can inhabit our aquariums. The good news is, the vast majority of these aren't going to do any harm to you or your fish.


Whilst it'd be ideal to sort these bugs based on how they look (such as how many legs they have), some invertebrates can be too small to see clearly with the naked eye - and if you're anything like me with phone cameras, they seem to become more blurry once they're photographed! The way we're going to sort these guys out is by figuring out what part of the tank they're living in. Most of the invertebrates have a specific niche, or a way of living, that can be identified with a bit of observation. For example, your classic snail might live mostly on the glass, or it might live under the gravel.


red brown ramshorn snails

Above: Red and Brown Ramshorn Snails.


In and Around the Substrate

If you've ever looked at the gravel or sand in your tank, it might be moving a little. Of course some burying fish may do this, but sometimes it's something a bit smaller and creepier. More often than not it'll be Malaysian Trumpet Snails, which are often found turning over the sand and munching on spare food. 


Tubifex and Blackworms

Commonly used as a live food source for fish, on the rare occasion you might find Tubifex or Blackworms in your aquarium. Typically these get eaten up pretty quickly, so they aren't often found unless you've introduced them specifically. Tubifex worms belong to the Tubifex genus (as the name might suggest), while Blackworms belong to the Lumbriculus genus. Despite being in different families, both of these worms look similar - they tend to be reddish-black in colour, a few millimetres in diameter and range from 5 to 15cm in length. Lumbriculus tends to be shorter and thicker, and "swim away" if disturbed, while Tubifex tend to be long and thin, and will "retreat" into the substrate when disturbed.


Both of these species like to live in the substrate (whether that's mud, pebbles, sand or just debris) and will often be seen either digging around looking for food or staying in one spot, half in the substrate and half dancing (or just sitting around) in the water column. Despite being a little bit creepy and a little bit prickly looking, both of these guys are harmless to fish and will usually be eaten by fish.


It's worth noting, however, that Lumbriculus tends to be the preferred species to culture for fish food, as Tubifex can be known for being a host for internal parasites.

tubifex and blackworm

Above: A good food source, the left is believed to be Tubifex tubifex and the right is believed to be Lumbriculus variegatus.


Detritus Worms

It's a bit hard to give an exact explanation of what counts as a Detritus worm, but the many 5-10mm white squiggles can be almost impossible to identify with the naked eye regardless (to add to the confusion, Tubifex may sometimes also be referred to as Detritus worms). Detritus worms pretty spiky looking, but are non-parasitic, and usually enjoy feeding on, as their name implies, detritus (basically, dead stuff and poop). They can be found in the substrate behaving much like the above Tubifex and Blackworms, but can also be found on the glass and even on the surface.


An over-abundance of these may be a sign that your tank is too high in stocking or you may be overfeeding, but overall these bugs are harmless for your fish (and may even make for a good snack). 


Above: Both of these may be called Detritus worms by fishkeepers. Left is believed to be Stylaria and right is believed to be of the Aeolosomatidae family.


Malaysian Trumpet Snails

Fortunately, Malaysian Trumpet Snails (MTS) are pretty easy to identify - but unfortunately, they can also come in pretty big numbers. However, other than their large population size and looking unsightly to some, Malaysian Trumpet Snails are both harmless and can even be desirable. Some fish such as large loaches enjoy feeding on MTS, and the snails themselves can also be useful for turning over the substrate in your tank.


An interesting fact about Malaysian Trumpets is that almost all of those found in the aquarium are likely to be female! MTS are livebearing (and thus don't lay eggs), however only the females can reproduce asexually (have offspring without a male).

malaysian trumpet snail

Above: A young Malaysian Trumpet Snail.



Amphipods are pretty unusual in the aquarium as (like Tubifex and Blackworms) they make for easy snacks for fish, however we've included them as they're almost kind of cute! Amphipods are small, shrimp-like crustaceans that you may find "scooting" or "hopping" along your substrate. It's possible large ones may eat fry, but otherwise Amphipods are harmless to your fish.


Above: A marine Amphipod species. Photo © Hans Hillewaert / , via Wikimedia Commons



On The Glass

Have you ever checked out your tank a few hours after the lights were off? You might notice a few different types of creepy crawlies that prefer slightly dimmer conditions, such as snails.


Other Snails

Probably the most common "pest" found in aquariums, you can read all about snails here. Easy to identify, snails are a "love 'em or hate 'em" kind of thing. As they are harmless, I personally appreciate the hard work that snails put in feeding on debris and leftover food - they also make great food for fish like loaches and puffers. Common snails include Brown Ramshorns, Pond Snails, Bladder Snails, and the Malaysian Trumpet Snail introduced above.

ramshorn pond snails

Above: A Brown Ramshorn Snail (left) and a Ladder Snail (right).



Although they aren't technically true Limpets, what we call Limpets in aquaria look a little bit like a snail with a hat (instead of a twisting shell). Limpets tend to only reach a few mm in length, make good snacks for fish and may be more visible at night - they are also harmless (and, in my opinion, pretty cute!).

freshwater limpet

Above: A freshwater Limpet.



Now, Planaria (a type of Flatworm) do tend to get a few people freaked out, however these guys aren't usually as scary as they seem. Flat in appearance (hence their name) with a characteristic arrow-shaped head (if large enough to see), Flatworms are almost always harmless to fish and are generally more unsightly than anything. Large Flatworms may predate on fry, however this is not common and their populations can be controlled by preventing overfeeding and overstocking.


Above: A Flatworm species, Photo By Eduard Solà (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons



Okay, so with these guys a little bit of nervousness is warranted. Hydra are pretty fascinating organisms but they do have a downside - the end of those tentacles are capable of stinging. The first thing to note is that there are several kinds of Hydra, which typically present in two forms: The first are larger and white, which are the slightly worrisome kind. The second are smaller and green, and are a bit more harmless and tend to feed on Daphnia and Brine Shrimp (in fact, the ones photographed below were found in a tank being used to raise Corydoras sterbai fry without any casualties). Interestingly, the green Hydra have a mutualistic relationship with single-celled photosynthetic algae Chlorella, which may be why they tend to be less predatory towards fish.


The second thing to note is that generally, the larger white variety aren't too much to worry about - these guys aren't going to take down a tank of fish! They have, however, been caught occasionally sneaking fish fry. Hydra can be a bit difficult to eradicate from a tank and may sometimes go away on their own (as larger fish enjoy eating them, despite the stringers). The best methods appear to be creating a slightly salty tank, syringing salt straight onto them (this seems to be the most effective method) or getting a fish that eats them (such as Blue Spot Gourami, Trichopodus trichopterus, however we recommend fully researching any fish before purchase). Some say that Praziquantel may eradicate Hydra, although in the experience of myself and some others, it was not successful in affecting their populations at all.

green photosynthetic hydra

Above: Green, photosynthetic Hydra.



Above The Water

Those that live above or on top of the water tend to be too small to identify, and are often seen hopping around on stagnant water. There's usually two possible creepy crawlies that live here - Mites and Springtails.



Mites are part of the Arachnid class, and sometimes things with eight legs can sound a little scary - fortunately, Mites living on the surface of your tank are both very small and very harmless. They can be hard to identify with the naked eye, and can be mistaken for Springtails or even tiny, bouncy specks of dust. If you find Mites a little unsightly or creepy, one way to reduce their numbers is to increase the water flow at the top of your your tank, creating surface agitation that these little guys aren't too fond of. Otherwise, they serve a bit of a purpose as free fish food for top-dwelling fish.

mites microscopic

Above: Aquatic Mite. These guys are so small they're best viewed under a microscope!



Springtails are the Mites' 6-legged friend. They can be found bouncing around on the surface of your tank water, although they've even been found living in cansiter filters. Like Mites, they are small and harmless, and are also a source of food for fish. To reduce their numbers, you can try increasing surface agitation, or preventing overfeeding.

aquatic springtails

Above: A species of aquatic Springtail. Photo by Christian Fischer [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons



Bugs Not Covered


pond snail eggs

Above: Some Pond Snail eggs forming in a jelly-like sac. Almost so ugly, they're cute!


Aquatic invertebrates are incredibly diverse, making it tricky to cover every different kind of bug out there. If you didn't find what you're looking for above, feel free to check out our Gallery for more photos of inverts that can be found in the aquarium. Alternatively, our Contact Us is always open, where we're happy to try to help with identification (although we can't promise anything)!