Some of the most fascinating live you will find in your aquarium is life that has appeared seemingly by itself. The critters that enter your tank uninvited are known as hitchhikers.

Some hitchhikers are a great addition to your tank, you can see some of them in my Top 5 Saltwater Hitchhiker (Good Guys) post, others, like the ones listed here are the ones you really want to avoid!

Gorilla Crab

5. Crabs

Missing one of your favorite fish? Maybe it’s jumped out of your tank? Maybe it has a big slash down it’s side?

It could just be that you have a nuisence crab in your tank.

Not all crabs are bad news, but some of them can cause utter devistation if they are allowed to enter your tank unseen. They can actively hunt your fish & corals, causing £100’s of £1000’s of pounds worth of destruction over a single night.


4. Flat-worms

Not all flatworms are bad. But the ones that are bad, are very very bad.

Many species have a taste for corals and will think nothing of destroying whole colonies, especially expensive SPS colonies.

Some predatory fish species will help keep their numbers at bay, but once you have a flatworm infestation they are very difficult to remove from your tank completely.

3. Aiptasia & Majano Anemones


Just like the pretty & decorative anemones we choose to put into our tanks, the Aiptasia & Majano Anemones can sting & irritate your corals.

Not only are these anemones not as aesthetically pleasing as things like Bubble Tip Anemones, they also grow and spread quicker than most other coral species.

Even the tiniest little bit of flesh of one of these anemones can regenerate into a full adult anemone, leaving you with a constant battle to try and keep on top of the number of them.

2. Mantis Shrimp

Mantis Shrimp

Clicking sound in you tank? Fish missing? Could be a Mantis Shrimp.

Known as finger splitters, these predators will actively hunt your fish, damage your live rock (which cause a collapse) & the nasty little blighters have also been rumoured to break aquarium glass.

Granted, some people choose to keep them as pets, but they can cause utter devastation in a reef tank if they have come in as a hitchhiker.

1. Bobbit Worms & Fireworms

Bobbit Worm
Bobbit Worm

Unlike the Bristleworms, which are often a welcome addition to your clean-up-crew, the Bobbit Worm & Fireworms are not helpful & cause many reef keepers headaches!

Active predators that bury themselves in sand and live rock, stalking your favourite fish, waiting to snatch them out of the water at night.

Fire Worm
Fire Worm

These worms are fast breeders, hard to catch & can grow to enormous lengths before they are ever seen in a tank.

Preventing hitchhikers from entering your tank

Inspect every piece of live-rock and coral you put in to your tank & dip where possible. In an ideal world, you should quarantine anything you plan on putting into your tank for a minimum of 4 – 6 weeks. This will allow you to hopefully spot any unwanted guests and remove them from the quarantine before they enter your main tank.


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