The secretive Mantis shrimp looks amazing, like an (often) colourful cross between lobsters and shrimp, I’ve even eaten them in Vietnam and stalked them across the sea floor in Indonesia. However, you certainly don’t want these common live rock stowaways and efficient predators in your tank as pests…
Beware the Mantis!
Mantis shrimp dine on small fish or other invertebrates and live in crevices and holes. Big species can grow up to 30cm long. They can often be very hard to catch because of their cunning and have even been known to smash aquarium glass! They have predatory appendages at the front like preying Mantis’s these can either be spikes (spearers) or powerful clubs (smashers also known as “thumb splitters” by fishermen) which are unleashed lightning fast and can easily do you some damage if you try to catch them by hand.
Mantis shrimp can often be hard to detect but if you hear loud clicking (made by a smasher, spearers don’t make a sound) or have a series of smaller fish go missing, this is a good sign one is present in your tank.
Getting rid of them…
Unfortunately there is no easy way to get rid of these fish and invertebrate hunting beasties. Observation at night (when they are active) can reveal where their hole is in the rock (or follow the sounds). If you have found their hole you can remove the rock and dry it for a few weeks to kill the mantis, or keep it in a bucket of seawater to try and extract it out with food then trap it.
Sometimes a complete tank teardown will be necessary to find and remove the Mantis, manual rock removal is usually the best bet.
Luring them into a trap with bait can sometimes work well, but as they are very fast and devious this can sometimes take a long time or never work.