Why Does an Octopus Have Ink?

Whenever I visit the Aquarium, I always fall in love with the jellyfish and the octopi.  Watching an octopus move is just so mesmerizing!  They are also known to be very intelligent creatures.  And like most squid, they have an ink sac (which is so very cool if you have ever dissected a squid).   In this quick, simple, activity, your superheroes are going to observe and explore why squid have an ink sac.

Here’s what you need to get started:

  • water
  • 1 clear glass
  • 1 small cup
  • black food color/watercolor/paint
  • dropper (I always save the ones I get from the pharmacist!)
  • small plastic octopus toy
  • small plastic shark (optional)


In the small cup, mix some water with black paint/food coloring or water color.  I had none of those so I mixed red and blue food coloring to make a dark purple.  This will be the “ink”

Fill a clear glass halfway with water.  Add the plastic octopus to the water.


Discuss how the octopus looks in the water.

Using the toy shark, I showed my son that a predator was approaching the octopus.  What was the shark going to do?  What could the octopus do to protect itself?


Using the dropper, add “ink” to the glass with the octopus.  This models that the octopus will release dark ink as a defense mechanism.  What happens to the water as the ink is added?  Can you see the octopus?

IMG_5318 IMG_5319

After some discussion, my son decided to play with the shark and the octopus and ink.  It kept him busy for awhile as he engaged in pretend play and the narrative he added was so cute to listen to.


Extension: Try this in a large shallow dish by adding the shark and the octopus.  Add the ink just on top of the octopus.  What happens to the ink?  Can squirting ink alone help the octopus protect itself?  What other defense mechanisms might they need to help protect them from predators?

The Science behind the Activity:

This little activity is a simple model of how an octopus, like most squid (but not all squid) use an ink sac as a form of a secondary defense mechanism.  By squirting the ink, the predator gets confused AND the ink often has a smell associated with it that also deters predators.  With the smell and the spray shocking the predator, it allows the octopus to use its quick tentacles to escape before the ink dissipates.

To see where I got my idea from, click on the following link:


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