This disappearing spider trick is a simple Halloween science activity and a great refraction demonstration.

Children can watch as a drawing of a spider disappears when water is poured into a glass over the image.

Disappearing Spider Trick

You’ll need

Glass cup or jar
Drawing of a spider on a sheet of paper
Water

Instructions

Place a drawing of a spider under the glass.

Slowly fill the glass with water and watch the spider disappear.

Why does it work?

Light (from the sun or artificial light) travels in a straight line, bounces off objects, and enters our eyes, allowing us to see things. Generally, there is little or no refraction of light as it travels through air.

However, when you pour water into the glass or jar, the light from the spider drawing is refracted ( bends ) and doesn’t reach your eyes, which is why the spider seems to disappear.

More science ideas for Halloween

Make a fizzy pumpkin lava lamp.

Try one of my other spooky Halloween Science Experiments, which include jumping ghosts, a spooky noise maker, or fake blood.

Or how about giving one of my creepy Halloween STEM challenges a go?

Last Updated on October 2, 2024 by Emma Vanstone