Like many other crustaceans, water fleas are very sensitive to light. They have a light-sensitive organ, also called Ocellus, with which they can swim in the direction of the light.
In the video we see a water flea in a Petri dish. It is captured in a narrow beam of light aimed at the surface of the water. It is surprising to see how actively the water flea reacts to light. If we turn off the light (lights low), the water flea does not respond. As soon as the light is switched on again (lights high), the animal is startled and flees quickly. Moments later it returns to the light again. This game can be continued without end.
Many studies and experiments can be found in literature on the internet, that tell about the migration behavior of water fleas under the influence of light. Links are made with, amongst others, the search for food and defense against hostile predators. Simple experiments can be carried out by yourself at home.
Note: It seems that the frequency of the flea’s heartbeat decreases in the darkness. This should be further investigated whether this is really the case.
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