Mysterious jump of Adanson spider

Adanson jumping spiders have a unique distance judgment that helps them pounce on the prey without spider web.

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That ability is obtained through observation of the green light of the spider.

There are many different visual systems used by organisms to accurately judge distance and depth. For example, humans have two eyes eyesight. Because the human eyes are far away from each other, they receive visual information from different angles, and our brains use them to determine distance by trigonometry.

Other animals, such as insects, adjust the focal length of the lens in their eyes, or move their head from side to side to create an effect called motion parallax - those closer objects will move through their visual field faster than distant objects.

Adanson jumping spider

However, the Adanson spider ( Hasarius adansoni scientific name) does not have any focal adjustment system. They have so close eyes that it is impossible to judge distance in a human way, nor to use moving parallels in the hunting process.

So how can they feel the image depth? According to specialist Scienc e, researchers at Osaka University (Japan) discovered Adanson spiders correctly guess the distance by comparing the blurry image of an object with a clear image , a method called image. defocus (temporarily translating "image deflection" ).

Adanson spider has 4 eyes close together: 2 eyes between big and 2 small outer eyes. It uses two outer eyes to sense the movement of objects, such as flies, and uses two main eyes to focus on prey.

According to Akihisa Terakita, the lead researcher, instead of having a single light-stimulating receptor cell, the retinas in the two main eyes of the Adanson spider have up to four layers of photoreceptors. When expert Terakita and colleagues looked at its main eyes, they discovered that the two most closely-bound layers contained ultraviolet-sensitive pigments, while the deeper layers contained sensitive pigments. with green.

However, because of the specific distances of the cell receiving light stimulating light compared to the lens of the eye, green light is concentrated in the deepest layer, while the green sensitive retinal layer remains Only receive blurry images.

The researchers hypothesize that Adanson spiders have judged the distance based on the degree of deflection in this translucent image layer, which is proportional to the distance from an object to the lens of the eye.

To test this, the researchers placed an Adanson spider and 3-6 fruit flies into a cylindrical plastic chamber inside a white foam container. Then they flooded the plastic chamber with different colored lights.

If green light is important to spiders, they will probably misjudge the distance to jump on the prey when lacking this light. The results showed that spiders could grab fruit flies easily under green light, but often misjudged under red light.

Japanese experts concluded that blue light created the image blur needed for spiders to determine the distance to their prey.

Mr. Terakita and his colleagues have not determined whether any other animals use distance judgments like Adanson spiders, but they are confident that their new finding on how to judge the spiders' distance is can be useful for designing visual systems for robots in the future.