Do jumping spiders run towards danger?

Shenade Annie Kerketta, Amity University Kolkata

For all living beings, movement is a vital factor that helps determine whether an organism is biological or non-biological. In this article, we are going to learn about the “itsy bitsy spider” once again. Salticidae, the jumping spider, is one of the most visually accomplished arthropods. These spiders use two sets of their eyes, primary and secondary, to distinguish between organisms exhibiting biological motion.

When visually observed movements of an organism produce a statistically idiosyncratic identifiable design it is termed Biological motion. Jumping spiders rotate towards their moving object of interest. These rotations are termed saccades. This article explains the experiment, carried out, to know about this selective behavior. How should an organism move to gain a jumping spider’s attention?

The recent 2020 experiment:

M.semilimbatus was used as the subject in this experiment. There were 31 females, ten males, and 19 juveniles, 60 in total. Spiders were placed on spherical treadmills (one spider per treadmill) which would measure the rotations produced by them. Fic Trac software mentioned by Moore and colleagues was used to analyze the orientation of the spherical treadmill. This provided with the saccades data. The stimuli used for this experiment was a side view of Salticus scenicus. The stimuli were represented using a point-light display.

Each spider underwent four trials paired with five stimuli conditions.

1. Biological motion(depicting an organism).
2. Scrambled motion(depicting semirigid organism/object).
3. Random motion(depicting nonbiological organism/object).
4. Silhouette(used as control).
5. Ellipse(depicting structured object/organism).

 Example of a trial:

1. Biological paired with scrambled
2. Biological paired with random
3. Biological paired with silhouette
4. Biological(will show only biological motion).

In a similar order, trials took place for each stimuli condition per spider. The spider placed on a spherical treadmill was set in front, fourteen cm away from a screen. The screen presented a point-light display of the paired stimuli conditions simultaneously entering from opposite ends. The stimuli would reach the center, pause for 1.5 seconds and, then disappear.  The saccades produced during the display of stimuli were recorded, through the spherical treadmill. Two of the conditions were carried out on one day. The other two were carried out after a gap of three days. Before each trial started, the spider was set to glare at a blank screen to calm down. It is known as habituation time(five minutes).

Results and discussion:

The results show that spiders rotated towards ellipse over the silhouette, random over biological and scrambled. It showed no difference between biological and scrambled conditions. These results signify that jumping spiders direct more of their attention towards less realistic objects or organisms. It has a good explanation.

Jumping spiders use two sets of eyes to perceive and analyze moving objects or organisms. Secondary eyes analyze motion and produce saccades. If it is unable to perceive, it passes the information to the primary eyes.  Primary eyes receive the information that something needs to be analyzed further. Hence, the saccades are produced towards the unrecognizable body while keeping an eye on other identifiable bodies. The primary eyes will now focus on the unidentifiable bodies. Jumping spiders are not that social, thus justifying this behavior further.

Conclusion:

Through this experiment, we find that jumping spiders perceive organisms through motion using two sets of eyes. This feature is also called “animacy detection” which is different for different organisms. Animacy detection implies distinguishing between inanimate and animate objects. Organisms perceive in distinct ways like locusts calculate distance through motion parallax. These saccades are rapid rotations just for inspection. This ability does not lead a spider towards danger. It just helps the spider to inspect an unfamiliar object. There are more of such abilities carried out by secondary eyes that are yet to be studied. It looks like “itsy bitsy spider” does a lot more than just sitting on a wall.

Also read: https://bioxone.in/news/worldnews/cardiomyocytes-infected-with-sars-cov2-recruit-immune-cells/

Reference:

1. Agrò, Massimo De, et al. “Perception of Biological Motion by Jumping Spiders.” PLOS Biology, vol. 19, no. 7, July 2021, p. e3001172. PLoS Journals, doi:10.1371/journal.pbio.3001172. https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001172

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