These Giant Yellow And Blue-Black Spiders Are Not Scary, But The 'Shyest' Ever Seen, Says Study

The giant spiders were found to remain immobile for over an hour after a stimulus, unlike most other spiders, which remain immobile for under a minute on being provoked.

There are some giant spiders with yellow and blue-black colours on their bodies which may appear scary, but are the "shyest" ever documented. These are jorō spiders (Trichonephila clavata), which have been introduced in the southeastern United States. 

A team of researchers led by the University of Georgia found that both Trichonephila clavata, and its cousin, Trichonephila clavipes, commonly known as the golden silk spider, remain immobile for over an hour after a stimulus, unlike most other spiders, which remain immobile for under a minute on being provoked. This behaviour is unprecedented, and suggests that spiders belonging to the genus Trichonephila are the "shyest" ever documented, a study, published May 15, 2023, in the journal Arthropoda, said. 

What are jorō spiders like?

Jorō spiders weave exceptionally large webs which are one metre to two metres in diameter. They are found on bushes, trees and in human dwellings. The study found that jorō spiders are highly tolerant of human-modified landscapes. 

Andrew K Davis, the lead author on the paper, noticed dozens of webs made by the species connected by support strands, the study said. All these webs formed a "colonial web". This indicates that jorō spiders are invasive and opportunistic. 

What was the aim of the study?

The aim of the study was to understand the behaviour of jorō spiders in their introduced range, evaluate how they react to perceived threats, and understand how well they can tolerate anthropogenic disturbances.

How the study was conducted

As part of the study, the researchers collected mature females of both Trichonephila clavata and Trichonephila clavipes, along with three locally common orb-weaving species in Georgia. The team evaluated the time spent by the spiders immobile after experiencing a mild disturbance, such as a brief puff of air. 

The authors noted in the study that they collected similar "air puff response" data for five other North American species published in studies, and collectively, obtained 453 observations of freezing behaviour across 10 spider species.

What kind of behaviour did Trichonephila species display?

The authors noted that both Trichonephila species displayed an exceptionally prolonged thanatosis reaction after a mild stressor, compared to other spider species, whose reactions lasted for only minutes. Thanatosis, also known as death feigning or tonic immobility, is an anti-predator strategy adopted by diverse prey usually after physical contact by the predator, according to the National Library of Medicine. It is a temporary state of motor inhibition believed to be a response to situations involving extreme fear. 

According to the authors, the extreme thanatosis response observed in both the Trichonephila species appears to be unprecedented, based on their survey of previous studies. 

They remained in the frozen state for over an hour, while most other spider species which exhibited similar behaviour remained in a frozen state only for one minute to two minutes.

Why Trichonephila species exhibit freezing behaviour

According to the study, the prolonged response to perceived threats observed in Trichonephila spiders could be a unique form of defensive strategy within the species that has evolved because of the increased level of predation within colonial webs compared to solitary webs. 

The authors ruled out "large body size" as the reason behind the spiders exhibiting freezing behaviour because Argiope spiders are of similar size, but do not display a prolonged startle response. 

Since Trichonephila spiders have a unique tolerance of urban landscapes, the surprising behaviour shown by them is "noteworthy", and points to how members of the genus are exceptionally shy, the authors said. 

They have an "extremely shy" and "non-aggressive" personality, the study said. 

The fact that both Trichonephila clavata and Trichonephila clavipes remained immobile for over an hour suggests that this method of reacting to stressors allows spiders belonging to this genus to tolerate continuous disturbances in urban environments by remaining motionless throughout each disturbance, instead of fleeing, the authors concluded.