Thousands of spiders sometimes rain directly from the sky? Scientists explain the reason behind this bizarre phenomenon of nature

Imagine looking up at the sky and seeing hundreds or even thousands of spiders seemingly floating above you. While it sounds like a scene from a horror film, the phenomenon has been documented in countries including Australia and Brazil. Scientists say the explanation lies in an unusual spider behaviour that allows the tiny creatures to travel through the air.

Often described as 'spider rain', the sight can leave people frightened and confused. However, the spiders are not falling from the clouds. Depending on the species and circumstances, the spectacle can be caused by mass migration through the air or by spiders gathering in enormous webs.

How Spiders Fly Through the Air?

One explanation for spider rain is a behavior called ballooning, IFL Science explains.In this process spiders climb to high points such as plants and trees and throw out fine threads of silk to help them catch the air.


This is a common technique used by young spiders and smaller adults to move away from where they were born and find a new home. By dispersing, they can escape competition with other spiders for food and space.

Entomologist Robb Bennett described the process to National Geographic in 2015 as “a reverse-parachute effect – they're going from the ground into the air”.

Although ballooning is a regular occurrence, it usually happens on a small scale and goes unnoticed. When large numbers of spiders take flight around the same time, however, their silk threads can become visible across the landscape, creating the impression that spiders are raining from the sky.

Why thousands of spiders may appear together

Weather conditions can help explain why these events sometimes involve huge numbers of spiders. Biology professor Todd Blackledge told Live Science that a group of spiders may be ready to disperse but wait until conditions become suitable.

“What's thought to be going on is that there's a whole cohort of spiders that's ready to do this ballooning dispersal behavior, but for whatever reason, the weather conditions haven't been optimal and allowed them to do that. But then the weather changes, and they have the proper conditions to balloon, and they all start to do it,” he explained.

The spiders use air currents to travel, but wind is not necessarily the only force involved. Research published in 2018, led by Dr Erica Morley, found that atmospheric electric fields could also trigger ballooning and provide lift even when there is no air movement.

Spiders can travel considerable distances using this technique. However, the journey is risky, with many dying because of predators or unfavourable weather.

Brazil and Australia incidents

In 2019, videos showing hundreds of spiders apparently hanging in the sky went viral after being filmed in a rural area of Minas Gerais, Brazil. The Guardian reported that residents had witnessed the phenomenon during hot, humid weather.

The footage was recorded by Joao Pedro Martinelli Fonseca, who said the sight left him “stunned and scared”. His grandmother, Jercina Martinelli, told a local newspaper that similar scenes had occurred at dusk on particularly hot days.

However, biology professor Adalberto dos Santos offered a different explanation from ballooning. According to the Guardian, the spiders belonged to the species Parawixia bistriata and were hanging from a huge web built to catch prey. The web was so fine that it was almost invisible to the human eye, making the spiders appear to float in the air.

A similar spectacle was reported in Goulburn, in Australia's Southern Tablelands, in 2015. According to Smithsonian Magazine, residents reported unusual spider activity, with fine silk covering parts of the landscape.

Heavy rain and flooding can also result in such scenes, with spiders moving upwards into vegetation using their silk threads.