Blood Rain, Blood Snow: Curse or Science? — International Microorganism Day

**Blood Rain, Blood Snow: Curse or Science?**

By Navitri Chandra Naidu

Mythology. Adventurous fantasy woven together with virtues and grounded in reality and the truth. These are the ways in which we describe the wondrous phenomenon that took place in times long past. One example of such a phenomenon is blood rain and blood snow.

Blood itself, in the context of various mythologies and perspectives, has a symbolic significance, such as sacrifice, purification, a reminder of our mortality, or even that it is forbidden. But when it comes to ‘rain of blood’ or ‘tears of blood’, most of them refers to the bad omen or the curse of the gods. Although, as whimsical as it sounds, would you ever entertain the possibility of such phenomenon ever happened or is it merely a metaphor used in mythology to captivate the readers?

To understand more about blood rain and blood snow, let us embark on a journey through history that will take us from ancient Greece, through mediaeval Ireland and on to the 21st century.

Ancient Times

Figure 1: Illustration of the Trojan war

One of the earliest references to the blood rain was mentioned in the Iliad, an epic poem written by the Greek poet Homer, which depicted the famous story of the Trojan War and the Greek siege of the city of Troy. According to the Iliad 16.459,

"The sire of gods and men assented, but he shed a rain of blood upon the earth in honour of his son whom Patroclus was about to kill on the fertile plain of Troy far from his home"

During the Trojan War, while Patroclus and Sarpedon were engaged in close combat, Zeus expressed to his wife, Hera, his desire to save his son, Sarpedon, from his destined death at the hands of Patroclus. However, Hera cautioned him against interfering with destiny. The passage above depicted Zeus’ helplessness, grief, and emotional attachment to Sarpedon, which led him to cause the unnatural event described. Additionally, in this context, ‘rain of blood’ is also considered as ill-omened grace bestowed by Zeus.

In addition to the other stories from the ancient Greek mythology, similar occurrences of the blood rain were also mentioned in several other mythologies such as the Indian epic Mahabharata, the Chinese mythology, as well as the enslavement of Egyptians during the Roman empire.

Figure 2: Illustration of Aristotle and his colleague discussing the history of animals
Source: universal history archives / getty images

Similar to blood rain, the origins of blood snow can be traced back to the ancient times. It was first mentioned in Aristotle's Historia Animalum, or 'history of animals', a book written in the fourth century B.C. by the renowned Greek philosopher, which has a significant influence on the field of zoology. In book V, Aristotle wrote the following:

“And, by the way, living animals are found in substances that are usually supposed to be incapable of putrefaction; for instance, worms are found in long-lying snow; and snow of this description gets reddish in colour, and the grub that is engendered in it is red, as might have been expected, and it is also hairy. The grubs found in the snows of Media are large and white; and all such grubs are little disposed to motion”.

Although no further explanations were provided for his discovery of blood snow, other than the fact that it had been misidentified as mineral deposits or pollen up until the early 1900s. Perhaps the later era will shed light on the actual cause of this phenomenon.

Middle Ages

Figure 3: 1888 illustration of the extreme blood rain at Aix, France in July 1608
Source: Science Photo Library / Alamy Stock Photo

Throughout the Mediaeval and Renaissance periods, there are a number of reports pertaining to blood rain. One of these records is mentioned in the Chronicum Scotorum, which is a collection of mediaeval Irish chronicles covering from prehistoric times until 1150: “it rained a shower of blood, which was found in lumps of gore and blood on all the plains in Ciannachta, at Dumha-na-n Deisi especially” (in the year 878). It was believed that the early Druids, who were thought to have the ability to bring down flaming and bloody rain, were responsible for this phenomenon.

Limited understanding of these unexplained occurrences throughout history instilled fear in everyone, who immediately referred to the sign as a bad omen or indicating that there were curses given upon them. Fortunately, the era of science is approaching and science, as the savior of humanity, has played a vital role in shedding light on the mystery of blood rain and blood snow.

Modern Era

One of the most famous blood rain or red rain phenomena recorded in the modern era was the red rain in the southern Indian state of Kerala and Sri Lanka, which first occurred in 1896 and has occurred several times since. However, the first well-documented event was during the monsoon season in 2001, when the red rain was first experienced in the Kerala districts of Kottayam and Idukki on July 25th and was frequent for ten days before becoming subdued by September 23rd. Millions of tiny red cells about 10 micrometres in size were detected in the rain. The rain was mostly red, though there were a few unconfirmed reports of other colours such as black, green, grey, and so on. This phenomenon was initially believed to be related to a meteor airburst that occurred a few hours before the first occurrence of red rain on July 25th, 2001, as reported by Kottayam district residents who heard a loud explosion; however, the theory was retracted and a report published by the Centre for Earth Science Studies (CESS) and Tropical Botanical Garden and Research Institute (TBGRI) in November 2001 stated that the particles from the rain were identified as spores from a lichen-forming algae belonging to the genus Trentepohlia.

Figure 4: Particles of the red rain under 1000x magnification
Source: Louis & Kumar (2006)

In 2015, a team of Indian and Austrian scientists collaborated on the publication of a scientific journal in which they determined that the species of algae responsible for the blood rain in Kerala in 2001 was Trentepohlia annulata, a green algae species native to Europe that had no previous records of existence in India. Despite the fact that these two countries are geographically separated by a significant distance, it is hypothesised that the distribution of the algae cells over a distance of 7,000 kilometres occurred through "clouds over ocean", an aerial dispersal of the European species to the Indian subcontinent.

Figure 5: A puddle of blood rain in one of the residents’ white basins
Source: Joaquín Pérez

In the autumn of 2014, another incident of blood rain occurred in some of the villages in Zamora, Spain. The residents of Zamora were perplexed by the fact that a blood-like substance had turned their white basins red. This piqued the interest of Joaquin Pérez, a scientist from the neighbouring village of Ayoó de Vidriales, who collected some samples and brought them to the University of Salamanca for further examination. In contrast to the situation in Kerala, the cause of this blood rain was identified to be Haematococcus pluvialis.

First described by J. Von Flotow in 1844, Haematococcus pluvialis is a green microalgae found in freshwater environments and temporary water bodies such as lakes, natural and man-made ponds, ephemeral rain pools, and birdbaths, normally in temperate climates such as those found along the European Atlantic coast and in North America. According to a study published in the Spanish Royal Society of Natural History Journal, there are no occurrences of this species in the reservoirs surrounding the village of Ayoó de Vidriales or Sanabria Lake, where another incident of blood rain occurred in the autumn of 2014, indicating that the origin of this species cannot be determined, although it was hypothesised that it originated in North America.

Figure 6: Microscopic view of the microalgae *Haematococcus pluvialis*
Source: Getty images

The life cycle of H. pluvialis consisted of four stages, with the first three (macrozooids, microzooids, and palmella) referred to as the green stage and the fourth (hematocysts) as the red stage. Under favourable conditions, H. pluvialis cells remain green; however, under unfavourable conditions such as high salinity, exposure to high temperature (30-33°C), high irradiation, nutrient deprivation, as well as the combination of these conditions, H. pluvialis cells produce a large amount of carotenoid, particularly astaxanthin, resulting in bright red coloured cells which can be seen in Figure 6.

Figure 7: *Haematococcus pluvialis* Flotow observed in Norway by Johan Sirnes

New arctic strains of H. pluvialis were isolated in 2013 from a small freshwater basin in the rock on the island of Blomstrandhalvøya in Svalbard, Norway. This strain has the ability to survive and produce astaxanthin at temperatures as low as 4 to 10 degrees Celsius, whereas H. pluvialis normally grows at 20 to 27 degrees Celsius. However, it is not uncommon to find snow algae with similar characteristics to H. pluvialis, as red-coloured snow caused by various snow algae is typically discovered in alpine and polar regions of the world and is also the cause of the ‘blood snow’ phenomenon.

In 1818, Captain John Ross was sent to an arctic expedition in attempt to find the 'Northwest Passage,' and on the way back through Baffin Bay, between northern Greenland and Canada, he noticed blood-like snow and brought some samples back to England to be examined further. He sent the liquified snow sample to Robert Brown and Francis Bauer, who both provided different explanations, with Brown believing the species was a unicellular algae and Bauer identifying it as a new species of fungus, Uredo nivalis. However, it wasn't until the early twentieth century that the species was officially identified as by its algal nature and given the name Chlamydomonas nivalis, or also known as 'watermelon snow,' 'blood snow,' 'pink snow,' and 'raspberry snow.'

Similar to H. pluvialis, Chlamydomonas nivalis is a unicellular green algae with abundant amount of astaxanthin. Its cryotolerant property allows them to live at low temperature and survive on diverse places such as rock, soil, snow, and meltwater. Normally, C. nivalis live surrounded by snow ranging from 0-20 centimetres in depth, however, when the cells are exposed on unshaded snow that may be subjected to intense UV radiation, astaxanthin transforms the green cells to orange or red and acts as a sunshield to protect the algae. Recent reports from various locations from Antarctica to the Himalayas indicate that the increasing frequency of blood snow is one of the indicators of climate change, as an increase in temperature causes snow to melt. The presence of water on snow supported the growth of algae, resulting in the blood snow phenomenon.

Now, what’s your answer?

So, what do you think?

After our long journey from ancient times to the 21st century with the mythologies, stories, and facts laid out, do you think the blood rain and blood snow phenomena are just pure science or is it really a curse? Or better yet, a divine warning or signs urging us to take action against climate change?

Just ‘blood’ for thought.