Explaining the plagues of Egypt: the ten plagues of Egypt, as told in the Book of Exodus, can be easily explained. Or maybe not…

Jeffrey A. Lee

Much of this article is about the plagues of Egypt, as presented in the Old Testament’s Book of Exodus. But this is not a discussion of plagues or of religion; instead it is about scholarship and how it is done when there is a dearth of evidence on a particular topic. Many scholars believe that there is a historical basis for Bible stories and that it is valuable to use the methods of scholarship to shed light on the events these stories describe. The plagues of Egypt serve as one example. This piece is not a thorough review of research on the plagues; I have merely chosen three examples of scholarly research by scientists to illustrate how scholars sometimes hang their conclusions on rather flimsy evidence–and that readers should take this into account as they evaluate scholarly arguments.


There are straightforward explanations of the ten plagues. Most are epidemiological in origin. H.M. Duncan Hoyte (1993) and John S. Marr and Curtis D. Malloy (1996) approach the plagues from a medical point of view, and they do not always come to the same conclusions. According to Hoyte, the water of the Nile turned red because of a “red tide” of dinoflagellates, which is common in salt water, but does occur in flesh water as well. Red tides can be toxic to fish, leading to massive fish kills. In the Nile, the water would have turned red, the fish would then have died, followed by the stench of their carcasses. Frogs would have fled the river, invading the surrounding lands and then died of dehydration. Marr and Malloy also suggest that a dinoflagellate bloom is the cause of color change and the fish kill. The reason for the population explosion of frogs following the fish kill is not clear in their paper (they may have felt that reduced predation by fish was the obvious explanation).

The “lice” of the third plague is sometimes translated as “gnats” and may in fact have been mosquitoes, according to Hoyte. The species is most likely Culex antennatus. Mart and Malloy conclude that nearly microscopic and bloodsucking midges better fit the description of the third plague, particularly Culicoides species.

The flies that constitute the fourth plague are most likely stable flies (Stomoxys calcitrans), according to Hoyte. Marr and Malloy agree that this species is the most likely culprit.

The fifth plague involves a murrain, a plague, that killed many farm animals. Hoyte concluded that surra, a disease that affects most farm animals but not humans, is the cause. Stable flies transmit surra, so plague number four could have led to plague number five. Marr and Malloy conclude that plague three led to plague five, that the Culicoides midge transmitted both African horse sickness (killing horses, donkeys and other equines) and bluetongue (killing cattle, sheep and goats).

The boils and skin sores of the sixth plague, according to Hoyte, resulted from the bites of stable flies. Open wounds led to infections such as Group A streptococci. Marr and Malloy conclude that it most likely was glanders, an airborne bacterial disease of animal and humans presently found in Africa and the Middle East. Fly bites can transmit glanders.

Hoyte simply states that the seventh, eighth, and ninth plagues were a hail storm, a swarm of locusts, and a dust storm respectively. Mart and Malloy point out that hailstorms do occur in Egypt and can devastate crops. A plague of locusts would have devoured all plant food still in the fields. The plague of darkness is a dust storm, a common event in the region.

The final plague, death of all firstborn, is most likely caused by an epidemic of typhoid fever, according to Hoyte. Mart and Malloy disagree with the typhoid idea and offer another explanation. They conclude that the loss of fish, crops, and livestock meant that the only food source left was the stored grains from previous harvests. Toxic substances produced by fungi in the grains could have killed those who ingested them and in a time of shortage, the firstborn would have preferential access to the stored food.


There are straightforward explanations of the ten plagues. Most are related to a volcanic eruption.

Dorothy Vitaliano (1973) takes a geological interpretation of the ten plagues. Most can be tied to the fifteenth century B.c. eruption of Santorini Volcano, in the Aegean Sea. This large eruption is implicated in the destruction of the Minoan civilization on Crete and, as much of Santorini sank below sea level after the eruption, the legend of Atlantis may have a connection to this event. In addition, Vitaliano explains, the eruption’s effects would have been felt further downwind, in Egypt. Volcanic eruptions are known to produce unusual weather conditions and this plays a prominent role in Vitaliano’s explanation of the plagues.

Vitaliano is not sure what caused the waters to turn red. Previous scholars have suggested that some of the ash from the volcano would have been pink and would have washed into the river, thereby tinting the water. Vitaliano thinks that this is unlikely to have been confused with blood and a more reasonable explanation is an algal bloom, which can be red in color. There is a possibility that the algal bloom was connected somehow to the strange weather conditions following the eruption, but she does not speculate about exactly how. With the first plague, Vitaliano is in general agreement with Hoyte and with Mart and Malloy.

The plague of frogs may be attributed to the weather, as well. Some species of desert frogs lay dormant in the soil until sufficient water is available for them to become active and reproduce. They then go dormant again as the land dries out. Heavy rains caused by the eruption could have brought about a massive outpouring of frogs. The third and fourth plagues, lice and flies, can also be explained by unusually wet conditions, conducive to insect reproduction. As a geologist, Vitaliano made no attempt to identify the species involved.

The fifth plague, the death of livestock, may be directly caused by the ash fall. Helda, a volcano in Iceland, erupted in 1947 and again in 1970. Both times, sheep that ate grass covered in fine ash particles died of fluorine poisoning. By analogy, toxic ash may have killed the Egyptian livestock as well. How the Israelite’s livestock survived is not clear, unless they, for some reason, prevented their animals from grazing until the ash had washed off the vegetation. Toxic ash may be responsible also for the skin problems, the sixth plague.

Moving on to the seventh plague, hail, and lightning are often associated with volcanic eruptions. Tiny ash particles can serve as condensation nuclei for hail, and strong electrical charges are common in the ash-filled air.

The plague of locusts may be simply a coincidence, according to Vitaliano. Locust swarms are not unusual in the region and she found no direct connection to the eruption.

Plague number nine–darkness for three days–is easily explained by the ash blotting out the sun. Santorini produced tremendous amounts of ash.

The final plague, death of the firstborn, can be partially explained. Widespread death is a likely aftermath of the insect invasions and crop destruction by hail. Why the firstborn in each family died is not clear.


Vitaliano does make clear that most of her explanation is speculative. She is confident that the ash of Santorini is the explanation for the plague of darkness. In her words (p. 259), “indeed, it is difficult to explain it in any way other than the effects of an ash cloud.” The other explanations are only possibilities.

Hoyte, however, writes with more assurance in his conclusions. He begins his final paragraph with “In summary, the series of disasters was …” followed by a listing of his conclusions. Marr and Malloy do make clear that they are presenting their interpretations of the plagues, “using Occam’s razor as needed to reduce discordant explanations to the simplest and most logical.” I will speculate that Hoyte disagrees that Marr and Malloy’s conclusions are the most logical.

Yet there is no empirical evidence of what happened in Egypt at the time in question, beyond a few passages in the Bible and some Egyptian records that may or may not be related. The scholars I quoted above are presenting logical possibilities, but there is a big difference between possibilities and probabilities. Many people fail to make the distinction between possible and probable, between “could have” and “did” in past events, and between “might” versus “will” in future events. We can see this, for example, in government economic and social policies, archaeology, and education planning. I like to believe that most scholars understand the difference, even if they do not explicitly say so in their writings, but many in the public do not make the distinction.

A second point is that these writers are doing what scholars are supposed to do in attempting to explain the Egyptian plagues. They used their expertise to find what they feel are the best explanations of a particular problem and then presented them to the scholarly community. It is the job of others with relevant expertise to look for flaws in their arguments and present alternative explanations. Scholarship is more about what the community agrees to than about what one person thinks. That there is so little consensus of opinion on the causes of the plagues shows that none of us should be confident in any explanation. Unfortunately, “We just don’t know” is hard for many people–especially experts–to say.

My final point is about thinking critically. I am a geographer, with some background in geology. Many years ago I read Vitaliano’s book and accepted her explanation readily, knowing that it was speculative, but it made sense to me. I now know that I was willing to accept it because I liked the idea that volcanoes have a major effect on civilizations; it made what I do feel more important. When, several years ago, I saw a television program outlining Marr and Malloy’s explanations, my first instinct was to reject what they said because it was fundamentally different from what I had previously accepted. This is an example of lousy critical thinking in a couple ways. I accepted a theory because it made me feel good, not because it was sound and I rejected another theory because it went against my previous learning, not because it was unsound. I like to think that my thinking has matured after recognizing my mistakes.

So what caused the plagues of Egypt? We just don’t know.


Hoyte, H. M. Duncan. 1993. The plagues of Egypt: What killed the animals and the firstborn? The Medical Journal of Australia 158:706-708

Mart, John S. and Curls D. Malloy. 1996. An epidemiological analysis of the ten plagues of Egypt. Caduceus 12:7-24.

Vitaliano, Dorothy B. 197.3. Legends of the Earth: Their Geologic Origins. Bloomington: Indiana University Press.

Jeff Lee is a geographer in the Department of Economics & Geography, Texas Tech University, Lubbock, Texas. He is the author of The Scientific Endeavor: A Primer on Scientific Principles and Practice (2000). E-mail: jeff.lee@ttu.edu.

COPYRIGHT 2004 Committee for the Scientific Investigation of Claims of the Paranormal

COPYRIGHT 2004 Gale Group

You May Also Like

Dr. Scholl’s Steps into Pseudoscience with Magnetic Insoles

Dr. Scholl’s Steps into Pseudoscience with Magnetic Insoles – Brief Article Benjamin Radford Alternative medicine has enjoyed a rem…

Autistic boy killed during exorcism

Autistic boy killed during exorcism – News and Comment Kevin Christopher The Committee for the Scientific Investigation of Claims o…

Fooling and Falling into the Feeling of Being Stared At

Fooling and Falling into the Feeling of Being Stared At – Brief Article David Marks Sheldrake is convinced that his research indica…

The Rorschach Inkblot test fortune tellers, and cold reading

The Rorschach Inkblot test fortune tellers, and cold reading James M. Wood Psychologists have been quarreling over the Rorschach In…