In A Plague of Frogs, William Souder confronts an ecological emergency from both a scientific and a political perspective. He demonstrates the complexity of solving any environmental problem through personal accounts with the scientists and government agency workers involved. A Plague of Frogs is a case study on how organisms interact with their biotic and abiotic environment. Frogs are particularly vulnerable to contaminants in their habitats because they spend the most pivotal stage of their development fully emerged in the water for months. Souder describes frogs as a “sentinel species,” meaning that the effects of contaminated water manifest more quickly in their bodies than in humans. “Sentinel species” are generally regarded as nature’s warning sign that something in the wild has shifted. When a group of students on a field trip to Nicollet County, Minnesota in the summer of 1995 discovers hundreds of deformed leopard frogs – frogs with extra limbs, missing limbs, and skin webbings – this raises red flags for scientists and government agencies throughout the state. A Plague of Frogs follows those involved in identifying the causes of the deformities.

Leopard frogs are the main species examined throughout Souder’s work. The leopard frog is a prime subject because it is a multiphasic and migratory amphibian. Leopard frogs have two different living spaces: breeding sites and overwintering sites. The overwintering sites are where frog tadpoles spend months at the bottom of rivers not quite frozen solid before they emerge in the spring to metamorphose. This is the place where developing frogs absorb the most pollutants.

Two main causes of deformities are identified by Souder: chemicals and parasites. Souder explains the issues toxicologists face when trying to identify a chemical contaminant. Farmers use over a dozen different chemicals on their fields in a single year. Often the pesticides and herbicides used in agriculture are made to break down quickly, so by the time these compounds enter the water they are mixed into what Souder calls a “chemical soup.” For these reasons, identifying on single chemical is difficult if not impossible. The reason chemical pollutants affect a frog’s development lies in the compounds’ mimicking of retinoic acid. Retinoic acid helps in development by differentiating cells. Too much of the acid causes extra limbs to grow, but too little of it inhibits limb growth. Oullet, a biologist from Canada, gains credibility for his collection of nearly half a million frogs from the St. Lawrence River Valley. His experiments confirm the role of pesticides in limb deformities.

One of the primary sites discussed is an undisturbed lake on the Bock property near Alexandria, Minnesota. The lake is described as undisturbed, as there was no previous field runoff from agriculture. This alone proves that pesticides could not explain all of the deformities. Hoppe is the primary investigator of Bock’s lake. He discovers the relationship between a frog’s proximity with water and the extremeness of its deformities. More aquatic species, like the rare mink frog, have more dramatic deformities in higher ratios than less aquatic species like the tree frog. This indicates that the cause of the deformities must be in the water.

Parasites affect amphibians by creating cysts in the limb buds. These cysts intercept DNA messages during development, leading to the growth of extra limbs. This theory is supported by Stan Session’s research on trematodes and the parasite Ribeiroia. However, Souder points out that while parasites may explain some cases of extra limbs, this theory leaves out the major type of deformity: missing limbs. Souder and many of the scientists he works with come to the conclusion that the deformities are not caused by just one factor, but by many factors working together to change the frog’s natural habitat.

Souder makes the important distinction that the scientific community is not a group effort, but a culmination of individual efforts. This is evident in the frequent arguments between the biologists, herpetologists, and toxicologists. Sessions, who published reports on the effects of parasites on limb development, is generally disliked by the scientific community. His arrogant nature and stubborn conviction, an unusual personality for a scientist, leads many researchers, including Oullet, to write off his theory. Souder reiterates several times that academics do not get along very well with government agencies. Meetings between the two groups demonstrate the clash between them. The academics frequently express their thoughts that government agencies does not understand the scientific implications of the issue and are not doing anything to solve it. Government agencies have limits; they simply cannot devote all of their employees and all of their funding to investigating the frog deformities. Although there is this clash, the academics and the government agencies need each other to solve ecological issues. The academics provide data from field work to help the government agencies decide what potential cause to invest in or whether to invest in the issue at all.

This novel shows the dramatic ways in which humans can change and destroy an ecosystem that survived, unchanging, for hundreds of thousands of years. Through the heavy use of chemicals in agriculture, natural habitats can be poisoned. This relates to topics discussed in Physical Geography, such as the water and nitrogen cycles, and how these are interrupted and changed by the presence of humans.

Souder handles a technical subject matter with descriptive and often artful prose. He approaches the scientific aspect in an elementary manner, providing simple examples to explain complicated biological processes and terms. This allows a reader with no scientific background to be confident in his or her understanding of the material. However, this approach may irritate a reader with substantial knowledge in the field who does not need scientific processes “dumbed down.” Souder’s writing style is very informal, often featuring fragments of sentences to show emphasis. Overall, his narrative is a refreshing, casual take on the scientific and political aspects of biology.