In the forests of Massachusetts, scientists have stumbled upon a ragtag gang of strange “giant viruses” that were previously unknown to science.

Biologists at the University of Massachusetts Amherst discovered 16 new giant virus species by accident while carrying out an unrelated study on the effect of soil warming on microbes. The discovery is quite unusual because the majority of giant viruses have previously been discovered in aquatic habitats. Finding a bunch of new ones in an inland earthy forest environment suggests that these unusual critters are perhaps more ubiquitous and diverse than previously thought.

“Our research is usually focused on the effects of soil warming, but this new mini-metagenomic approach has uncovered a trove of viral and bacterial biodiversity in species groups we don’t typically associate with the soil,” Jeff Blanchard, study author and biologist, said in a statement.

“There are a number of mysteries we’ll be following up on.”

So, just how giant is a giant virus? Typically, viruses are hundreds of times smaller than bacteria, making them some of the smallest known life forms. Giant viruses can be larger than bacteria, however, the "giant" part of their nickname actually refers to the size of their genomes, which are notably larger than those of other viruses.

They are especially strange because they contain many unique genes that aren’t found in other life forms. A handful of scientists have controversially suggested that they actually represent a distinct supergroup and a “fourth domain” of life, along with Archaea, Bacteria, and Eukarya, however that idea is not widely accepted.

Writing in the journal Nature Communications, the researchers explain this gang of giant viruses was discovered in the soil of Harvard Forest in Petersham, Massachusetts. In parts of this forest-come-laboratory, scientists placed heating cables similar to those used to keep football and soccer fields from freezing just under the soil in order to study how climate change might affect soil and microbial life.

The discovery came about thanks to a technique known as mini-metagenomics. They took a mere spoonful of soil from this lightly heated area and carried out “deep sequencing”, which gathered the DNA of approximately 2,000 individual cells in the sample, including these 16 mysterious giant viruses – “a wonderful surprise and very exciting new science,” according to Blanchard.

“Not only did we just discover many new giant viruses, but we did it using a thimbleful of soil. It would be nice to characterize these viruses one at a time, there’s a lot of skill and art in that," he added. "Finding 16 at once is kind of overwhelming, and none of them are the same. If you think of all the soil in the world, if there are 10,000 species of bacteria in a gram of soil, about a teaspoon, imagine how many new giant viruses are out there.”