What’s fieldwork really like? And how do scientists decide where to go and how to search? Field Museum scientist, curator, and millipede expert Petra Sierwald describes a recent expedition.
We went on a collecting trip to Vietnam hoping to find a rich diversity of millipedes, centipedes, and arachnids. Most organism groups have their greatest species diversity in the tropics. But the tropical regions of our planet are also the most poorly known. While mammals and birds are a bit better known, expeditions in tropical regions often yield specimens that belong to undescribed species—ones we didn’t even know existed. For my purposes, targeting millipedes in particular, I traveled with fellow researchers to the pristine forests of northern Vietnam. This area is especially rich in millipede species of the order Polydesmida, which produce cyanide to scare away potential predators.
But where do you start looking for these small creatures? Knowing something about the biology and life habits of these arthropods, we can use a variety of methods to catch them: most millipedes live among their food, which is decomposing leaf litter. So, we rake through leaf litter on the forest floor. Some millipedes consume rotting wood, so turning logs and breaking rotten logs apart often yields specimens. Catching centipedes requires speed—since they’re predators, they move swiftly, often hiding under logs and rocks. Many arachnids also live in leaf litter, and as predators, they’ll typically move swiftly as well. Since a lot of spider species hunt in the vegetation, we use sweep nets and beating sheets to shake them from the branches.
The overarching goal of doing fieldwork like this is to better understand our planet’s biodiversity—meaning, to discover which species live where on Earth. Every species evolved special adaptations to its environment in order to make a living, by securing and using resources in its habitat. Such resource use provides ecosystem services: the organism’s activities contribute to the overall balance of the habitat’s community of plants, animals, and microbes. For example, millipedes chew down the leaf litter and support the nutrient cycling in forest soils. By digging deep into the soil during droughts and cold temperatures, millipedes create tunnels for air and water to percolate through the soil.
We examine the characters of as many different species in a group we can find. Using these features, which include molecular, morphological, behavioral and other characters, we assemble a “tree of life.” This shows us which species are related to each other and how their characters changed through evolutionary time.
The sheer number of different arthropod species—over one million described species and many more to be discovered!—is one of the most astounding phenomena of life on our planet. Each species is different, with slightly different lifestyles and adaptations to some particular resources in the habitat. Sure, arthropod specimens are small, but what they lack in body size, they make up for in abundance.
Video produced by Greg Mercer and Laurel Tilton.