by James B. Nardi
Princeton University Press, 2023
If you want to explore new frontiers, look no farther than the nearest forest. Each tree, from roots to branches, is home to its own complex and minute ecosystems. James Nardi’s The Hidden Company That Trees Keep is a guidebook to this overlooked world of cryptic insects, diverse parasitoids, and other odd and tiny animals. Any good guidebook includes maps, and Nardi, a skilled artist as well as author and biologist, has provided three. Each is a beautiful, two-page color plate depicting a major territory within a tree: the leaf-, bark-, and rootscapes.
Nardi has likewise organized most of the chapters by location on the tree, moving from crown to ground. Within a chapter, he often introduces a broad topic (for example, “the many ways to prepare and eat leaves”) and then offers short biographies of numerous creatures relevant to that topic. Nearly every page includes grayscale portraits of the characters that Nardi describes in the text, often with intriguing names such as “sparkling archaic sun moths” or “stiletto flies.”
In chapter 1, Nardi introduces the staggering complexity of interconnected and tiny lives that rely on different areas across the tree. Starting at the molecular level, he explains how trees respond biochemically to their many companions and introduces categories of those companions, including “invertebrate allies: parasites and predators” and “endophytes: symbiotic microbes belowground and aboveground.”
Chapters 2 and 5 focus on the canopy, touring leaves and twigs, and on flowers. Nardi explains the varied ways that insects make themselves at home, and sometimes also treat that home as dinner. Not only are there many ways to eat a leaf, but there are also many ways to convert a leaf into a shelter, from simple leaf rolling to sophisticated gall making. Many of the juvenile insects that appeared in earlier chapters return in chapter 5 as adult pollinators, giving back to the tree in reproductive support what they took as food during their larval stage.
In chapters 3 and 4, Nardi reveals how the trunk of a tree offers food and shelter in two primary ways. A huge variety of tiny creatures are active on the surface of the bark, and many specialize in tapping tree sap for its sugar, amino acids, and minerals. All these creatures have allies and parasitoids of their own. Below the surface, but just as uniquely adapted and interconnected, are the insects that live inside the tree, feeding on wood, fungi, or other arthropods as they tunnel between bark and heartwood.
In chapter 6, Nardi explores the realm of soil beneath a tree – home to decomposers and root feeders – and their predators and parasites. Alongside familiar insects such as cicadas and fireflies, bizarre and overlooked groups of arthropods, including the coneheads and two-pronged bristletails, take central roles in the webs of underground interactions.
Nardi ends with advice on how we can visit these miniature landscapes. Chapter 7 includes diagrams and descriptions for how to safely collect, keep, and observe the hidden companions of trees, whether you want to attract insects to a light or look more closely at small life forms under a microscope.
There is so much detail to enjoy at every level of this book, from Nardi’s drawing of the textured wings of a lace bug to his descriptions of the layers of connections between trees, herbivores, parasitoids, and predators. He invites readers to appreciate the complexity we can see all around us, if we simply take a little time and effort to look. So, to all the observant explorers out there: grab this guidebook. Entire worlds are in trees, waiting for you to visit.