In a new article in the Journal of Insect Science, a group of researchers in Israel shares a simple and creative tool for sampling tree-dwelling insects and arthropods, what they call the tree refuge. Each one is made of a rectangular piece of corrugated cardboard, rolled to form a cylinder, then affixed to a tree trunk or limb with string. (Photos by Jakob Guebel, originally published in Salman et al 2020, Journal of Insect Science)

By Paige Embry

Paige Embry

In the last few years, studies that show significant declines in insects have led to eye-catching headlines. But those studies provide only a small, smudged window into what is actually happening in the insect world, because we simply don’t have enough data to know more.

It’s no surprise. Collecting information on insects and other small arthropods like spiders is time-consuming and expensive. Not only do you need some sort of baseline to which to compare the data, but sampling also needs to be repeated, because population numbers may vacillate wildly from year to year. (See “Insect Declines in the Anthropocene” in the 2020 edition of the Annual Review of Entomology.)

In a paper published March 18 in the Journal of Insect Science, a group of researchers in Israel have come up with one small solution that can help that sampling deficit, at least for trunk-dwelling arthropods: the simple and unassuming “trunk refuge.”

Around the world, a large percentage of global arthropod diversity lives in various microhabitats on trees. Getting the arthropods out of the trees so they can be counted and assessed is done in many ways: beating or vacuuming the trees, fumigation, laying passive traps like light or water traps. These methods don’t work, though, if one of your goals is to collect from a specific microhabitat, like the trunk or upper branches of a tree.

Ibrahim Salman

Ibrahim Salman is a Ph.D. student at Ben-Gurion University of the Negev in Israel and lead author on the new report in the Journal of Insect Science. He writes in an email that some of those sampling methods, like beating or vacuum sampling, “are destructive, time consuming and often not feasible (for example, in fruit trees or vineyards, where plants can be damaged).” In the paper, the Salman and fellow researchers write that the methods available for collecting specifically from the trunk habitat tend to be “expensive, cumbersome to operate, and lethal to the arthropods.”

To solve these problems, the researchers took strips of corrugated cardboard, rolled them into a tube and tied them onto trees with string. “We initially conceived of these devices as arthropod traps,” writes Salman, “but [we] quickly realized that they are actually refugia and sometimes breeding sites.” Ant and beetle fragments found in the refugia showed that what was a refuge for some was a hunting ground for others.

The scientists tested the trunk refugia at both agricultural and natural sites in Israel, leaving the traps out anywhere from a week to about a month. They caught a wide array of arthropods. In just one week, 12 traps placed on oak trees came up with 133 Dermaptera (earwigs), 12 Araneae (true spiders), and a handful of other arthropods.

At one site, the researchers tested three different tube designs and discovered that the arthropods had preferences about their refuges. Blattaria (cockroaches) dominated one tube type, Araneae (true spiders) another, and Hymenoptera (wasps, bees, ants, and sawflies) the third.

The authors note that trunk refugia have numerous benefits. They’re cheap and easy to deploy and pick up. They can be adapted to select for certain arthropod groups. Also, since the refugia collect live arthropods, specific groups can be gathered for rearing or behavioral studies and the unwanted groups released back into the wild. The ease and low cost means that one can easily conduct multiple sampling events per year to monitor for reproduction time or seasonal changes in abundance.

Trunk refugia also seem like they’d be useful in classrooms or for citizen science projects. Salman agrees, writing, “These refugia would be a great way to introduce school children to a diversity of arthropods, as well as to concepts such as arthropod refuges and breeding sites. They can be used anywhere, and even on artificial substrates such as garden walls!”

Paige Embry is a freelance science writer based in Seattle and author of Our Native Bees: North America’s Endangered Pollinators and the Fight to Save Them. Website: www.paigeembry.com.