Sorting Arthropods for Identification

Part of the Biodiversity Counts Curriculum Collection.

When we asked Kefyn Catley how he thinks students should go about identifying their arthropod specimens, he said, "That's the 64,000-dollar question." 

Identifying arthropods is a challenge, even to Kefyn, who spends his days identifying Australian ground spiders at the American Museum of Natural History. He also writes identification keys, which are used to classify specimens down to the species level. This sort of work is called systematics

"Systematics deals with species," Kefyn explained. "The unit we study is the species, not populations or individual organisms." But identifying an organism to species can be very difficult, he said, even for experienced scientists. Kefyn thinks it is more realistic for students to group arthropods by order and try to identify them further by families.
Kefyn recommends putting everything that has been collected into alcohol, except butterflies and moths. Most will be dried and pinned later on, but soft-bodied specimens, such as spiders and caterpillars, must be kept in alcohol, he told us. Then the sorting can begin.

How to identify arthropods

Identification involves a series of steps, Kefyn explained. "Systematists begin with the largest classification—the phylum Arthropoda—and keep narrowing it down—through subphyla, class, order, family, genus, until they get to species. You may not get as far, but the procedure is the same," he said.
"Start by making a very gross first cut: separating things with wings from things without wings. Next divide those into very basic groups: beetles, ants, flies, wasps, for example," he said. Do not be surprised if you have a lot of beetles, Kefyn mentioned as an aside, since beetles are the largest group of organisms on the planet.
He advised using a picture key such as is found in many field guides or asking a local museum or naturalist to recommend a key to arthropods most likely to be found in your area. When you use such a key, you will be sorting according to appearance, or morphospecies.
"Basically, you're eyeballing your specimens, looking at the differences and similarities. Sort your specimens according to shape, color, number of legs, and any other differences you can discover, and see how many groupings (what scientists call taxa) you come up with and how far you can take it," he suggested.


 "If you are able, for example, sort all the things that appear to be beetles. Next separate the long, narrow beetles from the round beetles. Then take a closer look at the long, narrow beetles and see characteristics that some share, like the same type of antennae or the shape of their wing covers. This is the type of process of elimination that scientists use all the time to group organisms. In doing so, you may be sorting beetles into families, or even genera, without knowing it. This first step can take place by just using your powers of observation—you don't even need a key," he said.
"Some students may want to specialize in a particular group," Kefyn suggested. "Some might want to tackle the bees, others might take on the ants. That way you'll end up with experts in the class who can share their knowledge with others, which is what entomologists do all the time."

About Kefyn Catley

If he had not been seduced by his childhood love of collecting living things, Kefyn Catley might still be a professional musician.

Kefyn Catley

As a boy growing up in Wales, Kefyn remembers being "one of those kids who were always poking under stones and looking into walls. I was fascinated by what I found there. I collected beetles, moths, birds' nests, birds' eggs. I had hundreds of birds' eggs, but the bugs were always more important to me.

"I was really, really young—under five—when I got one of those little magnifying things that you can put a bug in and look at it. Then, when I was six or seven, my older sister bought me a microscope, and that was it. I was hooked."

Except, Kefyn told us, he took a rather long detour, and it was nearly 30 years before he came back to his first love.

"I didn't have much of a choice when I was school age. I really wasn't all that good academically at the things that mattered, so I went into music." He studied flute and other woodwind instruments, then got a job playing in a symphony orchestra and teaching.

"After I'd been working as a professional musician for about 20 years, I got to know some people in the neighborhood where I lived who were bug maniacs, just like I had been when I was younger. We started going out every weekend collecting all sorts of bugs, spiders, and stuff, and I found myself spending more time doing that than my music.

"It came to the point that I had to make a decision: Was I going to stay with music as a profession, or was I going to go into science proper, which is what I always wanted to do when I was younger?"

Kefyn chose science.

"I was in my thirties, and it took me ten years to change careers. I had an arts degree and I needed a science degree. That led to a master's, which led to a Ph.D."

Now he is a National Science Foundation Research Fellow working in the Entomology Department at the American Museum of Natural History. His specialty is the identification and classification of Australian ground spiders.

Is he glad he made the change? Kefyn answers with an enthusiastic "Yes!" He never got over his childhood fascination with arthropods, and he is happy to have the chance to study them every day. But it is not a matter of studying "what's out there," he argues.

"Where's out there? It's really here," he insists. "It's not some place you go to look at nature. We're all in this together, all completely interdependent. I think it's important to understand our own position in the world, to get the big picture. And that's something bugs help us do really quickly."