David C. Houghton is Professor and Chair of Biology and the Director of the G.H. Gordon Biological Station. His research focuses on caddisflies. Courtesy | David Houghton

What is it that first got you interested in this research?

I have always loved being out in nature, whether hunting, fishing, hiking, paddling, or just chasing frogs around. I went to college to study natural resources and realized I particularly loved poking around in streams and rivers. It soon became apparent that there was a whole underwater world of aquatic insects that was fascinating and needed to be studied.

What is the most fascinating feature of caddisflies?

Caddisfly larvae have glands in their mouthparts that produce a sticky silk, much like a spider. They use that silk to glue together sand, small rocks, sticks, and other debris to construct portable cases. If you’ve ever seen a small pile of sticks or a tube of sand walking around on a stream bottom, that’s a caddisfly.

Ecologically, caddisflies are important because they process organic matter in rivers, thus cleaning the water. They also are important links in the food web, especially for trout and other sport fish.

On a practical level, caddisflies are highly indicative of stream conditions. So, by quantifying caddisfly populations, we can assess the biotic integrity of rivers and their surrounding watersheds. So, I’m not just studying biodiversity for its own sake, but also for what it can tell us about the surrounding environments, which ultimately affects people as well.

What is unique about your study of caddisflies?

The vast majority of scientists who use caddisflies to assess river health focus on the underwater larval stage. We are one of the only labs to use the winged adult stage instead. There are some major advantages to doing so, most notably the ability to sample all stream habitats representatively.

Why do you think this form of study is important?

Whether you call it environmentalism or creation care (or both!), the conservation of organisms and their habitats is a fundamental human imperative. While people focus on the big furry critters, insects are disappearing at unprecedented rates. Based on large-scale habitat modeling, nearly 60% of stream segments in the Upper Midwest have lost at least half of their original caddisfly biodiversity. That’s an enormous loss of both species diversity and the ecological services provided by those organisms, and it is both a moral and an existential problem that we should take seriously.

Hillsdale College has a caddisfly collection of over 300,000 species. How much effort and how many years does it take to build up that level of collection and information?

The Michigan work began in earnest in 2010 after I assumed directorship of the college’s GH Gordon BioStation in northern Lower Michigan. At first it was just two students and I cruising around northern Michigan sampling any streams that we came across. Then we expanded to the Upper Peninsula in 2011, then Indiana and Wisconsin in subsequent years, and so on. The collection just crossed the 400,000-specimen threshold. So, to answer the question: 14 years of several faculty and a whole lot of students all working together.

Moreover, combined with the 250,000 specimens that I collected while at the University of Minnesota and another 150,000 from a collaboration with the Illinois Natural History survey, our caddisfly database contains data associated with around 800,000 specimens collected from nearly 5000 sites in Iowa, Illinous, Indiana, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, Sout Dakota, and Wisconsin, making Hillsdale College pretty much the center of caddisfly research in the Upper Midwest.

Do your studies of thermal tolerance of aquatic ecology lead to simply deeper understanding of species or is it meant to lead to actions being taken?

A little bit of both. Scientists have a decent understanding of how climate change will affect terrestrial organisms, but comparatively little on aquatic organisms like caddisflies. Many streams are buffered by groundwater, so temperature increases will probably be less severe than on land. But, because of that groundwater buffering, many aquatic species have evolved to exist only within a very narrow temperature range. Learning that range and identifying which species are particularly susceptible to thermal pollution is important from both scientific and policy standpoints.

What is your newest focus or most recent developments in your research?

I was on sabbatical in Quebec during summer and fall 2023, focusing on the caddisflies of the Laurentian Mountains. As luck would have it, I was there for the worst wildfire season on record. While all of the fire and smoke made collecting difficult, I now have caddisfly data from right after a catastrophic natural disturbance, and it will be really interesting to see how the rivers recover over the upcoming years.

Also, two of my students (Hannah Allen and Christina Manna) had research fellowships at the University of Nebraska last summer. Both sampled caddisflies while they were out there, and collectively they found over 40 caddisfly species that have never been found in that state before. It just goes to show that you don’t have to travel to exotic locations halfway around the world to make new discoveries.

Are students involved in your research? If so, how are they involved?

Definitely — there is no way that I could do this work without them. I have students studying caddisflies for their own capstone senior thesis projects. As mentioned, I have students sampling caddisflies in various places around the US and students working in the sequencer lab doing DNA barcoding. I typically hire 5-10 students per year to help me out with sample sorting in my lab. And, I occasionally offer an internship on museum and database techniques where students can learn by working with my specimens.

How can students get involved and would you encourage them to do so?

Yes, please! I can only be at one place at a time, so having an army of students sampling on my behalf is highly appreciated. Collecting caddisflies is easy and I can show someone how to do it in about 15 minutes. If anyone is interested in doing some sampling at home this summer, please email me at dhoughton@hillsdale.edu and I will set you up with equipment. Who knows what cool critters you might find.

What are the most important takeaways from your research? Or, what impact do you wish it to have?

Mostly I want people to realize and appreciate the importance of the natural world, including the creepy-crawly things. Aquatic insects like caddisflies are some of the unsung heroes of nature. Much like oceanic phytoplankton producing atmospheric oxygen or lowly little midges pollinating chocolate plants, caddisflies are engaging in activities every day that ultimately benefit people. Next time that you’re sitting by a trickling stream with crystal clear water, thank the caddisflies. And if you see one, bring it to me instead of squashing it.