Recently, we had the opportunity to sit down with Dr. David Costello to talk earthworms, research, and invasivory. 

Can you start by giving us a quick overview of your dissertation research?

My dissertation research focused on how the impact of invasive species can extend outside the typical boundaries of an ecosystem.  For example, invasive earthworms are typically thought of as a terrestrial problem, but my research showed that the way earthworms change nutrient cycling can cause excess nitrogen to enter adjacent streams.  In general, I found that if you are trying to manage invasive species in an ecosystem, you need to be aware of what is going on in the surrounding areas, even if they are completely different ecosystems.

When did you first become interested in invasive species research?

As an undergraduate at Hobart College, I got my first exposure to invasive species during a summer research internship after my sophomore year.  We conducted a survey of Seneca Lake trying to correlate zebra and quagga mussel densities to lake characteristics.  I spent the following semester studying biology abroad in Australia where the imprint of invasive species, like European rabbits, is really severe.  Both of these experiences sparked my interest in invasive species issues and research in general.

Returning to your dissertation research- have you eaten earthworms?  How did you cook them?  Can you describe your first bite?

I have eaten earthworms a couple times.  In my experience, I’ve had some success blanching them before battering in flour and deep-frying.  It is tough to get earthworms completely clean so I would describe my first bite as “gritty”.  If you can get all the dirt out of them, I think earthworms wouldn’t taste too bad.  For now, I’ll stick to gummy worms!  (Editor’s note: check out some tips on preparing earthworms here)

Dr. Costello samples a deep-fried earthworm

Do you have any other eating invasive species experiences you’d like to share?

I really enjoyed eating rusty crayfish while doing my graduate work at the University of Notre Dame Environmental Research Center in the upper peninsula of Michigan.  My favorite cooking technique involved simply throwing them on the grill and letting them steam in their own shell (technically, an exoskeleton).  It gave them a nice smoky flavor and the meat was still pretty juicy.

What have you been working on since you graduated?

I am currently a postdoctoral research fellow at the Cooperative Institute for Limnology and Ecosystem Research (CILER) at the University of Michigan.  For now I am taking a break from invasive species and working almost exclusively on chemical pollution.  I am working on a number of projects that focus on metal contamination in sediments, which is often the last thing to be cleaned up after a mine or industrial plant closes.  We are exploring the chemical and physical process that cause metal buried just below the surface to be released and how this can potentially affect organisms living on the bottom of aquatic ecosystems.  Invasive earthworms are not far from my mind and I am looking forward to resuming that research.

Any plans to eat any of your study organisms in the future?

I think it is a fun idea as long as your study organism isn’t endangered or poisonous.  I don’t have any specific study organisms right now but for any new projects in the future that will definitely be a consideration!

I guess I’ll go eat worms!

We should begin by admitting that, just like our adventures in garlic mustard ice cream, we’ve made several attempts at cooking invasive earthworms with limited success.  We can offer a few tips on collection and preparation though, and we hope that some of our more daring readers will experiment with some recipes and report back to us!  One great guide to getting started we’ve found is “Entertaining with Insects” by Ronald L. Taylor and Barbara J. Carter which has a great appendix on collecting and preparing earthworms (which the authors admit are not insects).  Here, we summarize their tips as well as some of our own experiences on worm collection and preparation.

Collection

If you’ve been outdoors in a rain storm, then you know earthworms can be easy to collect because they come up out of the ground when it gets too wet.  If you’re looking to satisfy your worm craving in dry weather, you can use a garden hose to simulate rainfall on a small patch of land.  To further enhance your worm hunt, you can sprinkle mustard powder on the ground before you start watering- the mustard powder acts as an irritant to the worms’ skin and will encourage them to come to the surface more quickly.

At invasivore.org, we can’t stress often enough the importance of knowing the history of the area in which you are hunting and foraging.  Earthworms spend their entire lives eating decaying material in the ground, so be sure not to collect from areas with a history of pollution, pesticides, or other chemical treatments you wouldn’t want to ingest.

Preparation

The old adage, “you are what you eat” applies throughout the animal kingdom, and since earthworms essentially eat dirt, you will want to purge their guts before eating them.  We have found that earthworms will live for at least several days in cool conditions in moist flour or cornmeal while replacing the dirt in their guts with something more palatable.  “Entertaining with Insects” reports that earthworms eat and excrete their weight every 24 hours, so a day or two of purging should be plenty.

When you’re ready to cook, “Entertaining with Insects” recommends boiling earthworms for 10 minutes before adding them to your recipe.  We’ve had some success simply breading and deep-frying earthworms, but earthworms may also be an excellent ingredient in stews, pastas, and even omelets.  What recipes will you come up with?

Contributor David Costello enjoys a deep fried earthworm

In our weekly roundups, we present the latest eating invasive species news from around the web.

First, we are thrilled to be included among some top resources for eating invasive species in Conservation Magazine!

We learned about an upcoming snakehead dinner benefiting oyster recovery efforts in the US Northeast.

Coincidentally,we weren’t the only site to profile invasive earthworms this week- check out Great Lakes Echo for more great information!  Also, invasive earthworms appear to be turning the tables on early (native) birds in North America.

Chef Philippe Parola aims to change minds about eating Asian carp.  Maybe people should try the Asian carp chorizo being cooked up at Purdue?

Popular Mechanics reports on eating lionfish.

They’re also starting to eat invasive flathead catfish in Florida.

And also in Florida, our old friend Wynne Parry at LiveScience urges you not to release pets into the wild.

Finally, on the other coast, Entomologists in California search for natural invasivores.

Miles of ice and cold temperatures during the last glaciation (~10,000 years ago) made Canada and the Northern US completely inhospitable to earthworms.  Earthworms naturally disperse at a very slow rate (max 10 m/year), and native worms that were confined to the southern US have not moved very far north.  What we find now in the previously glacier-covered lands are European species of earthworms transported to North America by humans.  Most likely, European worms arrived here through soil used for ships’ ballast or among the roots of plants moved to the new world.  Once established in North America, people continued to move worms to new areas both intentionally and involuntarily with plants, in soil, and in clods of dirt stuck to tire treads and horse hooves.

One common earthworm, the European nightcrawler Lumbricus terrestris. Photo credit: Wikimedia Commons

After the glaciers receded from North America, a very unique forest community developed.  With no large-bodied decomposers, thick layers of leaf litter (called duff) accumulated and plant and animal species took advantage of this new habitat.  When European earthworms encounter these previously earthworm free forests, they chew through the thick litter rapidly with devastating effects on the forest floor.  By consuming the duff layer, earthworms alter nutrient cycling, expose bare soil to erosion, and reduce populations of plants and animals using the thick litter layer as habitat.  The effects of European earthworms are most apparent in parts of Northern Minnesota where the populations of invasive earthworms advance through forests like an invading army creating a striking visual of bare soil where the earthworms have been and thick litter layers soon to be consumed by the worms.  Furthermore, the rare goblin fern is threatened with extinction by invasive earthworms.

Although the presence of invasive earthworms in certain forests is devastating, the story of whether earthworms are good or bad isn’t simple.  Like some other invasive species (e.g., Pacific salmon in the Great Lakes) we do get some benefit from these foreign worms.  In agricultural fields and gardens without leaf litter, the mixing of soil by earthworms actually improves soil porosity and fertility.  Like many other invasives, once worms move from the garden to the forest there is no way to remove them.  So the best we can do is slow the invasion by being careful with how we handle soil, plants, compost, and bait buckets that contain earthworms.  The story of invasive earthworms doesn’t end here because new earthworms from Asia are being discovered in North America and early evidence shows that these worms are even more voracious feeders than their European brethren.  So remember to contain those crawlers!

This guest contribution comes to us from Dr. David Costello, a research fellow at the Cooperative Institute for Limnology and Ecosystems Research at the University of Michigan.  Dr. Costello earned his B.S. in Biology from Hobart College and his Ph.D. in Biology at the University of Notre Dame.  Currently, his research focuses on how invasive species and chemical contaminants affect the structure and function of ecosystems.