Eric R. Larson
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ericrlarson.bsky.social
Eric R. Larson
@ericrlarson.bsky.social
2.6K followers 4.8K following 150 posts
Associate professor in freshwater ecology, University of Illinois at Urbana-Champaign. Crayfish, invasive species, environmental DNA, and more. https://publish.illinois.edu/erlarson/
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ericrlarson.bsky.social
This is another of our studies that I really value for getting us out to the same streams throughout the year, with a snapshot here of a few of our fall and winter sampling events.
Three stream sites as columns over five sampling events as rows from fall (top) through mid-winter (bottom), taken from bridge crossings looking upstream. The stream in the left column is adjoined primarily by row crop fields with a wood lot in the distance. The stream in the middle column has an intact riparian buffer with leaves changing color at the top rows through absent in the bottom rows. The stream in the right column is the largest and is neighbored by dense riparian forest with a ridgeline visible in the middle distance.
January 12, 2026 at 4:54 PM
ericrlarson.bsky.social
Do precipitation events have opposing effects on aquatic versus terrestrial environmental DNA (eDNA) recovered from streams and rivers? New from the lab at Ecological Applications: doi.org/10.1002/eap....
Linear mixed model predictions for aquatic (blue solid) and terrestrial taxa richness (brown dotted) in response to (A) rainfall (in centimeters) and (B) water temperature (in degrees Celsius) with 95% CIs.
January 12, 2026 at 4:48 PM
ericrlarson.bsky.social
Semi-related: this signal crayfish from G.C. Miller's 1960s thesis (The Taxonomy and Certain Biological Aspects of the Crayfish of Oregon and Washington), covered in barnacles out of the Columbia River estuary at Astoria.
A black and white image of a signal crayfish (Pacifastacus leniusculus) seen from the side or lateral view with barnacles covering ~50% of its carapace.
December 21, 2025 at 8:27 PM
ericrlarson.bsky.social
The Sangamon River of Illinois through the seasons. We visited this site every few weeks in 2025 to track changing stream communities with environmental DNA.
A red covered bridge over a river in winter with shallow snow on both banks and thin, clear ice covering most of the surface of the water A red covered bridge seen from a river bank in early spring, with silver maple trees beginning to leaf out. The river is turbid, with sycamores visible on the far bank. A red covered bridge seen from mid-channel of a turbid river in mid-summer, with forest on both banks A red covered bridge in late fall with drifts of slush on its roof, seen from mid-channel of a wadeable river. Most trees have lost their leaves.
December 6, 2025 at 2:51 PM
ericrlarson.bsky.social
New OA study led by Dr. Caitlin Bloomer of U. Illinois: can you predict good habitat for burrowing crayfish even if your model is trained on data from different burrowing crayfish species (doi.org/10.1111/fwb....)? Highly relevant to these hard-to-detect and identify animals.
Two crayfish burrows seen from above or plan view Two crayfish burrows seen from the side at an angle, where one burrow is about three times taller than its neighbor. The burrows are in surprisingly coarse or sandy substrate, with some fine, gray to orange pebble noticeable in the taller burrow.
December 4, 2025 at 5:02 PM
ericrlarson.bsky.social
I know this result is a bit obvious, but I think it merits evidencing: if you remove all vegetation from miles of natural streams, there are costs to wildlife and to people who enjoy and benefit from that wildlife. If you hunt or fish or bird watch or hike, we live in a diminshed landscape.
A wadeable, second order stream in downstate Illinois that has recently had all riparian vegtation removed from one bank, where three researchers stand looking at the stream. The opposing bank retains a small block of forest in early spring, with invasive honeysuckle beginning to leaf out. A row crop field is visible in the middle distance below a blue sky with scattered clouds.
December 3, 2025 at 4:56 PM
ericrlarson.bsky.social
Riparian buffers help more than just streams and rivers in agricultural landscapes. Lab Masters student Olivia Reves used environmental DNA (eDNA) to quantify the benefit of riparian buffers to terrestrial wildlife in downstate Illinois; open access at doi.org/10.1111/1365...
A figure showing a stream without a forested riparian buffer in the top panel and a stream with a forested riparian buffer in the bottom panel. A cartoon water bottle with a DNA symbol in each water bottle directs to adjacent insets with silouttes of representative wildlife at each stream, with the forested stream having more species and including amphibians, reptiles, bats, and flying squirrels.
December 3, 2025 at 3:06 PM
ericrlarson.bsky.social
New invasion note from southern Idaho, where we've rediscovered the non-native red swamp crayfish after a half century without detection (doi.org/10.3391/bir....). Intensive burrowing by red swamp crayfish could be a risk to canals and other irrigation infrastructure.
An irrigation ditch centered in the image that has dried to a single, isolated pool in the foreground. There are grassy banks on either side of the ditch, with two men standing on the right bank in an orange sweatshirt and blue shirt.
November 10, 2025 at 5:04 PM
ericrlarson.bsky.social
New faculty position in the University of Illinois Department of Natural Resources and Environmental Sciences for an assistant or associate professor of agroecology: illinois.csod.com/ux/ats/caree.... Position closes October 31st. Happy to answer questions about the dept / university / town.
A prairie with a wetland in the middle distance and a tree line on the horizon under low, scattered clouds
September 24, 2025 at 9:29 PM
ericrlarson.bsky.social
Completed my annual trip to northern Wisconsin, continuing population monitoring of invasive rusty crayfish (Faxonius rusticus) that extends back to the 1970s. Populations remain down, at only ~25% of past peak abundances, with surprising catches of large native snails in our traps.
A slightly out of focus rusty crayfish (Faxonius rusticus) held between a thumb and forefinger with the calm surface of a lake in the background Two boats docked in the foreground of a large lake with a yellow floating platform in the middle distance and a forested shoreline ~2 miles back on the horizon Sunset on a large, calm lake as a band of orange below emerging stars A square white bucket with ~16-20 rusty crayfish (Faxonius rusticus) waiting to be counted and measured
September 6, 2025 at 3:00 PM
ericrlarson.bsky.social
This pool was packed with non-native virile crayfish; we recovered >120 in only four traps. It will likely dry out by the end of summer, but virile crayfish have dispersed through this intermittent reach. We found them abundant in the permanent stream higher up the watershed (photos 2 & 3).
An olive brown crayfish held between a thumb and finger with a drying stream pool out of focus in the background. A small but rocky stream below a blue sky, flowing through sagebrush steppe. A view from a bridge crossing down into a stream bed of cobble and fine sediments, where one crayfish is visible crawling on a rock.
August 20, 2025 at 9:24 PM
ericrlarson.bsky.social
So ... any crayfish in this small and declining habitat?
A drying stream pool above a culvert, with a researcher collecting crayfish traps. Five gallon buckets, crayfish traps, and a clipboard are visible on the stream bank.
August 19, 2025 at 3:48 PM
ericrlarson.bsky.social
Our search for invasive crayfish barriers includes more than just dams or irrigation diversions. Because the virile crayfish is intolerant of stream drying (doi.org/10.1086/725318), intermittent reaches could present barriers to upstream spread to permanent streams in the mountains.
An isolated stream pool above a culvert (not visible, where the photographer is standing) with a dry bed upstream. The pool is turbid and surrounded by dry steppe, with mountains visible in the distance under a mostly sunny sky.
August 19, 2025 at 3:46 PM
ericrlarson.bsky.social
Crayfishing.
Two researchers hold a seine downstream of them in a moderately wide, rocky river Two researchers check hand nets while overturning rocks on the shoreline of a reservoir Two researchers check dip nets along the shore of a stream impounded behind an irrigation diversion
August 12, 2025 at 10:50 AM
ericrlarson.bsky.social
Here an abundance of crayfish claws and carapaces have been cleaned out of center pivot irrigation filters that had clogged. In our study region, many farmers and ranchers identify this as a problem, but I don't think anyone has quantified these type of impacts of invasive crayfish to agriculture.
A pile of debris on grass that features many obvious crayfish claws and carapaces, cleared from a filter on center pivot irrigation that had clogged
August 8, 2025 at 9:38 PM
ericrlarson.bsky.social
The non-native virile crayfish (Faxonius virilis) in particular has boomed in regions of the western US without any native crayfishes like the Colorado River (nas.er.usgs.gov/queries/Fact...). Given its abundance in irrigated lands, I wonder if we're missing damages and costs as an ag pest?
A map from the United States Geological Survey's nonindigenous aquatic species database showing the native range of the virile crayfish (Faxonius virilis) as light brown and non-native watersheds as a dark red. The species has a broad native range spanning the Great Plains, upper Mississippi River, and Great Lakes basin, but now occurs as a non-native species west of the continental divide and in Atlantic-draining watersheds of Appalachia. It's probably the most widespread non-native crayfish in North America, but is minimally studied relative to invasive crayfishes with more global distributions like the red swamp crayfish (Procambarus clarkii).
August 8, 2025 at 5:32 PM
ericrlarson.bsky.social
I routinely get calls from water management districts in southern Idaho concerned about damage to canals from burrowing by this same non-native crayfish. In estimates of economic costs of invasive crayfish (doi.org/10.1016/j.sc...), I think we're missing effects on agriculture in the western US.
An irrigation diversion with sloughing banks that, on closer inspection, were full of crayfish burrows. Mountains and patchy clouds are visible in the background behind dense grass.
August 8, 2025 at 5:23 PM
ericrlarson.bsky.social
This was another barrier where non-native crayfish passage was obvious before we started sampling. Here a small gate in one of the water control structures was clogged with carcasses from the upstream pool. I think this barrier is open to flow at times of the year when crayfish are moving around.
A cat door-sized panel in a water control structure or dam that is partially open but clogged with debris, letting out a small flow of water. A close-up of a small panel or gate in a water control structure that is clogged with both aquatic plant debris and noticeable crayfish carcasses, including visible walking legs and abdomens
August 7, 2025 at 6:11 PM
ericrlarson.bsky.social
This irrigation diversion looked promising as an invasive crayfish barrier. The diversion gates didn't appear to be climbable. Water is diverted into a buried pipe with screens to prevent fish entrainment. Concrete retaining walls extend into the riparian zone. Can crayfish get over or around this?
An irrigation diversion in an arid landscape backing up water behind it, with a shallow, rocky stream below. The diversion consists of a series of concrete retaining walls and metal water controls that can be raised or lowered.
August 6, 2025 at 2:08 PM
ericrlarson.bsky.social
A relief to add a new pilose crayfish site this week. This native species disappeared from the mainstem, low elevation Bear River in Wyoming between 1987 & 2007, replaced by the non-native virile crayfish (peerj.com/articles/5668/). Remnant populations are confined to higher elevation tributaries.
A pilose crayfish (Pacifastacus gambelii) held close to the camera with a five gallon bucket and clipboard out of focus in the background on a grassy river bank. The pilose crayfish is mottled olive brown and yellow, with distinctive strips of hair on the lateral, dorsal surface of its visible claw.
August 1, 2025 at 8:55 PM
ericrlarson.bsky.social
Freshwater invaders pose unique challenges to species distribution (or ecological niche) models used in risk analysis. New in Freshwater Science (doi.org/10.1086/737200), I identify strategies to improve predictions of suitable habitat for emerging, data-poor freshwater invaders using these tools.
The manuscript title "Predicting potential distributions of freshwater invasive species in novel environments" above the author Eric R. Larson and an affiliation at the University of Illinois, with a conceptual figure illustrating the transfer of invasion risk information from a widely distributed to an emerging, prospective invasive species. The figure's caption from the paper reads "Researchers might borrow information from supraspecific modeling units, sometimes termed avatar species or surrogate species, to make precautionary habitat suitability estimates for species under evaluation as prospective invaders that lack nonnative occurrence records. The simple example here uses BioClim bounding boxes (Busby 1991) on only 2 predictor variables to quantify underestimation of abiotic tolerances for a widely distributed invader when using only native-range occurrences relative to a total model that incorporates nonnative occurrences (A). The magnitude of this underestimation can be transferred to a species with only native-range occurrence data under evaluation as a prospective invasive species (B). Transferring this information may need to account for asymmetrical shifts in abiotic tolerances or changes in the direction of relationships between multiple predictor variables (Larson et al. 2014) and might also use the supraspecific modeling unit to identify total range-informed thresholds of habitat suitability for transfer (Liu et al. 2005)."
July 31, 2025 at 7:44 PM
ericrlarson.bsky.social
One challenge in our work is that although considerable effort has been directed at fish passage and barriers in the study watershed, crayfish and fish differ in what barriers they can and can't pass (e.g., doi.org/10.1016/j.bi...).
Water plunging over a small concrete wall into a downstream, rocky river shot at a low angle to the stream, with a riparian forest of willows and aspen in background below a partly cloudy sky.
July 31, 2025 at 4:36 PM
ericrlarson.bsky.social
It didn't take much investigation here to conclude this wasn't a barrier to crayfish. We start from a variety of databases in our study watershed (e.g., doi.org/10.1002/rra....) to identify prospective barriers, but need to get in the stream to check out the structure and look for crayfish above it.
A researcher in chest waders holding a measuring tape and clipboard standing in a shallow, rocky river downstream of a concrete water control structure that is at grade with both the upstream and downstream bed of the river. The water control structure might be slippery or hard to walk across for a crayfish, but current velocity was too low to exceed the swimming ability of crayfish.
July 31, 2025 at 4:13 PM
ericrlarson.bsky.social
Here's another potential invasive crayfish barrier: a concrete structure extending across a river channel associated with a municipal water supply diversion. Can crayfish get over/around this, or not?
A view across a river channel centered on a small concrete dam or water control structure, which extends into the riparian zone and has a noticeable drop or plunge at its downstream end. The river is shallower and rocky below the dam and deeper above.
July 30, 2025 at 3:00 PM
ericrlarson.bsky.social
More hints that one of our study sites is a good place to catch crayfish
A latrine pile of crayfish fragments with a low gradient river in the background
July 29, 2025 at 7:33 PM