Eric R. Larson
@ericrlarson.bsky.social
Associate professor in freshwater ecology, University of Illinois at Urbana-Champaign. Crayfish, invasive species, environmental DNA, and more. https://publish.illinois.edu/erlarson/
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.
November 10, 2025 at 5:04 PM
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.
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.
September 24, 2025 at 9:29 PM
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.
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.
September 6, 2025 at 3:00 PM
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.
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).
August 20, 2025 at 9:24 PM
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).
So ... any crayfish in this small and declining habitat?
August 19, 2025 at 3:48 PM
So ... any crayfish in this small and declining habitat?
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.
August 19, 2025 at 3:46 PM
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.
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.
August 8, 2025 at 9:38 PM
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.
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?
August 8, 2025 at 5:32 PM
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?
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.
August 8, 2025 at 5:23 PM
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.
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.
August 7, 2025 at 6:11 PM
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.
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?
August 6, 2025 at 2:08 PM
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?
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.
August 1, 2025 at 8:55 PM
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.
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.
July 31, 2025 at 7:44 PM
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.
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...).
July 31, 2025 at 4:36 PM
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...).
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.
July 31, 2025 at 4:13 PM
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.
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?
July 30, 2025 at 3:00 PM
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?
More hints that one of our study sites is a good place to catch crayfish
July 29, 2025 at 7:33 PM
More hints that one of our study sites is a good place to catch crayfish
There's excellent barrier work in Europe, and in the US emphasis on protecting ESA-listed Shasta Crayfish from invaders (doi.org/10.1093/jcbi...). We're working from existing literature and reports to assess barriers by flow velocity, vertical drop, and risk of climbing or overland passage.
July 29, 2025 at 3:37 PM
There's excellent barrier work in Europe, and in the US emphasis on protecting ESA-listed Shasta Crayfish from invaders (doi.org/10.1093/jcbi...). We're working from existing literature and reports to assess barriers by flow velocity, vertical drop, and risk of climbing or overland passage.
Here's another potential invasive crayfish barrier: a road crossing above a concrete slab with a drop to a downstream pool. In this case we couldn't assess if the barrier was passable because we found no crayfish up or downstream of the road, likely because the stream is intermittent.
July 24, 2025 at 3:33 PM
Here's another potential invasive crayfish barrier: a road crossing above a concrete slab with a drop to a downstream pool. In this case we couldn't assess if the barrier was passable because we found no crayfish up or downstream of the road, likely because the stream is intermittent.
For sick or dead crayfish, we're especially looking for porcelain disease, which causes milky or opaque muscle tissue under the abdomen, or the crayfish plague, which might look like lesions or melanized spots on the exoskeleton
July 23, 2025 at 6:31 PM
For sick or dead crayfish, we're especially looking for porcelain disease, which causes milky or opaque muscle tissue under the abdomen, or the crayfish plague, which might look like lesions or melanized spots on the exoskeleton
Yeah, crayfish store calcium in stomach stones or gastroliths to help remineralize their exoskeleton after a molt. The stomach stones look like little white pills or pebbles and are durable enough to be routinely found on the shores of rivers and lakes.
July 23, 2025 at 2:08 PM
Yeah, crayfish store calcium in stomach stones or gastroliths to help remineralize their exoskeleton after a molt. The stomach stones look like little white pills or pebbles and are durable enough to be routinely found on the shores of rivers and lakes.
We found many crayfish remains on the shore at this site, where I think they were driven to an exposed point by the prevailing wind. Disease transmission is a big risk from invasive to native crayfish, so we're always looking for evidence of disease or mass mortality events.
July 23, 2025 at 1:51 PM
We found many crayfish remains on the shore at this site, where I think they were driven to an exposed point by the prevailing wind. Disease transmission is a big risk from invasive to native crayfish, so we're always looking for evidence of disease or mass mortality events.
You can definitely find crayfish remains associated with predators. Here we have some crayfish fragments, including gastroliths or stomach stones, outside a den in a river bank. But at high density populations there are tons of molts, and those claws or other exoskeleton pieces can wash up on shore
July 23, 2025 at 1:34 PM
You can definitely find crayfish remains associated with predators. Here we have some crayfish fragments, including gastroliths or stomach stones, outside a den in a river bank. But at high density populations there are tons of molts, and those claws or other exoskeleton pieces can wash up on shore
Sometimes we know a crayfish is at a site before we even begin sampling. In this case, the hairy claws of the pilose crayfish had washed up on the shore of a reservoir from molts or mortalities.
July 23, 2025 at 1:23 PM
Sometimes we know a crayfish is at a site before we even begin sampling. In this case, the hairy claws of the pilose crayfish had washed up on the shore of a reservoir from molts or mortalities.