Short course on Marmorkrebs

The Invasive Species Center is offering a short course on Marmorkrebs.

The course description:

This short course will provide an overview on crayfishes, with a particular focus on marbled crayfish biology, spread, and impacts.

Lesson 1: Introduction to Aquatic Invasive Species

Lesson 2: Introduction to Crayfishes

Lesson 3: Marbled Crayfish Biology

Lesson 4: Marbled Crayfish Impacts

Lesson 5: Preventing the Spread of Invasive Crayfishes

This course takes about 2 hours. Score an 80% on the final exam, and score a certificate of completion! 

The Center’s Instagram page has a discount code that lets you take the course for free until the end of May! If you happen to be reading this in June 2025 or later, sorry that it is no longer free, but should still be affordable.

External links

Invasive Species Training

Invasive Species Center on Instagram (contains discount code) 

Sheppard and Ricciardi 2025

Sheppard NLM, Ricciardi A. 2025. Influence of warming on the functional responses of invasive omnivores, Procambarus crayfishes. Canadian Journal of Fisheries and Aquatic Sciences 82: 1-8. https://doi.org/10.1139/cjfas-2024-0334

Abstract

The red swamp crayfish (Procambarus clarkii) and the marbled crayfish (Procambarus virginalis) are congeneric invasive species whose potential impacts in the Great Lakes basin have generated concern. In laboratory experiments, we tested the functional responses of these omnivores to two common food resources, insect larvae (Chironomus bloodworms) and aquatic macrophytes (Eurasian milfoil Myriophyllum spicatum), to gain predictive information on their per capita effects under present (18°C) and projected future (26°C) climate scenarios for the basin. The maximum feeding rate of P. virginalis was higher at 18°C than at 26°C when presented with bloodworms but did not differ between temperatures when presented with macrophytes. By contrast, the feeding rate of P. clarkii did not change with temperature for either food resource. Due to their larger mean size, P. clarkii exhibited higher rates of resource (bloodworm and macrophyte) consumption than P. virginalis at both temperatures. These results suggest that trophic impacts of P. virginalis will dampen with increased warming, whereas P. clarkii will sustain larger impacts irrespective of temperature within the range tested.

 

Keywords: None provided.

Talking Marmorkrebs to the streets

 

 

Pleased to hear that Marmorkrebs were part of a show promoting outdoor activities,

 

Brianna Naklicki from the Ontario Federation of Anglers and Hunters was handing out information booklets to visitors passing by. She works for the organization’s invasive species awareness program.

On a table in front of her are jars containing examples of species of concern in the province, including zebra mussels and marbled crayfish.

Her job at the show was to spread awareness about invasive species around lakes and forests to all who will listen.

 

Ontario is, so far, the only place in North America where Marmorkrebs have been found in the wild, and is the largest jurisdiction to ban Marmorkrebs.

External links

Outdoor show hooks nature lovers into shopping local

Update on Marmorkrebs in Warsaw, Poland

A couple of recent news articles are reporting on the presence of Marmorkrebs in Warsaw. This location was already in my map of Marmorkrebs introductions. A bioblitz located seven individuals in Morskie Oko Park back in 2019.

Fast forward six years to 2025, and the population is estimated at 100,000 crayfish.

 

The article notes that there are removal efforts, but they can’t drain the pond, so culling them requires catching them by hand or trap. And in typical local media style, they stress the expense.

 

I do appreciate the safety warning:

 

 The expert emphasized that rakes do not attack a person if they are not provoked to do so. 

I don’t know of any crayfish that voluntarily attacks people with anything more than a pinch.

External links

Wpuścił raka do stawu w Warszawie. "Doprowadził do niepowstrzymanej ekspansji" (He released a crayfish into a pond in Warsaw. “He led to unstoppable expansion”)

 

Warszawa zmaga się z inwazją raka marmurkowego. Ekspert ostrzega (Warsaw is struggling with marbled crayfish invasion, expert warns)

 

Photo by Adrian Grycuk - Own work, CC BY-SA 3.0 pl, https://commons.wikimedia.org/w/index.php?curid=101324805

Everyday sexism

Always nice to stumble across a video mentioning marbled crayfish. I’m kind of used to them showing some other random crayfish species, but this one has a new thing that made me pause.

This video is titled, “This guy copies himself 2,000 times!”

Since marbled crayfish are all female, a better title would be, “This gal copies herself 2,000 times.”

Eiler and colleagues 2025

Eiler A, Stensrud E, Osman O. 2025. Detection of marbled crayfish Procambarus fallax. protocols.io. https://dx.doi.org/10.17504/protocols.io.q26g78199lwz/v1

 

Abstract

Taqman QPCR assay for marbled crayfish Procambarus fallax.

 

Keywords:  None provided.

 

The Crayfish Almanac

Don’t know how I missed this last year, but Michigan State University released Great Lakes Almanac to Invasive Crayfish.

It has one of the best short identification guides for Marmorkrebs I’ve seen. Click to enlarge!

Marbled crayfish (or marmokrebs) originated in the aquarium trade and are often called the self-cloning crayfish. All marbled crayfish are female and the offspring are clones. This species is of high concern because a single individual can produce an entire population in a short time.

This species has a distinct marbling pattern, but other species may look similar. Male crayfish with this pattern are not marbled crayfish.

To determine if its a female, look for a round pocket-like feature located on the underside between the last pair of walking legs. This is the sperm pouch (called an ‘annulus ventralis’) .

External links

Great Lakes Almanac to Invasive Crayfish