In the 1990s, a mutant crayfish capable of conquering and degrading aquatic systems emerged as a result of secret German experiments gone awry. The marmorkreb, aka the marbled crayfish (Procambarus virginalis), is a new destructive species that first appeared in aquariums in Germany. However, it was more likely the result of too much inbreeding in captivity, rather than some mad scientist scheme, that led to their mutation. They are now here, and your help finding them is invaluable.
Maybe the only funny thing about these nasty aberrations of nature is the slight argument over how to describe them. Experts disagree on whether the new organisms are spotted, freckled, spotted, spotted, variegated or something else. The Germans insist that these crayfish are marmorated, a term unrelated to the word marmalade, which by the way is marmorated. Here in North America we have decided that they are marbled, although marmorkreb always sneaks into polite conversation.
These modified crayfish are medium to large in size, 10-15 cm (4-6 inches). Typically, they are olive to dark brown, but rarely appear reddish, blue, or beige just to throw us off. In addition, their pincers are narrow, with pincers thinner than those of native crayfish.
Either to compensate for their “little finger syndrome” or for no particular reason, marmorkrebs reproduce so quickly that they make rabbits look like celibate monks. The secret to spotted crayfish’s fertility is that a female lays viable eggs – around 700 on the fly – without having to search for a mate. All of his descendants are females, who soon mature and begin to clone themselves. This talent, known as parthenogenesis, is sometimes seen in insect species, but rarely in larger organisms. This saves them energy that they would otherwise waste scrolling through Tinder and Bumble, or however crayfish normally find mates. Being parthenogenic also means that a single individual can generate their own kingdom.
They are generalists who thrive in a wide range of habitats, from lakes and rivers to swamps and mud puddles. Running water does not seem to be a problem for them. They are cold hardy but also love heat. Not surprisingly, marmorkrebs eat a multitude of aquatic life, including algae, plants, amphibians, and snails. They burrow into the banks, which increases turbidity, releases nutrients from the sediments into the water and accelerates erosion.
A quick web search reveals alarming headlines of The New York Times, Atlantic, and other major news outlets claiming spotted crayfish are invading Europe. It’s not to the point that citizens are being driven from their homes by marauding arthropods, but marmorkrebs are becoming a real scourge in parts of Germany, the Netherlands and Italy. The island nation of Madagascar is particularly affected, in part because crayfish are considered a food source and sometimes deliberately propagated.
Unfortunately, marbled crayfish are sold on the web and even in some pet stores in the United States. While marmorkrebs are known to be prevalent here in the pet trade, at this time there are no reports of wild populations in New York State. This is where public awareness and citizen science come in. Invaders are dispersed when uninformed aquarium owners release excess crayfish from their tanks into surface waters, and when fishermen use them as bait. Populations are exploding rapidly, to the detriment of native aquatic species. It’s easier to engage the public when they learn that the spotted crayfish will spoil swimming, fishing and duck hunting in their favorite waterway.
A Michigan Department of Natural Resources fact sheet stresses the importance of early detection and public education: “Preventing the release of this species from the pet trade is a high management priority. In addition, early detection and public reporting will be essential to detect marbled crayfish prior to establishment. The Michigan MNR resource also states that “… owners of marbled crayfish should humanely dispose of specimens in their possession and thoroughly clean the tanks to ensure that no eggs or young remain. . “He notes that rinsing doesn’t necessarily kill crayfish and can potentially get them into a water system, and recommends freezing crayfish for at least 48 hours or soaking them in ethanol as a method of killing. cruelty-free.
Report possible sightings of marbled crayfish or other invasive species in the wild to the New York iMaps Invasives site at https://www.nyimapinvasives.org/ or to the St. Lawrence East Lake Ontario Partnership for the regional management of invasive species (SLELO-PRISME) in [email protected] or 315 387 3600 x7725
Paul Hetzler is a former natural resource educator with Cornell Cooperative Extension.