On a still morning in Berlin’s Britzer Garten, a fisherman wades waist-deep through the main lake. He is out to check his traps for crayfish. The fisherman, licensed to catch invasive red swamp crayfish (Procambarus clarkii), will pass his catches on for sale as delicacies. Berlin-born start-up Holycrab! transforms invasive species into gourmet products, such as regionally caught crayfish-infused beers and cooking stocks [1]. The invasive red swamp crayfish is just one of several invasive crayfish species in Europe, such as the signal crayfish (Pacifastacus leniusculus) and the spinycheek crayfish (Faxonius limosus). Throughout Europe, crayfish species are wreaking havoc on ecosystems, displacing native crayfish populations and spreading crayfish plague. Species native to Europe, such as the noble crayfish (Astacus astacus) and white-clawed crayfish (Austropotamobius pallipes), have been reduced in number by as much as 80% in some places [2].

“Holycrab!, a Berlin start-up, are the brains behind regionally caught crayfish-infused beers and cooking stocks.”

Another famous invasive species is the signal crayfish, known for the distinctive turquoise and white patches on its claws. Signal crayfish have long antennae, two front legs with large pincer claws, and eight additional legs for feeding and walking [3]. They are also characterized by a smooth ridge along the middle of the rostrum and can reach 16-18 cm long [4]. Like many invasive species in Europe, signal crayfish survive in a broad temperature and salinity range [5]. This means that they live in a variety of habitats, from headwater springs and streams to large rivers, lakes and wetlands, including in urban environments [3]. What’s more, they are highly mobile and can travel distances of up to 1 km overland to move between water bodies [6]. Signal crayfish take shelter under rocks and boulders, within tree roots or in burrows and cavities in banks [7].

Figure 1: Signal crayfish spreads to Europe. Drawing by author, Jun 2025.

Crayfish plague (Aphanomyces astaci) is caused by a fungi-like organism from North America. It is listed in the top 100 of the “World’s Worst” invaders by the International Union for the Conservation of Nature (IUCN) [5]. North American crayfish live in a balanced host-parasite relationship, meaning they are immune to its effects and are highly resistant to infection [5]. However, the crayfish plague can be fatal to many native crayfish species [4]. Since the 19th century, the plague has drastically spread across Europe, reducing native crayfish populations. In 1960, the signal crayfish was introduced in Europe in an plight to control the crayfish plague as it appeared to be immune to it. It was not yet understood, however, that the signal crayfish was a carrier of the disease and served to exacerbate the problem.

Signal crayfish are opportunistic polytrophic feeders (they feed on many kinds of food—plants, fish, and even other crayfish) [5]. They are bigger, grow and mature faster, and are more aggressive than native crayfish [8]. By burrowing into the banks of rivers, signal crayfish cause erosion, bank collapse and sediment pollution [9]. The burrows can be up to 2m deep, with interconnecting tunnels that weaken the bank. Their burrows can also displace threatened riverside species such as the water vole (Arvicola amphibius) [7]. The signal crayfish can have considerable impacts on other populations of macro-invertebrates, benthic fish, and aquatic plants. The species has even been introduced in fish farms to clear weeds from ponds [5]. By predating on fish eggs or taking the refuges of salmonid fish, signal crayfish can reduce the value of commercial fisheries [7].

Figure 2: Female signal crayfish (Pacifastacus leniusculus). Photo by Lisa Hupp/USFWS on Flickr. July 2017.