Calico Crayfish, Faxonius immunis


Mud crayfish, papershell crayfish


Faxonius, named for Walter Faxon (1848-1920), American ornithologist and carcinologist. Former genus, Orconectes, is from Orcus, god of the underworld in Roman mythology + nectes: swimming (Greek); immunis, unclear. Calico: mottled.

Ecology, Habitat, & Behavior

You won’t have luck finding these crayfish while flipping over rocks as they prefer the muddy bottoms of wide, slow flowing rivers or lakes with no flow (they can also live in ponds that dry up during the summer or on margins of pond that may be exposed to the air). These sites are characterized by high turbidity and low oxygen levels. Their preference for these habitats may be more a result of being pushed out by the more aggressive virile crayfish. In rocky, faster flowing streams, virile crayfish out compete the calico crayfish for refugia sites in rocks, and so calicos are relegated to the open, sandy bottom areas of these rivers.

Calico crayfish will burrow to in the summer to avoid drought and heat as well as in the winter (source). And they’ll burrow deep, excavating burrows 15 inches to 4 feet deep. Burrows are often capped with mud (to prevent drying out) and end with an enlarged cavity (source). In habitats that don’t drain and/or freeze, calico crayfish will content themselves with just bury themselves in the mud. While they can mature in about four months, time spent in burrows to avoid drought comes at a cost, extending maturation into the following year.

When calico crayfish are out, mostly at night, they spend most of their time scraping algae from rocks and eating aquatic vegetation. They will also opportunistically feed on invertebrates (e.g. midge larvae, isopods, etc.), and it’s possible that they feed on seedlings and roots when confined to their burrows. They have been studied for possible application in controlling aquatic vegetation, but they are not nearly aggressive enough to make this a viable option (source).

  • Avg carapace length: <2 inches
  • Life expectancy: 2 years
  • Age at maturity: 2nd summer
  • Habitat: Muddy bottoms of slow to stagnant water
  • # of eggs: 30-300
  • Diet: Algae
  • Native or non-native: Native
  • Activity pattern:

    Nocturnal (generally)

  • Uses: Fish bait, pet
Life History Event Date/Season
Mating Peaks in late summer, but can be anytime between June and October
Fertilization Delayed until spring
Males in F1
Males in F2
Laying Eggs Spring, as female emerges from burrow
Hatch in several weeks
Young detach from female After 2-3 molts, usually 7-19 days

Key features for ID + similar species

  1. Prominent notch at base of the dactyl
  2. Light band running down carapace and abdomen
  3. First pleopod on males sharply bent at 90 degree angle

Broad at base, sides convex tapering to an acumen. Margins lacking side projections. Deeply dished in middle.


Juveniles tend to have a greater contrast in coloration, but adults tend towards a less striking grayish green. Regardless of age, coloration is mottled, particularly on chelae (which can be pinkish/purplish), with a light band running down carapace and abdomen.


Slender, very mottled. Inner margin covered in light colored tubercles. Dactyl notched and toothed halfway up. Orange tipped. Male chelae have a purplish tint.


Narrow, with 2 rows of punctation (pits) in the middle.

General Research on Crayfish

  • NOBANIS: Invasive Alien Species Fact Sheet : source
  • Crayfish of the White River Watershed: source
  • Crayfish curriculum for educators: source
  • The Crayfishes of New England: source
  • Species of Ontario Crayfish: source
  • Lecture on Crayfish: video
  • Some aspects of the life histories of three closely related crayfish species, Orconectes obscurusO. sanborni, and O. propinquussource
  • Dictionary of crayfish names: source
  • Biological synopsis of the rusty crayfish: source
  • Observations on the life cycle of Procambarus acutus acutus in South Carolina culture ponds: source
  • Natural History of the two Crayfish of Northwestern Iowa, Orconectes virilis and Orconectes immunis: source