Rusty crayfish (Faxonius rusticus)

Common Names: rusty crawfish, rusty crawdad

Description:

Rusty crayfish (Faxonius rusticus) is an invasive freshwater crayfish native to the Ohio River basin of the central United States [1][6]. It has spread far beyond that range, largely because anglers use it as live bait and dump leftover bait into new waters [1]. MISIN tracks it because it strips aquatic plants, eats fish eggs and young, and pushes out native crayfish wherever it takes hold [2][4].

Identification:

Rusty crayfish is a sturdy, lobster-shaped crustacean that grows up to about four inches (10 cm) long, not counting the claws [1]. Its body is grayish to reddish brown, and the clearest field mark is a pair of dark, rusty-red spots ? one on each side of the shell, just in front of the tail ? that look as if the animal was picked up with paint-stained fingers [1][3]. The claws are large and grayish-green with black bands near the tips, and a clear oval gap stays open between them when the claws are closed [1][3]. The rusty spots can be faint or missing on young animals, so check the claws too [3].

Look for rusty crayfish from late spring through early fall, when warm water makes them most active. They hide under rocks, logs, and debris by day and move into the shallows to feed at night, so dusk and after-dark are the best times to spot or trap one [1][2].

At-a-glance cues:

1. A dark, rusty-red spot on each side of the shell, one per side [1][3]
2. Large grayish-green claws with black bands near the tips [1][3]
3. An oval gap stays open when the claws are closed [1][3]
4. Reaches about four inches (10 cm) long, not counting the claws [1]

Habitat:

Rusty crayfish lives in lakes, ponds, rivers, and streams [1][2]. It prefers areas with rocks, logs, or other debris that give it cover, and it does well over many bottom types, from gravel and rock to silt and clay [2]. It tolerates a wide range of water conditions, which helps it settle into new lakes quickly [1].

The species is native to the Ohio River basin ? parts of Ohio, Indiana, Kentucky, and Tennessee [1]. Through bait-bucket releases and other human movement, it has spread across roughly twenty states, including the Great Lakes region and many waters across the Midwest and Northeast [1].

Reproduction:

The main reason rusty crayfish reaches new lakes is people. Anglers buy it as live bait and then dump the leftover bait ? and any crayfish in it ? into the water they are fishing [1][2]. It also spreads when classroom or aquarium animals are released and when it hitchhikes on boats, traps, and gear moved between waters [2]. Because a single mated female can start a new population, even one released crayfish is a risk [3].

Adults mate in late summer, early fall, or early spring, and the female carries the fertilized eggs under her tail [1]. A female lays roughly 80 to 575 eggs, which hatch in three to six weeks depending on water temperature [1]. Young crayfish reach breeding age in about a year and adults live three to four years, so a new population can build fast [1]. The practical lesson for control: never move crayfish or live bait between waters, and never release them.

Impact and Damage:

For most people, the damage from rusty crayfish shows up in the lakes and streams they fish, swim, and live beside. It is a heavy feeder that mows down underwater plant beds ? the same beds that shelter young fish and the insects and other small animals fish eat [2][4]. It also eats fish eggs and young fish directly, which can lower the numbers of popular sport fish over time [2].

In one long-term study of a northern lake, the spread of rusty crayfish was followed by a drop of as much as 80% in the variety of underwater plants at some sites, along with a collapse of native snail populations [4]. The same work documented native crayfish being pushed out as rusty crayfish became far more abundant [4]. Rusty crayfish can also breed with some native crayfish, replacing native populations with hybrids and erasing the local species.

These changes ripple outward: thinner plant beds mean less cover and food for fish and waterfowl, murkier water, and a simpler, less stable lake community [2][4].

Similar species:

Several native crayfish are mistaken for rusty crayfish, and one other invasive looks similar. The rusty-red spots on the sides of the shell plus the black-banded claw tips are the best combination to check.

Virile (northern) crayfish (Faxonius virilis) is a common native often confused with rusty crayfish. It is large and reddish-brown to green but lacks the bold rusty side spots, and its greenish claws are studded with pale knobs and tipped in orange rather than ringed with black [2][5].

Calico (papershell) crayfish (Faxonius immunis) is a native look-alike with grayish, purplish, or pink claws and a pale stripe running down the middle of the back, and it has no rusty side spots [5].

Northern clearwater crayfish (Faxonius propinquus) is a native species similar in size and shape, but it lacks the paired rusty side spots and the dark bands on the claw tips [2].

Red swamp crayfish (Procambarus clarkii) is another invasive crayfish, but it is usually dark red with raised bright-red bumps on the claws and body, very different from the smoother, black-banded claws of rusty crayfish [2].

Monitoring and rapid response:

Signs to watch for:

1. Crayfish with a rusty-red spot on each side of the shell and black-banded claw tips, especially in the shallows at dusk or after dark from late spring through early fall [1][3]
2. A sudden drop in underwater plants, snails, or native crayfish in a lake or stream you know well [4]

What you can do:

1. Never release live bait, aquarium crayfish, or classroom animals into any water ? dump unused bait in the trash, well away from the shoreline [2]
2. Clean, drain, and dry boats, traps, waders, and gear before moving between waters so you do not carry crayfish or young to a new lake [2]
3. On a small private pond, repeated trapping through the summer can knock back numbers, though it rarely removes an established population on its own [2]
4. Natural area crews and lake associations can run coordinated, multi-year trapping and protect or restore fish that prey on crayfish; focusing on small, newly found populations first gives the best chance of stopping spread [2][4]

When to call a professional:

1. Large or well-established infestations, or any whole-lake or stream-wide control effort, need a fisheries biologist or your state natural-resources agency ? there is no simple do-it-yourself fix for crayfish already spread through open water [2]
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Faxonius rusticus (Rusty Crayfish) Species Profile. nas.er.usgs.gov
2. Minnesota Department of Natural Resources. Rusty crayfish (Faxonius rusticus). dnr.state.mn.us
3. University of Minnesota Extension. Rusty crayfish. extension.umn.edu
4. Wilson KA, Magnuson JJ, Lodge DM, Hill AM, Kratz TK, Perry WL, Willis TV (2004). "A long-term rusty crayfish (Orconectes rusticus) invasion: dispersal patterns and community change in a north temperate lake." Canadian Journal of Fisheries and Aquatic Sciences 61(11):2255?2266. semanticscholar.org
5. Missouri Department of Conservation. Identifying Crayfish: A Guide for Bait Vendors and Aquaculturists and field-guide entries for virile and calico crayfish. mdc.mo.gov
6. Integrated Taxonomic Information System (ITIS). Faxonius rusticus (Girard, 1852), TSN 1133773. itis.gov

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