Do Snow Crab Legs Have Parasites? What You Need to Know

December 8, 2025 •

4 min read

Visible black or brown spots on snow crab shells often alarm consumers, but these blemishes are typically the harmless cocoons of marine leeches, not a threat to human health. When properly cooked and prepared, snow crab legs are a delicious and safe meal.

Quick Summary

The presence of external organisms like marine leech eggs and barnacles on crab legs is common and poses no threat to humans, especially when cooked. Internal parasites are also neutralized by proper cooking methods.

Key Points

Visible Blemishes are Harmless: The black spots on snow crab legs are typically marine leech egg sacs, which are not harmful to humans.
Cooking Kills Parasites: The commercial cooking and freezing process effectively eliminates any external or internal organisms, ensuring the crab meat is safe to eat.
External is not Internal: Organisms like leech cocoons and barnacles are external and do not affect the quality or safety of the crab meat.
Indicators of Age: The presence of these external growths can sometimes indicate a crab that is older or has not molted recently, which can mean more meat inside.
Proper Cleaning is Key: While harmless, you can easily scrub off or rinse away any unwanted spots or barnacles from the shell before reheating.

Understanding the Blemishes: What's on Your Crab Legs?

It is a common sight for diners to find small, dark spots or rough patches on the shells of their snow crab legs. For many, this can be an immediate cause for concern, with worries about parasites or spoiled seafood. The truth is, these are typically not a sign of danger to the consumer, but rather a normal part of the crab's life cycle and marine habitat. The most frequent culprits behind these external markings are marine leech cocoons and barnacles, both of which are benign when it comes to human consumption.

Marine Leech Eggs and Barnacles

The most prevalent external 'parasites' found on snow crab legs are the egg sacs, or cocoons, of a type of marine leech, such as Notostomum cyclostoma. These cocoons are small, black, and often have a seed-like appearance. The leeches lay their eggs on the crab's shell, using the crab as a mobile transport host. This relationship is an example of commensalism, where the leech benefits from the protection and transport provided by the crab, while the crab itself remains unharmed. The eggs do not penetrate the shell and, importantly, are not harmful to humans if ingested, especially since the shells are not eaten.

Another common sight is the presence of barnacles, which are small crustaceans that attach themselves to hard surfaces. Like leeches, barnacles attach to the crab's shell but do not affect the meat inside. They are filter-feeders that simply use the crab's shell as a safe place to anchor and feed. The presence of barnacles or heavy deposits of leech eggs can sometimes indicate a crab that has not molted recently, which some consider a sign of a fuller, meatier crab.

Proper Cooking and Preparation Ensure Safety

Regardless of what might be on the shell, proper cooking is the most crucial step for ensuring food safety. Commercial snow crab legs are typically pre-cooked, frozen, and then reheated by the consumer. The initial cooking process, as well as the reheating, effectively kills any organisms present on or in the crab. When reheating at home, you should always follow safe cooking guidelines to bring the crab legs to a safe internal temperature.

Here are some best practices for preparing snow crab legs:

Rinsing: Before cooking, rinse the legs under cold running water to remove any loose debris, including external eggs or barnacles.
Scrubbing: If you find the appearance of the black spots unappealing, you can use a stiff brush or a butter knife to gently scrape them off the shell.
Thorough Cooking: Ensure the crab is heated through. For already-cooked crab legs, steaming or boiling for a few minutes until fragrant is sufficient. For raw crab, follow the recommended cooking time and temperatures to ensure complete safety. The presence of these external organisms should not prevent you from enjoying the meat inside.

Distinguishing Crab Parasites: External vs. Internal

While external organisms like leeches and barnacles are harmless to humans, some internal parasites can impact the crab itself. The most notable example is Sacculina carcini, a species of parasitic barnacle that can castrate and feminize its crab host. However, this parasite is found in the crab's internal tissues, not the meat itself, and is neutralized by the cooking process. It's crucial to understand that these biological issues do not pose a direct threat to human health when the crab is cooked, but they do have significant impacts on the crab's ecosystem.

Comparison of Crab Shell Blemishes


Feature	Marine Leech Cocoons	Barnacles	Sacculina (Parasitic Barnacle)	Black Spots (General)
Appearance	Small, black, seed-like bumps	Hard, greyish, conical or tube-shaped crustacean shells	Root-like filaments inside, external sac under abdomen	Discoloration from trauma or immune response
Location	Primarily on the external shell surface	External shell surface	Internal tissue, with an external sac	Shell surface
Effect on Crab	Commensal: uses crab for transport; generally harmless	Epibiont: harmless attachment to shell surface	Castration, feminization of male crabs, prevents molting	A natural healing process for minor shell damage
Human Risk	None; not eaten, killed by cooking	None; not eaten, killed by cooking	None; internal parts killed by cooking	None; external mark
Indicator Of	Indicates crab has been in its shell for some time	Indicates crab has been in its shell for some time	Internal infection, not visible to consumer in market crab	Minor injury, not a safety concern

Conclusion

In conclusion, while the sight of black spots, barnacles, or other external growths on snow crab legs might be disconcerting, it is not a reason for concern regarding your personal health. These are natural occurrences in the marine environment and, in the case of leech eggs, are simply attached to the outside of the shell. As commercially sold snow crab legs are already pre-cooked and frozen, any potential parasites, both internal and external, have already been neutralized. The key to safe and enjoyable consumption lies in proper preparation and reheating, ensuring the crab meat is thoroughly warmed. So next time you see some spots, simply wash them away and enjoy your meal with confidence, knowing the delicious meat inside is safe.

Visit the Alaska Department of Fish and Game's resource for more information on crab leeches and crustaceans.

Frequently Asked Questions

No, the black spots on snow crab legs are typically marine leech cocoons and are not harmful to humans. Since the crab is already cooked and you do not eat the shells, they pose no threat.

The small black spots are most often the egg capsules of marine leeches. Other possibilities include barnacles or natural melanization resulting from shell damage.

Yes, both the initial freezing and cooking processes are effective at killing any parasites, leeches, or bacteria that may be present on or in the crab legs.

Marine leeches lay eggs on the crab's exterior and are generally harmless to the host. Sacculina carcini is a parasitic barnacle that lives inside the crab's tissues, castrating and feminizing it, but is still not a concern for human safety with proper cooking.

No, there is no need to throw away crab legs with black spots. They are safe to eat after proper preparation. If the appearance bothers you, you can simply scrub them off.

It is highly unlikely to get sick from consuming properly cooked and prepared snow crab, even if it has external or internal parasites. The cooking process neutralizes any potential health risks.

For commercially sold crab legs, which are pre-cooked and frozen, it is difficult to determine the exact health of the live animal. However, the presence of barnacles or leech eggs is not an indicator of an unhealthy or unsafe product for human consumption.