VIETNAMESE BAIT WORMS: GREAT BAIT OR INVASIVE INTRODUCTION?VIETNAMESE BAIT WORMS: GREAT BAIT OR INVASIVE INTRODUCTION?Doug Miller1, Pamela Davey Huggins2, Christine Muir1, Abigail Bradley1, Jill Brown1 and Ryan Dale1

1Graduate College of Marine Studies, University of Delaware, Lewes, DE, USA 2Fairmont State College, Fairmont, WV, USA

What are these worms?

Sold as “nuclear worms” or “nukes,” Vietnamese bait worms are polychaetes (segmented marine worms) which belong to the genus Namalycastis and the family Nereididae. They are related to the common clam worm of the east coast of the US, except they’re much bigger.

How big are they?

Large specimens can reach lengths of 300 cm (9 feet) in the wild. Cultured specimens at the College of Marine Studies are a more modest 100-200 cm (3-6 feet) in length.

Where are they from?

Most members of the genus Namalycastis inhabit low salinity areas in tropical and subtropical regions of the world. “Nuclear worms” are shipped to the U.S. from the Mekong Delta in Vietnam.

Why are they imported from Vietnam?

“Nuclear worms” were first introduced to the Mid Atlantic region in the mid 1990s for use as bait. Each worm can be cut into over 40 pieces, making them relatively cost effective. Also, unlike other worms, “nuclear worms” neither bleed when cut nor bite when annoyed.

Why are scientists studying Vietnamese bait worms?

They are a previously undescribed species of polychaete. If they were accidentally released into the environment, they might become an invasive species. Or not…we just don’t know right now.

“The biggest, baddest, pinkest polychaete of them all.”

During the summer of 2002, “nuclear worms” received a lot of media attention because their packing material contained potentially harmful bacteria. However, scientists still had very little information about the worms themselves. Therefore, we decided to study some of their basic natural history.

Salinity tolerance

“Nuclear worms” are remarkably tolerant of a wide range of salinities, from nearly fresh water to full-strength seawater. They are termed “euryhaline” and adapt to changing salinity by absorbing or releasing water from their body fluids.

Temperature limits

“Nuclear worms” like it hot. They thrive at 30-35 °C (88-96 °F) and 90-100% relative humidity—in a word, tropical conditions. Interestingly, however, nuclear worms can survive to near 12 °C (mid-low 50’s °F) if they are slowly acclimated to dropping temperatures.

Where they live and what they eat

Vietnamese bait worms do quite well in our lab under conditions which simulate local salt marshes. In culture, they inhabit shallow burrows in mud underneath decaying vegetation. They appear to be tolerant of hypoxic conditions, although like all marine invertebrates, they respire aerobically and are poisoned by high levels of H2S. Fecal pellet analyses suggest that nuclear worms are nonselective deposit feeders and will ingest anything they can fit into their mouths, including sediment, seaweed and cellulose fiber.

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Great bait or introduction of an invasive species?

Judging by their sales at local bait shops, “nukes” are a popular bait. Because they require tropical temperatures, it is generally thought unlikely that this species could over winter in the Mid Atlantic region and become established, and there is no indication that they would become a pest species. To provide scientific support for these assertions, we are continuing laboratory experiments to delimit which areas of the Southeast US coast are susceptible. Next summer, we plan additional experiments to study their survival when cut for bait, their ability to regenerate, their live prey diet and any potential impact on other local fauna.

Research supported by the Aquatic Nuisance Species Research and Outreach program of the National Sea Grant Office.