Marine Invertebrates of Bermuda

Bermuda Glow Worm (Odontosyllis enopla)

By Molly Anne Jones
James B. Wood (Ed)

Abstract  Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links 

Bermuda Glow Worm, Odontosyllis enopla


Odontosyllis enopla is a syllid polychaete found in benthic communities in the shallow waters of Bermuda. It is commonly believed that the benthic forms of O. enopla are tube dwellers. They are of particular interest to the inhabitants, visitors and researchers of Bermuda because they produce luminous mating displays; however, many aspects of their ecology have yet to be explored. Members of this species possess a tremendous ability to appear at the same time each night after the full moon of each month, and scientists agree that O. enopla uses lunar periodicity to time their emergence. Once they emerge, the males and females engage in an elaborate courtship after which the gametes are released. This type of broadcast spawning has proven to be quite successful. One reason for the high reproductive success of O. enopla may be that much of the morphology of this species is dedicated to reproduction. Examples include the fiber optic eye structures which aid the males in locating the luminescent females, the large body cavities capable of holding large numbers of gametes, and the glands in the epidermis which contain bioluminescent reactions. Additionally, this species has an epitokous life cycle in which the benthic forms undergo a metamorphosis in order to become pelagic forms capable of reproducing closer to the surface. This epitokous metamorphosis is reversible, and individuals often return to the benthos following spawning events. The product of reproduction in O. enopla is a lecithotrophic larvae that quickly transitions to a benthic juvenile form.




Individuals of the species Odontosyllis enopla are found in shallow benthic communities in the waters of Bermuda and preferentially settle on hard substrates such as rock, in sandy areas or in sea grass beds (Markert et al. 1961; Franke 1999). Specifically, scientists have observed O. enopla in the Flatts Inlet to Harrington Sound, in St. George’s Harbor and at the end of Ferry Reach, though they are found in varying abundance (Galloway and Welch 1911; Markert et al. 1961).

In laboratory work by Fischer and Fischer (1995), scientists observed adult and juvenile worms constructed half-cylinder webbed tubes. Although juveniles were never seen dwelling in tubes in nature throughout their study, Fischer and Fischer (1999) concluded that their comfortable behavior in and around the tubes proved to be ample evidence to suggest that they do live in tubes as juvenile worms as well. The same study revealed that tubes were built in aggregations with multiple worms of both sexes living in the same tubes.


Odontosyllis enopla, commonly known as the Bermuda Fireworm or Bermuda Glow Worm, is a polychaete annelid worm inhabiting the shallow sublittoral waters of Bermuda. This and similar species have captured the imagination of people for ages. In fact, a legend claims that the luminescent spawning ritual of a related species was seen by Christopher Columbus and his crew several hours before they first made landfall in America, and it is the bioluminescence of O. enopla that gives it its name (Fischer and Fischer 1995). Despite their popularity among Bermuda’s inhabitants, visitors and researchers, some of the first scientists to observe these worms said it best when they claimed, “Nothing is known of the habits and manner of life of this species of Odontosyllis except what is seen in this mating period…” (Galloway and Welch 1911). In fact, what is known outside the realm of reproduction is still peripherally related primarily because species within the Syllidae family are masters of reproductive success (Franke 1999). Even their morphology and physiology is dedicated to maximizing the potential reproductive output of these organisms.

Many species in the genus Odontosyllis including O. enopla are broadcast spawners and participate in sophisticated mating rituals that occur each month following the full moon (Fischer and Fischer 1995; Franke 1999). Numerous researchers have observed these events and have commented on the tremendous precision in the timing of the appearance of the worms. Depending on the study location, the greatest abundance of worms occurs either the second or third night after each full moon, and more worms are observed in the summer months as opposed to the cooler months; however, it is common that the events begin approximately 55-56 minutes after astronomical sunset and last between 10 and 30 minutes (Galloway and Welch 1911, Markert et al. 1961, Fischer and Fischer 1995, Franke 1999). Markert et al. (1961) suggest that the impetus for the beginning of the event is a fixed interval of darkness following sunset, and Franke (1999) believes nocturnal swarming is an adaptation to avoid predation.

The reproductive event is very complex. There is some controversy regarding the exact mechanism that allows for the luminescence of O. enopla, although it is widely accepted that one mechanism of bioluminescence occurs when luciferin is oxidized by luciferase, a reaction that produces light (Shimomura and Johnson 1967). This is believed to be the case for the Bermuda Fireworm; however, researchers are recently entertaining the possibility that bioluminescence in some species of Odontosyllis requires a photoprotein instead (Deheyn 2006). During the bioluminescent displays of O. enopla, the females release a luminescent slime and swim in slow circles about 2 cm below the surface of the water while continuously emitting light (Fischer and Fischer 1995). Galloway and Welch (1911) purported this slime to be the eggs of the female and the associated body fluids as well as fluid from within the phosphorescent glands located in the epidermis. The smaller males respond to this activity by emitting short pulses of light as they swim from deeper water toward the slow-swimming females, and often more than one male will participate in the nuptial dance of rotating mates as all of the participants release their respective gametes into the water (Galloway and Welch 1911). In their study of O. enopla, Galloway and Welch (1911) determined from random samples taken after the spawning event that 45-80 percent of the eggs were fertilized, confirming the efficiency of the worms reproductive strategy.

A couple factors function synergistically to account for the reproductive success in O. enopla. The first is the behavioral dimorphism between the sexes and the second is the eye structure of the males (Galloway and Welch 1911; Markert et al. 1961; Wolken and Florida 1984; Fischer and Fischer 1995). In adult O. enopla, there are four eyes with two situated on either side of the median line on the dorsal surface of the head (Wolken and Florida 1984). Although females are significantly larger than the males, the eyes of the males are much larger, which helps explain the precision they demonstrate in locating the females during swarming (Markert et al 1961). Also, according to electroretinogram tests run by Wilkens and Wolken (1981), the visual peak of Odontosyllis eyes correspond with the wavelengths emitted by the luciferin-luciferase system. This is further evidence that the male fireworms are particularly suited for locating luminescent females.

Reproduction significantly dictates the life history of O. enopla. Many species in the Syllidae family are epitokous (Fischer and Fischer 1995; Franke 1999). Epitoky is a life stage in which the species undergoes a metamorphosis behaviorally, morphologically and physiologically (Franke 1999). In O. enopla, the entire organism is transformed from a benthic or atokous form to a pelagic, reproducing form (Franke 1999). Franke (1999) describes this phase as involving the following transformations: The eyes become considerably larger, swimming setae develop and the nephridia are modified to allow for the storage of gametes. He also explains that for many species like O. enopla, the process of epigamy is reversible, as individuals often survive the swarming ritual, return to a life in the benthos and even breed again.

Following fertilization, swimming trochophore larvae emerge after 24-48 hour, after which there is a short period of pelagic larval development (Franke 1999). O. enopla may limit the length of the lecithotrophic larvae development in order to confine the offspring to areas of appropriate habitat (Franke 1999). The larvae are able to leave the bottom but may also attach to the substrate by means of thin threads secreted from their posterior end (Nybakken 1993).

There is little information regarding the diet of O. enopla available at this time, but the method of feeding is well-documented. O. enopla is a carnivorous worm that feeds by use of its head appendages. After encountering a potential source of food, O. enopla uses its neurosensory cirri to probe the prey while simultaneously moving its foregut forward and everting the opening to its pharynx (Fischer and Fischer 1995). The last steps in feeding are to quickly bite the prey by everting its teeth and pharynx and swallowing the prey whole.

Recent Research

Studies regarding Odontosyllis enopla reproduction as it compares with other polychaete annelids have been conducted (Franke 1999). Franke (1999) surveyed the reproductive behaviors of polychaetes in the family Syllidae, drew comparisons, and analyzed the physiological and environmental restraints on sexual reproduction; however, the difficulty of conducting studies in a laboratory setting makes future investigations necessary. The ultimate goal of such studies is to establish a sound phylogeny for annelids in the family Syllidae (Franke 1999).

In addition to studies focusing on reproduction, there are numerous studies aimed at characterizing bioluminescence in O. enopla (Deheyn 2006). Through chemical analyses in all life cycles of species of Odontosyllis, Deheyn (2006) demonstrated that bioluminescence is a multi-purpose tool.

Commercial Importance

The illuminated mating display of Odontosyllis enopla is a spectacular show for tourists and local Bermudians alike. Several businesses and even the Bermuda Underwater Exploration Institute take advantage of the natural phenomenon by offering one night “Glow Worm Cruises” each month during the summer. Cruise tickets can cost up to 40 U.S. dollars per person.

Bermuda Laws

There are no specific Bermudian laws protecting Odontosyllis enopla, though there are numerous laws regarding the preservation of Bermuda’s waters. Beginning in the 1970s primarily with the Fisheries Act of 1972, the government of Bermuda established three seasonal and 29 permanent protected areas. In these marine-protected areas, or no-take zones, the removal of all marine life including O. enopla is prohibited (Wood and Jackson 2005).

Personal Interest

Prior to arriving in Bermuda for a semester of studies at the Bermuda Institute of Ocean Sciences, I read about the mating ritual of the Bermuda Glow Worm in my guidebook and became immediately intrigued. I marveled at the punctuality of such a seemingly “primitive” organism and wondered why I myself can never be on time.

My interest in Odontosyllis enopla was strengthened two nights after the full moon in February, 2007. The class headed out to view what we thought would be an orgy of fireworks and splendor; however, we were only able to see a few lonely males and no orgy at all. Although we were thwarted in our surveying effort, it was amazing to view bioluminescence in the few males, as such as display is rarely seen on land, or in all of nature for that matter.


Deheyn, D.D. 2006. Bioluminescence characteristics of the marine worm Odontosyllis phosphorea. Luminescence. Vol. 21.

Fischer, A. and U. Fischer. 1995. On the life-style and life-cycle of the luminescent polychaete Odontosyllis enopla (Annelida: Polychaeta). Invertebrate Biology. Vol. 114.

Franke, H. 1999. Reproduction of the Syllidae (Annelida: Polychaeta). Hydrobiologia. Vol. 402.

Galloway, T.W. and P.S. Welch. 1911. Studies on a phosphorescent bermudian annelid, Odontosyllis enopla verill. Transactions of the American Microscopical Society. Vol. 30.

Markert, R.E., B.J. Markert and N.J. Vertrees. 1961. Lunar periodicity in spawning and luminescence in Odontosyllis enopla. Ecology. Vol. 42.

Nybakken J.W. 1993. Marine biology: an ecological approach. 3rd edition. Harper Collins College Publishers, New York. 462 pp.

Shimomura, O. and F.H. Johnson. 1968. Light-emitting molecule in a new photoprotein type of luminescence system from the euphausid shrimp Meganyctiphanes norvegica. Proceedings of the National Academy of Sciences of the United States of America. Vol. 59.

Wilkins, L.A. and J.J. Wolken. 1981. Electroretinograms from Odontosyllis enopla (polychaete; syllidae): initial observations on the visual system of the bioluminescent fireworm of Bermuda. Marine Behavioral Physiology. Vol. 8.

Wolken, J.J. and R.G. Florida. 1984. The eye structure of the bioluminescent fireworm of Bermuda, Odontosyllis enopla. Biological Bulletin. Vol. 166.

Wood, J.B. and K.J. Jackson. 2005. Bermuda in: Caribbean marine biodiversity: the known and the unknown. Miloslavich, P. and E. Klein eds. DEStech Publications, Inc. 19-36.


Biological Institute of Ocean Sciences
Integrated Taxonomic Information System