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Visitor Advisory

Visitor Advisory – Why are there so many flies on Alcatraz Island and on Alcatraz Cruises vessels?

During this time of year (September - November), one of the 17 identified species of flies on Alcatraz Island is found in large numbers around the dock area and on Alcatraz Cruises boats. These flies are commonly referred to as Cormorant flies, and they do not bite or pose a health risk to Island visitors. The presence of these flies is an indicator of a healthy population of cormorants on the Island. In the last few years, the cormorant population on the Island was decimated by several natural events. This year, the population is rebounding, so the fly population has temporarily increased. These flies are a very important part of the Island ecosystem and are not caused by any adverse conditions on Alcatraz Island or on Alcatraz Cruises vessels. We apologize for the annoyance these flies may cause and hope you will enjoy your visit to Alcatraz Island.

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