The undisputed position of English as the "international language of science" has resulted in a push for its use in college science classrooms in non-English-dominant contexts worldwide. This study uses classroom observation and interviews to examine the use of Spanish and English in college science classrooms at a land-grant university in Puerto Rico. Using an ecology of languages framework, and particularly drawing on Hornberger's Continua of Biliteracy for the study of learning in bilingual contexts, analysis of 15 class observations and interviews showed that professors used multiple classroom translanguaging practices to teach science. At the same time, they held strongly to the ideology of English as "the language of science" and believed it was important for all science students to use English. Thus, professors' practices and their ideologies rested on opposing ends of the context continua of biliteracy.