Her interest in zoology started when she was still a young girl and used to watch small animals in her father's microscope.

Together, they started a strong collaboration in zoology, including the study of several invertebrate groups, such as protozoans, ctenophores, flatworms, nemertines, annelids, tardigrades, onychophorans, bryozoans, gastropods, and pycnogonids.

She was not listed as an author in their first works together in order to justify Marcus' full-time position as a professor and because she never accepted a remunerated job.

[clarification needed] As a result, they dedicated their time to the study of freshwater and land invertebrates, especially turbellarians.

[1] After her husband's death in 1968, Du Bois-Reymond Marcus continued their studies, publishing about 30 papers, mostly on opisthobranch molluscs.