The present account of the distribution and ecology of tsetse-flies (Glossina) in Liberia is based primarily on observations made from December, 1943, to August, 1944, for the American Foundation for Tropical Medicine, Inc. I have included some information obtained on an earlier brief stay in the same territory, from July to November, 1926, as a member of the Harvard African Expedition under the leadership of Dr. (now Colonel) Richard P. Strong.
It seems essential to introduce the discussion of the Liberian tsetses with a concise description of environmental conditions. Of the twenty-one species of Glossina generally recognized at present, only four are efficient vectors of human trypanosomiasis, while the others are negligible, not being positively known to transmit the disease. The occurrence, abundance and habits of each species are closely correlated with the outside factors, or the environment, particularly as they concern the spread of the disease.