Some nests, investigation disclosed, were built of radioactive mud. It seemed obvious that the wasps were obtaining mud from radioactive waste pits or from the White Oak Lake bed, which is the site of a former 40-acre lake used for 12 years as a detention pool for radioactive wastes.[18] The mud daubers were carrying mud as far as 650 feet from the contaminated sources. Almost 90% of 112 nests built by the yellow-legged mud-dauber species were radioactive, and the mud was delivering to the wasp eggs each hour a dose of penetrating radiation equal to that received by a man from all natural sources over a period of many years. The development presented no human health problems, but further observation revealed a fascinating circumstance. At the same time, another variety of wasp, the pipe-organ mud dauber, was building nests only of _non_radioactive mud. Of 150 pipe-organ wasp nests examined, none was radioactive. The nests were found in similar locations, and it was apparent that the same sources of nest materials were available to both species. WASP NEST RESEARCH _Mud-dauber wasps, building nests of radioactive mud in a waste disposal area near an Oak Ridge, Tennessee, atomic plant, are the object of intensive environmental radiation study. A shows radioactivity reading from a nest. B is an enlarged view of the nest with two tiny dosimeters in place to measure radiation. In C an ecologist inspects new nests built in a laboratory flight cage from radioactive mud provided in pans at the bottom. In D wasps are anesthetized, marked with tiny plastic disks for future identification, and released._ The question, then, was why wasps of one species were using radioactive mud while the other species seemingly discriminated against contaminated mud. The muds appeared to be entirely alike. X-ray-diffraction studies showed no material differences, nor were there detectable differences in “feel”, smell, or plasticity. Radioactive isotopes in the mud included cesium-137, cobalt-60, ruthenium-106, and zinc-65. Oak Ridge scientists began to try to find out whether the pipe-organ wasps actually were discriminating against muds containing all or some of these radioisotopes or against the ionizing radiation from them. If so, how could the wasps detect it? These investigations were continuing in 1965. There is no answer yet. Survival of an Animal Population The case of Bikini already has been discussed as an example of a predominantly aquatic environment apparently recovering from association with nuclear experiment. Eniwetok offers an instance of the toughness of an animal population exposed both to direct and long-range radiological impact.