The biological effects of heavy ions were studied in silkworm larvae following irradiation using the depth control plant seed irradiation equipment currently installed in TIARA, JAERI. Larvae were irradiated at a whole-body or a local level with 50-MeV4He2+, 220-MeV12C5+, or 350-MeV20Ne8+ ions, and the survival rates and morphogenesis after irradiation were investigated. For individuals exposed at the whole-body level, the sensitivity to heavy ion beams increased, as measured by changes in pupation and emergence rates. Similar results were observed for all three kinds of irradiation: (a) for the larvae at the same developmental stage, the bio-effects increased with irradiation dose; (b) the projectile range caused greater effects than did LET. The different beams or the different track sections of the same beams had different bio-effects on ovary tissues and dermal cells. Adjusting the projectile range with Mylar film showed that greater bio-effects were clearly observed the nearer the organic target was to the Bragg Peak. Thus, bio-effects of heavy ion-ray radiation on silkworms were considered to be different than those seen for smaller targets such as cells and plant seeds. Following whole-body irradiation, the effects caused by different beams on larvae were varied and depended on stronger projectile ranges than those of LET. For local irradiation, the bio-effects of irradiation on larvae greatly depended on the track site of the target: the closer the target was to the Bragg peak, the more effects were observed.