解析库 > 2021年考满分GPO新题模考
Monarch butterflies lay their eggs hundreds of miles away from their places of origin. Each caterpillar that emerges feeds exclusively on milkweed, absorbing the glycosides that milkweed contains. Butterflies retain the glycosides they absorb as caterpillars. Research on monarch butterflies whose migration has been tracked shows that the combination of glycosides in a butterfly always exactly matches the distinctive combination of glycosides that exists in the species of milkweed in the butterfly`s place of origin.