Pyrethrins are natural insecticides derived from the flowers of the chrysanthemum plant. They are effective against a wide range of pests, including mosquitoes, flies, and fleas. Pyrethrins work by attacking the nervous system of insects, leading to paralysis and death. These compounds are commonly used in household insect sprays and agricultural products due to their rapid action and relatively low toxicity to humans and pets. However, they can be harmful to beneficial insects like bees, so it's important to use them carefully and according to label instructions.