Nightcrawlers produce an average of 38 cocoons per year, or roughly one every 10 days, in the right conditions. Each cocoon may create one or two earthworms, although manure worms have as many as 11 worms per cocoon. Breeding rates of earthworms depend on soil conditions such as moisture, temperature, oxygen levels and available food. Pesticides and fertilizers reduce reproductive rates in worms because these chemicals alter the natural environment.
Earthworm species reproduce using two parents or one parent. Biparental reproduction involves the exchange of genetic material between parents, and then both worms carry cocoons. Biparental reproduction occurs only within the same worm species. In uniparental worms, the parent produces a single ovum that grows into a mature earthworm.
Pesticides and fertilizers cause long-term damage to nightcrawler populations, and colonies can take years to recover from pesticide contamination. Using minimal pesticides, spraying on dry days and buying less-concentrated pesticides keep chemical intrusions to a minimum.
Nightcrawlers reach sexual maturity after 350 days, but other species of earthworms reach sexual maturity after just three weeks. Nightcrawlers live up to six years in burrows nearly 8 feet deep. When colonies grow, nightcrawlers expand nine to 15 feet outward per year. Nightcrawlers do not have a dormant state as they simply burrow deeper in cold weather.