The boll weevil (Anthonomus grandis) is a beetle measuring an average length of six millimeters, which feeds on cotton buds and flowers. Thought to be native to Central America, it migrated into the US from Mexico in the late 19th century and had infested all US cotton-growing areas by the 1920s, devastating the industry and the people working in the American south. During the late 20th century it became a serious pest in South America as well. Since 1978, the Boll Weevil Eradication Program in the US has allowed full-scale cultivation to resume in many regions.
Adult weevils overwinter in well-drained areas in or near cotton fields after diapause. They emerge and enter cotton fields from early spring through midsummer, with peak emergence in late spring, and feed on immature cotton bolls. The female lays about 200 eggs over a 10-12 day period. The oviposition leaves wounds on the exterior of the flower bud. The eggs hatch in three to five days. The larvae feed within the cotton squares for eight to ten days, then pupate. The pupal stage lasts five to seven days. The life cycle from egg to adult spans about three weeks during the summer. Under optimal conditions there may be eight to 10 generations per season.
Boll weevils will begin to die at temperatures at or below 23 degrees Fahrenheit. Research at the University of Missouri indicates they cannot survive more than an hour at 5 degrees Fahrenheit. The insulation offered by leaf litter, crop residues, and snow may enable the beetle to survive when air temperatures drop to these levels.
Other limitations on boll weevil populations include extreme heat and drought. Its natural predators include fire ants, insects, spiders, birds, and a parasitic wasp, Catolaccus grandis. The insects at times engage in what seems to be almost suicidal behavior by emerging from diapause before cotton buds are available.
Boll weevils are featured prominently in dozens of blues, country, folk, and rock songs.