If you take a close look at the Black-eyed Susan blossoms that can be found in unmowed fields and roadsides this time of year, chances are good that you will find a tiny beetle called a weevil. A weevil’s mouthparts are formed into a long snout, with one antenna on either side of it. The snout is used not only for feeding but also for making cavities in buds, fruits, seeds, stems, and roots of plants, where eggs are laid. When the weevil larvae emerge, they feed within the plant.
There are 60,000 species of weevils, all of which are herbivorous and most of which are less than ¼ ” long. Most of those found on Black-eyed Susans appear to be feasting on pollen. Many weevils are pests of plants such as cotton, alfalfa and wheat. You may have even found them inside your house devouring your cereal or flour.
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Weevils are a type of herbivorous beetle which belong to the family Curculionidae. There are more species in this family than in any other beetle group – over 1,000 species in North America alone. Most weevils are small (3mm-10mm in length) and are usually dark-colored. Their most distinctive feature is the shape of their elongated head which forms a snout with their mouth at the tip.
Black vine weevil larvae overwinter in the soil. In the spring, the flightless adults emerge and feed at night on the outer edges of leaves, causing the leaves to have a notched margin. They mate and lay as many as 500 eggs in the soil near the base of host plants. The larvae hatch in a week or two and feed on plant roots until cold temperatures drive them further underground. The larval stage is quite destructive, especially to landscape plants such as rhododendron and azalea. Female black vine weevils have the ability to reproduce parthenogenetically. Fertilization of eggs is required to produce males, but no males have been observed in North America. (photo: adult black vine weevil on Jack-in-the-Pulpit fruit)