A Weevil is any beetle from the ‘Curculionoidea’ superfamily. They are usually small, less than 6 millimetres (¼ inch) and herbivorous. Due to the shape of their heads, weevils are commonly known as ‘snout beetles’. The adult weevils have a snout and are about one-fourth inch long.
Weevil beetles may be reddish-brown, grey, or almost black in color.
A distinguishing feature is the presence of two spurs on the first joint (femur) of each front leg.
There are over 60,000 species in several families, mostly in the family Curculionidae (the true weevils). Some other beetles, although not closely related, bear the name ‘weevil’, such as the ‘Biscuit Weevil’ (Stegobium paniceum), which belongs to the family ‘Anobiidae’.
Many weevils are damaging to crops. The ‘Grain Weevil’ or ‘Wheat Weevil’ (Sitophilus granarius) damages stored grain. The ‘Boll Weevil’ (Anthonomus grandis) attacks cotton crops. It lays its eggs inside unripe cotton bolls and the young weevils eat their way out. Adult Boll Weevils spend the winter in ground trash near old cotton fields. Eggs are laid singly in squares and bolls in punctures made by the weevils snout.
Feeding punctures appear as small uncapped holes, whereas egg-laying punctures are covered with a small wart-like growth. Both types of punctures will cause squares and small bolls to drop. The white, legless larvae feeds and pupates within the square or boll. The development from egg to adult takes 3 weeks. During the growing season the adults emerge from the square or boll, however, some adults of the previous generation may remain in bolls during hibernation.
Weevils are often found in dry foods including nuts and seeds, cereal and grain products. In the domestic setting, they are most likely to be observed when opening a bag of flour although they will happily infest most types of grain including oats, barley and breakfast cereals. If ingested, E. coli infection and other various diseases can be contracted from weevils, depending on their diet.
Because there are so many species and such diversity, the higher classification of weevils is in a state of flux. Weevils are generally divided into two major divisions:
- The ‘Orthoceri’ or primitive weevils
- The ‘Gonatoceri’ or true weevils (Curculionidae)
Primitive weevils are distinguished by having straight antennae, while true weevils have elbowed (geniculate) antennae. The elbow occurs at the end of the scape (first antennal segment) in true weevils and the scape is usually much longer than the other antennal segments.