Weevils

Weevils are a certain group of beetle falling under the superfamily Curculionoidea. Small herbivorous insects, most weevils measure around 6-15 mm long and 1-7 mm across. There are over 90,000 known species of weevil, making them one of the most diverse groupings of organisms in the animal kingdom. Because they are so many species, it is difficult to give a general description of weevils that completely captures their astounding diversity. Many species of weevil are known pests that can damage and kill crops. The grain weevil and boll weevil are two particularly destructive pests, feeding on wheat and cotton crops respectively.

The citrus root weevil Diaprepes abbreviatus. Credit: Wikipedia

Most weevils are covered in a chitinous carapace that is typically a shade of black, brown, orange, and yellow. Weevils are differentiated from other kinds of beetles in virtue of their snouts, which in some species can be as long as the body. The mouth consists of a pair of mandibles that they use to chew on crops and other vegetation. Like all insects, they have 6 legs, each tipped with a claw-like appendage for grasping and clinging to plants. Attached to the head are set of antennae used for sensory purposes. Some weevils have straight antennae and others have jointed antennae. 

Most species of weevil exhibit some form of sexual dimorphism, usually manifested in differences in size or snout length between males and females. In a particularly extreme case of dimorphism, females of the species Rhopalapion longirostre have a snout almost twice as long as those of males. The degree of sexual dimorphism reflects the environmental demands for reproduction.

The rose weevil (Rhynchites bicolor). Credit: WikiCommons

Weevils reproduce produce about 1-2 generations of offspring a year. In general, adults emerge in the spring where they go on to feed and look for a mate. After copulation, the female lays her eggs in sources of decaying vegetation; i.e. tree stumps, rotting logs, piles of dead leaves, and soil. Once the larvae hatch, they feed on the surrounding vegetation. One they have had their fill, they pupate and mature into adults over winter. When the next spring arrives, the adult weevils emerge and the cycle begins anew.

A larva of the weevil species Hyperia rumicus. Credit: WikiCommons

Weevils are voracious eaters and so can be a death sentence to yields of crops. The boll weevil, in particular, is known for the damage it causes by laying its eggs directly in the buds of cotton plants. In fact, it is estimated that from the years 1892-1993, boll weevil infestations cost cotton farmers in the U.S. south over $3.2 million a year—almost $90 million a year in today’s value.

Interesting Facts About Weevils

  • To date over 97,000 individual species have been named and cataloged.
  • Most weevils can fly due to wings tucked under their carapace.
  • The weevil Austroplatypus incompertus, is one of the only known insects other than ants and termites that exhibit eusociality, a social structure characterized by a rigid division of reproductive labor.
  • One species of weevil, succinctly named the “bird poop weevil,” (Mescalcidodes trifidus) has evolved to mimic the appearance of bird excrement.
  • The Polka Dotted Clown Weevil (Pachyrrhynchus orbifer) has a carapace covered in iridescent scales, giving it a spectacular rainbow like color.
  • Some insects called weevils are not really weevils at all. The biscuit weevil (Stegobium paniceum) is not a weevil, but another kind of beetle.