Nature Bulletin No. 256 February 12, 1983
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
Many of us have had the unpleasant experience of opening a bag of
corn meal or a package of cereal and finding it alive with squirming
weevils. These tiny grubs with whitish C-shaped bodies and dark
heads are the larvae of a Snout Beetle or Weevil. The adult is a small
inconspicuous dull-colored beetle with its head extended into a long
down-curving snout resembling the trunk of an elephant. This snout is
used by the female to drill holes in which the eggs are laid.
The weevils make up the largest closely-related family in the animal
kingdom. There are over 35,000 kinds, with more than 2,500 species
in the United States and Canada alone. All are strictly plant feeders
and most kinds prefer some special plant. Relatively few are injurious
to crops and those few are the most destructive insect pests known.
The most famous is the Cotton Boll Weevil which entered Texas from
Mexico in 1892. From there it spread until by 1922 it occupied
practically all of the cotton-growing region of the United States. It is
estimated that each person pays $10 per year extra for cotton goods
because of the damage this weevil does and the cost of fighting it.
The adults are about 1/4 inch long. After spending the winter under
piles of cotton stalks, dead leaves and trash, they emerge to feed on the
young cotton plants and mate. When the flower buds or "squares"
appear, the female uses the chewing jaws on the end of her snout to
drill a deep hole in the bud where she lays a single egg. After three
days, the egg hatches into a hungry white legless larva that devours
the inside of the "square" and kills it. The full-grown larva, about 112
inch long, is followed by a resting pupa stage, lasting 3 to 5 days, from
which an adult emerges to complete the cycle. There may be from two
to ten generations in a season, depending upon the locality and the
weather, and each female may lay from 100 to 300 eggs. The later
generations lay their eggs in the cotton bolls produced by those flowers
that bloomed, and their larvae destroy the bolls or injure them so that
few seeds, with the lint or fibers attached, can develop.
The Granary Weevil and the Rice Weevil ravage grain, flour and meal
in mills, elevators, ships, farms and homes, often causing total losses
in stored grains of all kinds. The adults of both beetles are about 116
inch long, dark brown or black, and have short snouts. Usually only
one larva feeds in each seed or grain, leaving only an empty hull. Both
regularly occur together and are much alike except that only the rice
The young of another weevil, the Plum Curculio, causes "wormy"
cherries, plums, peaches and other fruits with "stones", and also
damages apples. The adults become active about blossom time, mate,
and the females lay eggs in the newly formed fruits. As the larvae feed
and grow, they cause much of the fruit to drop before it is ripe, or
make it unfit for eating and marketing. The mature grubs leave the
fallen fruit to burrow into the soil where they become transformed into
another generation of little snout beetles distinguished by a shining
black hump on each wing cover.
The clover leaf weevil, the alfalfa weevil, the strawberry weevil, the
sweet potato weevil, and the sugar cane weevil -- to name only a few --
are other snout beetles which cause serious damage to crops. Last
summer. the hazelnut weevil ruined what had promised to be a record
yield. Another weevil with a very long snout attacks our hickory nuts.
The acorn weevil is common in the acorns of many oaks and is
relished by squirrels and woodpeckers.
The worms and weevils will get us yet.
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Update: June 2012