How to identify acorn weevils

acorn weevils

Most people will never have a chance to observe the adult acorn weevil unless they climb high in an oak tree to search for this minute beetle like insect that is often no larger than one fourth inch long. But the evidence that this insect is present can often be found in the acorns that fall from the oak tree. Found in the Coleoptera order of beetles, the acorn weevil is in the Curculio genus of the Curculionidae family. These tiny insects can be found throughout the world in areas where oak trees are growing.

The body of the adult acorn weevil is somewhat oval shaped with long slender legs that are jointed with gripping feet like appendages. The head of this amazing little insect has a snout projection with its mouth at the end. In some species these projections are almost as long as the body of the acorn weevil. The antennae extend from the snout and are jointed, bending first back toward the head with a longer extension facing away from the head. Acorn weevils use their beak-like extended mouth parts to chew through the outside shell of the acorn.

This is done in a drilling fashion that gives the insect access to the meat of the nut inside, which they feed on. The best way to observe one stage of the acorn weevil’s life is to pick up acorns that have dropped from the oak tree. Look for tiny holes in the outside shell of the acorn. Once you find these tiny holes, gently squeeze the acorn to see if they have a somewhat soft feeling. Both the tiny holes and weakness in the outer shell of the acorn, are usually signs that the acorn weevil is present in one stage or the other. To determine if the larvae are present, gently break open the acorn and study the insides.

If the acorn weevil larvae are present you will see a minute worm-like creature that has no legs. The inside of the acorn will be in some stage of deterioration from the larvae feeding on the nutmeat. Be sure you do not mistake the acorn weevil larvae for the acorn moth larvae. This insect is a tiny moth that also deposits its eggs inside the acorns, which are being fed on by acorn weevils. When the eggs hatch the acorn moths larvae, like the acorn weevil larvae, feed on the insides of the acorn usually remaining there until the following spring.

One of the most interesting facts about the acorn weevil is their egg laying process. The adults mate during the early summer months, high in the oak trees. Once the females are fertilized they will deposit their eggs in tiny chambers in the new soft-shelled acorns that have been drilled with their amazing snout. When the eggs are deposited, the female will close the opening with a fecal plug to protect the eggs.

The plug dries, turning white in color, keeping the eggs and larvae safe from predators. When the eggs hatch the larvae feed on the soft insides of the acorn until the nut drops from the tree. Once the larvae have matured they will drill an exit hole out of the acorn and burrow in the soil near where the acorn has fallen.

Interestingly, most larvae remain in the soil for up to three years before they pupate during the spring. New adult acorn weevils appear in early summer, crawling up the base of the oak tree to begin feeding and mating.

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