Sunday, October 15, 2017

Acorn Weevil

Acorn Weevils in the genius Curculio can be deceptively difficult to tell apart as they all look similar and have similar lifecyles. However, I believe this one is Curculio glandium. These tiny weevils measure up to 3/8ths of an inch or somewhere between 4mm and 10mm. They range in color from brown to brownish-gray with a somewhat mottled appearance. The distinctive characteristic is the oversized snout, or rostrum as it is referred to. It is easily twice as long as the body. The antennae are attached to the snout and they have large "buggy" eyes. They have a muppet-like appearance making them one of the most adorable beetles in the insect World.
 I KNOW, we aren't supposed to use words like adorable, or cute when describing insects (or any animal) as this anthropomorphizes them, but I'm okay with that.

I find them frequently at the white sheet and mercury vapor light that I put out each evening during the summer months. We have a lot of Burr Oak trees near our crop fields and close to an old pond that dried up. I am assuming the large number of acorn weevils are in direct relation to the amount of oak trees we have.

The female will use the modified tooth-like structures at the end of her snout to chew into the acorn (or depending upon species other tree nuts) and have herself a little meal before depositing a single egg inside.

Once the egg is safely planted inside the acorn, it will hatch and feed on the nut meat inside. Sometime in late fall or early winter the acorns begin to fall from the trees and this seems to signal the larva to begin chewing out of the nuts. Maybe it is the sudden jarring of the nut hitting the ground and a good sound thump to the head that lets them know it is time for the next phase of their development. The tiny white weevil grubs will then burrow into the soil as quickly as they can to avoid any predators that are keeping an eye on the acorns for just such an emerging snack. Once underground they are relatively safe from harm and can finish out their development to the adult form, which can take anywhere from one to as long as five years. I suppose temperature plays a large role in how long this final stage lasts.

The adults will emerge in the spring and mate soon after, and then the cycle will start all over again.
Acorn weevils are found throughout most of the United States and
portions of Canada. 

The feeding habits of these weevils will not cause any damage to fully grown oak trees. However, if there are large infestations of these beetles it may drastically reduce the amount of acorns capable of developing into trees. This will result in fewer trees.

There are two types of acorn weevils, the long-snouted variety in the genus Curculio (Pictured here) and the short-snouted variety in the genus Conotrachelus. The short-snouted variety have a little different lifecycle. Instead of the female chewing into fresh acorns and laying an egg, they will use acorns that have already dropped to the ground and have existing cracks.

If you are a forager and like to collect acorns for human consumption you will have to be quick to gather your harvest. The acorns that have been consumed by weevils will be left untouched by squirrels as they seem to realize there is not enough nut meat to be worth the effort it would take to collect them and bury them. So they go straight for the good nuts that have fallen from the trees and bury them at a record pace. If you find nuts that are lighter in weight and with a single tiny hole those are empty or "bad nuts." It is not uncommon to find some nuts with weevil larva in them, these nuts will often be "moving, or "jumping" like Mexican Jumping Beans as the larva moves around inside them. It is almost as if they are restless to escape their chamber and get on with the next phase of their lifecycle.

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