Female Acorn Weevil (Conotrachelus posticatus)
Identifying this bug is relatively easy with that long snout! That snout is known as a proboscis which they use to chew their food. The Weevil in my photo above is an adult female.
During the spring, the female adults will lay their fertilized eggs into young acorns. Young acorns still have a soft outer shell which allows these bugs to lay their eggs in them.
Come mid-summer; the acorns begin to grow. While they are growing, their outer shell is also hardening. At this time, the eggs will hatch into grub-like larva that will feed on in the inside of the acorn.
In the Fall, the acorns begin to fall to the ground. At this point, the grub-like larva slowly chew a perfectly round hole about 1/8 inch wide which they will use to make their way out of the acorn. Because the shell has entirely hardened by this point, this is a lengthy process that will take the rest of the Fall season.
Fall has passed, and winter has begun, and those grubs have finally chewed a hole big enough for them to leave the acorn. Once out of the acorn, they will burrow themselves into the soil, which is where they will be for the next one to five years. Being underground helps keep them safe from predators that would love to eat them as they are a protein-packed snack for other insects and mammals such as spiders and skunks. They will emerge from the ground as full-grown adults (as seen in my photo), and the process will be repeated.
As adults, these bugs become a huge target for the Weevil Wasp (Cerceris spp), which are lone hunters that only prey on Weevils. Like the Tarantula Hawk, these wasp use these weevils as a food source for their larva.
One of the first questions I get asked after identifying a bug is, is it harmless to my plants and trees. Well, rest assured that these bugs are harmless to your plants and existing trees. Because of their larval diet, they can have an impact on new oak trees sprouting. The acorns that the larva are eating are the seeds of the oak tree. Once the larva has eaten the insides of the acorn, it can longer sprout into an oak tree.
Author: Dave Zeldin