Post by Jen B

My family went on a bike ride last weekend at Ray Lake Forest Preserve. All afternoon, rain sputtered on and off as the clouds played tag with the sun. After climbing up a steep hill, the sky darkened again and we sought refuge under a canopy of large oak trees. One of my sons yelped,”Ouch! That raindrop hurt!” We quickly realized it wasn’t a raindrop, but a storm of acorns jiggled loose by the wind, plopping down on us. The trail became littered with acorns, and the kids began grabbing them. Upon inspection, the boys noticed tiny round holes in many of the acorns—evidence that these nuts were homes to acorn weevils (Curculio spp).

Acorns are a part of this weevil’s life cycle, serving double-duty for these little critters: food for the adults and a nursery for larvae. Acorn weevils are insects belonging to the family Curculionidae, commonly called snout beetles or true weevils. While their size is small, most measuring less than quarter of an inch, their numbers are mighty. Weevils are one of the largest families of insects worldwide.

Weevils have an extremely long, hollow snout with tiny jaws at the tip. Antennae are situated halfway up this long mouthpart at an angle, so as not to get in the way during dinner. They use this unusual mouthpart like a drill, chewing in circles until the acorn shell is pierced.

Adult weevils are hard to find. They spend early summer days at the tops of oaks, feasting on the liquid fat and sweet nut meat inside young acorns. Want to see this process in action? Take a look at this amazing footage from National Geographic.

A female weevil is careful not to eat too much from each acorn. Once she has gotten her fill, she lays a fertilized egg or two inside the acorn via the same hole. She then plugs the hole with a fecal pellet that dries and turns white. The eggs hatch a few days later into grub-like, white larvae with brown heads. The larvae feast and grow inside the acorn. As autumn arrives and the acorn rains begin, the weevils inside are signaled to make their move.

They escape by chewing a hole (or enlarging the hole their mother made) and slowly squeezing their plump bodies out. Exiting an acorn can take up to three days, during which time the larvae are an appealing snack for small mammals, spiders and other insects. Those that successfully emerge will immediately burrow underground, where they spend anywhere from one to three years before emerging as adults.

Acorns abound this year, and autumn is a great time to explore the Lake County Forest Preserves in Illinois. Pick up an acorn and see these critters, or signs of their presence, firsthand. Families will enjoy learning about acorns and other seeds along our new Trail Tales at Greenbelt Forest Preserve and Ryerson Conservation Area. The self-guided storybook trails offer nature education and exploration along with your hike.