There are those who might say having your mouth inches away from the rest of your body is a horrible idea. The eastern acorn weevil would not be among them.
For this native Maine insect, having chewing mouthparts at the far end of its snout — otherwise known as the rostrum — is perfect for both feeding and reproduction.
The weevil’s rostrum is as long as its body and looks very much like an elephant’s trunk.
“That big long beak with the mouth parts at the end is pretty distinctive,” said Jim Dill, pest management specialty at University of Maine Cooperative Extension. “It’s such a funky mouth part.”
In Maine, the acorn weevil feeds almost exclusively on the acorns of oak trees. Even though a healthy population of the weevils can devour most or even all of a season’s acorn nuts, they do no damage to the actual trees. For the wildlife that eat acorns, the nuts are just one part of a varied diet. As far as insect experts are concerned, the weevils are a minor pest in the state.
The weevil uses its mouth like a drill to make a small hole in the acorn to access the fruit inside.
The nut inside may be a tasty treat for the female adult acorn weevil which also eats other vegetation including stems, leaves and flowers, but what she’s really after is a nursery room.
Once she drills the hole into the acorn, the weevil backs up to it and lays two or three eggs inside of it. She then plugs it up using her own fecal pellets.
Inside the acorn, the weevil larvae hatch and feed on the nut. When the acorns drop off the oak trees in the fall, the larvae chew their way out and go underground to spend up to three winters before emerging as adult weevils.
“It’s a pretty good strategy on their part,” Dill said. “If there is a bad nut year or the weather is not good in the summer, they don’t get wiped out.”
Luckily, the weevils have no real impact on the mature oak trees.
Because the grubs eat what’s inside the acorn but don’t harm the tree itself, they are considered minor pests, said Renee Hemmingway, Maine naturalist specializing in insects.
It’s a good thing because they would be difficult to control, since they are high in the trees and can’t be sprayed, Dill said.
Even though the weevils can destroy an entire acorn crop for the season, people really don’t mind, especially since they pose no danger to humans, Dill said.
“It’s a problem for people who want more oak trees or who want to see wildlife that eat the acorns,” he said. “But most people are happy they don’t have to keep pulling up oak seedlings.”
The acorn nut contains tannin which is toxic to humans, so it’s not a good idea to eat raw acorn nuts. They need to be toasted at 375 degrees fahrenheit for 15 to 20 minutes to be safe for human consumption.
For those who like acorn nuts, it can be disheartening to collect a bunch of them, only to discover many are hollow, compliments of the acorn weevil.
To determine if an acorn has a nut or not, you can put it in water — the hollow ones float.
Or, you could ask a squirrel.
“I once watched a squirrel run around collecting acorns [and] it would pick up the acorn and listen or shake it,” Hemingway said. “Then it would put it down or take it.”
When she went out to inspect the rejected acorns, Hemingway found every one of them had a small hole in the shell. Inside there was either a weevil larva or the mushy leftovers from a long-gone larvae’s meal.
“I had no idea back then that [acorn weevils] were the culprit and that squirrels had figured out how to determine if there was one inside,” she said. “It’s incredible.”