Lake Ovid in Sleepy Hollow State Park in Clinton County has always been known for its good fishing and abundant aquatic plant life.

Located in a part of the state where there are few inland bodies of water, Lake Ovid is especially popular with mid-Michigan anglers who fish its 410 acres for largemouth bass, bluegills, redear sunfish, black crappies, muskellunge, catfish and yellow perch.

With a maximum depth of only 18 feet, light can penetrate to the bottom throughout the lake. And being located in an agricultural watershed provides plenty of nutrients for aquatic plant growth.

Normally, such abundant plant growth is not a problem, but two aggressive exotic species, Eurasian water milfoil and curly-leaf pondweed, have become well-established in the lake, creating dense vegetation mats and crowding out native plants.

According to surveys conducted by the Department of Environmental Quality, the problem grew steadily worse from 1995 through 2005.

The increase was not surprising to staff of the Department of Natural Resources, given the Eurasian milfoil's ability to quickly spread via small cuttings. On the other hand, curly-leaf pondweed grows aggressively during the spring and early summer but dies out by mid-summer.

Although park officials wanted to establish a control program for both species, they decided to target the Eurasian milfoil first, since this plant is causing more problems for boaters and anglers throughout the summer.

"Many people fishing at Lake Ovid had difficulty traveling the lake and catching fish because of the heavy weed growth in some areas," said Park Supervisor Tim Machowicz.

Traditional methods of Eurasian milfoil control involve the use of aquatic herbicides.

"But we were concerned that not only would these herbicides be prohibitively expensive, they also would lead to a very quick kill of the milfoil that could cause an oxygen deficit in the lake and trigger a fish kill," said Amy Harrington, fisheries biologist for the Southern Lake Michigan Management Unit.

Instead, biologists decided to try biological control as a more gradual approach to solving the milfoil problem.

"Being good stewards of our natural resources, anglers likewise prefer the use of natural control methods of invasive species whenever feasible," Harrington said.

The control of choice was Euhrychiopsis lecontei, the scientific name for the milfoil weevil, which is a native insect that normally feeds on native Northern milfoil plants.

From 1986 through 1989, a lake in Vermont "mysteriously" had a large die-off of Eurasian milfoil and it was discovered that little E. lecontei was to blame.

It turns out that the little weevil, no bigger than a sesame seed, actually prefers Eurasian milfoil to native milfoil species.

"Although adults also eat the plant, most of the damage actually is done by their larvae," Harrington explained. "Weevils lay their eggs on the growing tip of the plant. When they hatch the larvae burrow into the stem of the plant, eating as they go."

Harrington said this weakens the stem so much that the plant collapses to the bottom of the lake.

In July 2006, a team of DNR Fisheries and Parks and Recreation personnel stocked 23,000 weevils at six different sites around the lake.

"Within a month damage to the milfoil plants could be clearly seen," Machowicz said. "Milfoil plants were collapsing, leaving room for native coontail plants. Both adults and larvae were abundant in the stocked areas."

Earlier this year, 14,000 more weevils were stocked around the lake. The effort was funded in part by a grant from The Bass Federation.

A survey done at the end of July showed that though the milfoil is still the dominant plant species, it is far less abundant than it was in 2006 and most of the milfoil beds are showing signs of damage from the weevils.

"The weevils are spreading themselves throughout the lake," Harrington said. "I am finding them in locations that have not been stocked."

DNR biologists say it likely will take a few more years to bring the milfoil under control but this bio-method of eliminating an undesirable species is off to a good start.

"Anglers and other visitors that frequent Sleepy Hollow are talking about the 'bugs' that are eating the weeds, and they can already see a difference," said Lynne Thoma, an education and outreach technician with the DNR Fisheries Division.

So, if you notice these tiny weevils on your next visit to Lake Ovid at Sleepy Hollow State Park, please don't call insect control.

An eco-friendly army of weevils is on the attack in this weedy wonderland, a tactic the DNR hopes could be used in other lakes to remove an unwanted invasive species.