The Phantom Midge Returns: A Lake Mendota Mystery on Ice

Before ice season melts completely away on Madison’s lakes, we wanted to share some really cool photos that local ice angler, Jim Kusuda, took when he was fishing in 70 feet of water on Lake Mendota back in February. What, Kusuda, wanted to know, were all these “white worms” turning up in his fishing holes?

Readers of this blog may be familiar with what is often referred to as the “phantom midge.” No, we don’t mean the ephemeral CFL house band, we mean the genus of midges (or lake flies) called Chaoborus. Before they are tiny flying insects swarming shoreline airspace, they are tiny, nearly transparent larvae living down in the lake sediment.

Lake Mendota used to have an incredible phantom midge population – samples taken in the first half of the 1900’s found densities of as much as 20,000 midges per square meter of the deep-water lake sediments. But, sometime in the 1950’s phantom midges basically ghosted Lake Mendota. They just stopped showing up in lake sediment samples or, if they did, they were in extremely low abundances.

But, thanks to Kusuda’s picture, we can say with some certainty that, well, the phantom midge is back – at least for the winter of 2022/23!

One of Jim Kusuda’s ice fishing holes filled with the tiny, white bodies of Chaobrus, or “phantom midge’ larvae. Photo: Jim Kusuda

Dick Lathrop, a retired research scientist with the Wisconsin Department of Natural Resources, spent a lot of his career familiar with the tales of the once abundant phantom midge. “[Phantom midge] densities were down some when the blood red midges (Chironomus plumosus) were abundant in deep-water bottom samples of the 1950s during the perch ‘heydays,'” of Lake Mendota, Lathrop says.”Then in samples from the mid-1960s and late 1980s, both midges were found in very low densities in Mendota’s deep-water sediments.”

But, Lathrop says, “in the past couple of decades, both midges seem to have rebounded.”

In related news, Kusuda sent in the following photo a couple of weeks after his February find along with a note that fellow ice anglers had “quite a few reports of cisco being caught through the ice.” Kusuda also reported that he had been catching nice batches of perch up to twelve inches long this winter.

“I think a major point of this story is that both cisco and perch are apparently doing well in Lake Mendota, and the return of good densities of midges – both the phantom midge and chironomid midges – is a good food source for the fish,” Lathrop says.

One benefit of an increase in midge populations, has been more food for popular sportfish species like yellow perch. Photo: Jim Kusuda

As for the question as to why the midges might be coming back, Lathrop says that he asked that question back in 1992 in a few scientific publications he wrote. His speculation then was based on three reasons: summertime “dead zones” in the deep water that led to low-oxygen (anoxic) habitat with higher sulfide and ammonia concentrations in lake sediments, potential impacts of pesticides washing into the lake, and increased densities of common carp, an invasive species introduced to the lakes decades ago.

Lathrop says he wasn’t sure which hypothesis could help explain the mystery, and it could likely have been a combination of factors. But, in 1989, the Wisconsin DNR, did a whole-lake complete fish kill, using a chemical called rotenone in Delavan Lake which had an extremely over abundant carp population. Before that project, densities of midge larvae and, really, any invertebrates living in Delavan Lake’s bottom sediment were very low but, Lathrop says, after the fish kill, populations exploded.

“This experience on Delavan made me believe that carp were the culprits for the decline on Mendota in the 1960s,” Lathrop says. He also notes that, in recent years, there has been a lot of work to lower carp numbers in Madison lakes, as well as the outbreak of what’s called “koi hemorrhagic septicemia virus” which can kill carp.

Did the carp population crash in Mendota?  Lathrop says he doesn’t know, but he “just can’t come up with any better explanation.” Besides, he’s retired. Now it’s just another mystery for our North Temperate Lakes Long-Term Ecological Research scientists to figure out!

Whatever the reason, we’re glad the phantom midge is back. And so are cisco and yellow perch and the ice fishers like Jim Kusuda who made all sorts of unexpected finds through the ice this winter.