Natural Curiosities

Q. A flock of flies seems to congregate around the deck at our Le Sueur County lake cabin on summer evenings. The insects circle each other at distances of 2 or 3 inches until it begins to get dark. This must take a fair amount of energy, but I can't imagine anything they receive in return. Why do they do it?

Jim Nessa
St. Paul

A. They're probably chironomids—nonbiting midges—with their sights set on making more chironomids. According to University of Minnesota entomologist Len Ferrington, male chironomids gather in a tight swarm, then mate with females that fly into the swarm. Ferrington says a swarm contains hundreds or even thousands of individual midges, and often forms near a dark background or an area of polarized light (such as reflections off water).

Q. I'm curious about the pile of boulders about two miles offshore in the southern portion of Mille Lacs Lake, observable from U.S. 169. My dad called it Spirit Island in the 1930s and '40s. I think it may be a federal game refuge now. Do you have any information on its origin?

James Marshall
Grand Rapids

A. DNR geologist Heather Anderson says Spirit Island is a boulder lag—a pile of rocks left by a retreating glacier. The rocks were part of a large pile, or knob, of debris deposited by the glacier more than 10,000 years ago. Over time, wind and water eroded sand, gravel, and other finer materials, leaving just the big boulders.

In 1915 Spirit Island and another Mille Lacs rock pile known as Hennepin Island became the Mille Lacs National Wildlife Refuge—the smallest NWR in the United States, according to Rice Lake NWR manager Mary Stefanski. Herring gulls, ring-billed gulls, and double-crested cormorants nest on Spirit Island. Hennepin Island is a nesting site for state-threatened common terns.

Q. We have a large maple tree in our back yard. Last summer I observed a gray squirrel biting through small branches and letting them fall to the ground. My neighbors have the same type of maple but the squirrels never bother it. Why is it clipping our branches?

Jeffrey S. Meyer
St. Paul

A. DNR wildlife biologist Bob Welsh suspects it was after the sugary sap that oozes out of fresh tree wounds. Why your tree and not the neighbors? Something was making your sap better. It could be a difference in fertilizing or watering. Or perhaps your tree was in the process of setting seeds and so had intensified sap flows.

Q. One late spring day we watched a raccoon climb a tree over our fishing boat at our home near Milaca. The raccoon climbed onto a branch, straddled it, and stayed there. We noticed hundreds of wood ticks of every size falling off the raccoon. (And right into our boat!) The raccoon stayed for several minutes as if in a trance, then climbed down and left. Can animals lower their body temperature enough to fool ticks into leaving?

Deb Killmer
Cold Spring

A. DNR wildlife educator Jan Welsh suspects the raccoon's sluggish behavior was due to illness, perhaps the later stages of distemper, rather than to the tick infestation. Pretty much all wild mammals are full of ticks, and the ticks naturally fall off when they become engorged with blood. The raccoon's trip up the tree might have dislodged more ticks than usual.

Q. I have seen robins and a house sparrow with a couple of white feathers. Is this a sign of old age, or something else?

Constance M. Van Valkenburg
St. Paul

A. These birds have partial albinism, meaning that some of their normally pigmented feathers lack pigment. Birds grow a new set of feathers each year, so age doesn't affect feather appearance.

Q. I have seen a piebald fawn buck. He has lots of white on his nose, legs, hind end, and the top of the head. How many have been seen in Minnesota?

Bud Watkins
Cloquet

A. Not many. Piebald (two-toned) deer are mottled white and brown. The piebald is one of several inherited variations in coloration found in white-tailed deer, says Christopher DePerno, DNR deer project leader. Albino (white) deer completely lack the pigment melanin. Melanistic (black) deer have more melanin than usual. All three conditions are rare, affecting fewer than one in 100 deer. Piebald white-tailed deer sometimes have malformed legs, noses, jaws, spines, or internal organs.