The mosquito and black fly hatch generally starts at the end of May or the beginning of June. Black flies hatch in cold running water. They can be especially numerous if we have unusually warm weather during spring runoff, or when heavy rains keep streams high into summer. Large numbers of black flies are usually gone by July. Some years, the island has relatively few. In a heavy year, a few may linger until frost. The first frost may come as early as the end of August or as late as the end of September.
Mosquitoes usually get off to a quick start and then slowly taper down as the summer
dries out. In a rainy summer, they will stay at high numbers. At least some mosquitoes
will hang on until a heavy frost finally ends their season.
Insects are part of the natural scene at Isle Royale and they can be annoying.
The number of bugs and when they arrive varies considerably from year to year.
Insect numbers also vary from one location to another on the Island due to micro-climate
effects and from day to day due to weather changes. For example, the cooler
Lake Superior shores tend to have fewer mosquitoes, but wind direction and other
factors can override that tendency. Hot, humid weather brings out every available
mosquito and black fly. Cool, dry, breezy days slow them down.
When they are really out, they can be so thick as to drive campers to desperate measures such as spending lots of time in tents, using head nets and breathing through their teeth. At times, the conversation turns to modes of protection. Discussions of the merits of DEET repellents versus citronella repellents entertain some folks, while others securely cover all exposed skin on their bodies with bite-proof material. Do come prepared to protect yourself. Fortunately unlike mosquitoes, black flies do sleep at night.
Deer flies and horse flies are most prevalent during the warmer months.
Stable flies can be quite numerous during periodic hatches, mostly along shorelines. Long pants and thick socks are the best defense.
No-See-Ums come around from time to time during the warm part of the season. We haven't figured out any pattern to them yet. Make sure the zippers on your tent are closed really tight when they are around.
Mosquito: Most everyone knows what they look like, the flying hypodermic needle.
Black Fly: These look like overgrown fruit flies or a husky gnat, lots smaller than a house fly. Mostly teeth, they don't poke you with a needle; they chew a small hole to take a little blood. They love the backs of your ears and along the edges of clothing.
Deer Fly: The delta-winged B-1 bomber of the insect world. Some are quite colorful with green and orange markings. The most colorful are sometimes affectionately called "moose flies" on the Island. The most persistent of this species are capable of following the same hiker for miles often trying to land on the exact same place in the part of your hair every few seconds unless you persuade it to do otherwise. A hat also helps.
Stable Fly: Looks like a slightly undersize house fly (somewhat lighter in color) but the soft, blunt probe is missing (replaced by a retractable drill). They tend to stay close to the ground explaining one of their many names, "ankle-biter". Also known as the "fish fly", or "beach fly" for its favorite environment.
No-See-Ums: If you figure out what they look like you've got better eyes than us. You feel them before you see them anyway.
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