Insects, Spiders, Centipedes, Millipedes

Monarch butterfly resting on fern
Monarch Butterfly

NPS photo

The many terrestrial and aquatic environments at Pictured Rocks National Lakeshore offer great habitat where small creeping, crawling, swimming, and buzzing creatures can live and breed. Insects (along with their arthropod relatives the spiders, millipedes, mites, and tiny aquatic zooplankton) make up the bulk of the park's animal life.

Many visitors tend to notice insects only when swatting biting flies and mosquitoes, but beautiful insects abound as well. Keep an eye out for the many colorful butterflies, dragonflies, and damselflies found in this region.

Smaller, more secretive creatures like tiny beetles are less visible but just as interesting to observe. Look for insects on flowers, leaves, and tree bark. Slowly turn over a rotting log to see animals usually hidden from view – but make sure to carefully replace the log again!

Ecological Importance
The important role of insects is clear to scientists. Bees and flies function as pollinators, and scavengers like beetles break down dead plant and animal matter. High numbers of many species such as mosquitoes provide food for bats and other hungry creatures. Insect monitoring at the lakeshore has primarily focused on aquatic insects and larvae as they are good indicators of water quality. The presence of mayfly, stonefly, and caddisfly larvae in the lakeshore's cold fast-flowing streams indicate that these waters are in good ecological health.

Studies of aquatic life in the park's inland lakes have identified more than 100 taxa of benthic (bottom sediment) organisms. These include representatives of water bugs, water beetles, caddisflies, butterflies, dragonflies/damselflies, mayflies, fishflies/alderflies and true flies. The benthic communities in the shallower, near-shore areas show more diversity than the deepest regions of the lakes.

Pictured Rocks is one of several parks involved in a regional NPS study to detect the presence of mercury in aquatic environments by sampling dragonfly larvae. Information from this study will help scientists understand how mercury in northern lakes spreads throughout the aquatic food web.
Small bright red maple bladder galls dot the surface of a green maple leaf.
Maple Bladder Galls

Richard Orr photo

What's On That Leaf?
As you walk through the forest, you may notice strange colored bumps or projections on certain tree leaves, particularly maple leaves. These bumps are galls, plant growths stimulated by the activity of a specific insect. On maple leaves, small red bumps are caused by the tiny maple bladdergall mite, while the maple spindle gall mite initiates pale-colored spiky growths.

Feeding or egg laying by the insect produces a chemical stimuli that prompts the plant to create a small sac or "cocoon" around the insect. This relationship is wholly beneficial to the insect, as it can feed and grow inside this protected shelter until it is ready to leave. Large numbers of galls on a tree can be detrimental, but generally their impact on plants is benign.


Non-Native Insects
Non-native insects include many invasive pests that threaten ecosystems, local wildlife and human health. At Pictured Rocks, one of the most serious invasive pests is the beech bark scale insect that causes Beech Bark Disease. This disease is killing most of the mature beech trees in the national lakeshore and throughout the Upper Peninsula. The loss of beech as an important component of the forest canopy will affect many species of wildlife and the forest community as a whole.

Other harmful non-native insects include the emerald ash borer and spongy moth (formerly gypsy moth). The park is also monitoring the advance of destructive forest insects such as Asian long-horned beetle and hemlock wooly adalgid, invasive species that are moving towards Michigan from the east and south.

Outbreaks of native insects that feed on trees, such as cankerworm, occur from time to time. Their "boom and bust" cycles are natural parts of forest life. Unlike exotic pests, native insects have a well-developed army of natural enemies that keeps them in check for long periods between outbreaks. However, in forests already stressed by invasive pests, drought, climate change, and other factors, eruptions of native insects can have a drastic negative impact on tree health.


Last updated: September 9, 2022

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