Remarkably, tiny insects survive weeks and months of sub-zero cold each year. This post provides brief descriptions of how three common bugs manage this; Woollybear Caterpillars, Mosquitos, and Ticks.
Woollybear Caterpillar (Pyrrharctia isabella)
The woollybear hatches in the fall and overwinters in its caterpillar form, when it nearly freezes solid. Their bodies produce glycerol, a fluid that acts like antifreeze to product their organs from being damaged by freezing. Woollybears thaw in the spring and metamorphose into the Isabella Tiger Moth. To compensate for short growing seasons, the closely related arctic woollybear lives through several winters before changing into the moth.
Mosquitos (Order Diptera, Family Culicidae)
There are 51 species of mosquito in Minnesota, ~24 of them bite humans. Winter survival strategy varies among the species, but most survive as eggs laid in soil. These eggs enter a dormant state known as diapause in response to colder temperatures and shorter days. Eggs in diapause do not hatch until environmental signals are detected, like increased temperature or increased moisture. Typically a consistent temperature above 50 degrees Fahrenheit is needed before mosquito eggs hatch.
Ticks (Family Ixodidae)
There are about a dozen species of ticks in Minnesota, the two that are most common and of concern as disease carriers are the American dog tick or wood tick (Dermacentor variabilis) and the black-legged tick or deer tick (Ixodes scapularis). Ticks have eight legs, and so are actually arachnids (like spiders), not insects.
These Minnesotan ticks are quite resilient to cold temperatures. The American dog tick is typically not active below 45 degF, but the black-legged tick is quite active as long as temperatures are above freezing. Both ticks survive the coldest temperatures by staying beneath cover, like leaves, near to the ground. Even in bitter cold snaps, near the ground temperatures are usually warm enough for these ticks to survive.
American dog ticks are carriers of Rocky Mountain spotted fever, while the smaller black-legged ticks are the main carrier of Lyme disease. Transmission of disease typically requires the tick to have been attached for more than a day. Frequent checking for ticks is recommended to help people avoid these diseases.
Ticks position themselves at the tips of low-lying grasses and bushes, waiting to grab onto passing animals or people. So, their “landing spot” is usually near ground level. They crawl up to find an exposed spot to attach. Therefore, use of a repellent like permethrin on shoes, socks, and pant legs can be an effective guard against ticks.
The tamarack is unusual because it is the only conifer native to Minnesota that is not evergreen. The photos below show how local tamaracks have changed color from September to October prior to dropping all their needles.
A disadvantage for deciduous trees is that they must expend considerable resources to make new leaves each year. During summer these leaves are very effective in capturing solar energy for the tree, but they are shed in fall because they are not suitable for winter. In contrast the leaves (needles) of evergreen trees are not as good at capturing energy in the summer, but they are made for winter survival and last several years before needing to be replaced. Plus, evergreen needles capture solar energy year-round.
Tamaracks have developed a survival strategy that is a mix of deciduous and evergreen traits. Like the evergreen conifers, tamaracks have needles. However its needles are “cheaply made” — thin, flimsy and not meant for winter survival. The open architecture of the tamarack tree maximizes the sun exposure for each needle, which somewhat compensates for the fact that the needles are only available to capture energy in the summer. Dropping needles is also advantageous to the tamarack because it helps the tree avoid structural damage caused by clinging heavy snow.
Another North American conifer that drops its leaves each fall is the Bald Cypress, the state tree of Louisiana. It is an interesting coincidence that both of these deciduous conifers prefer swampy environments. Perhaps a plentiful water supply is also key to their survival strategy?
Tamarack trees near Laporte, Minnesota are still green on September 23. Their characteristic scraggly form is evident in the picture on the left above.
The picture on the right above shows a tamarack beginning to turn from green to yellow. This tree is near the Shingobee River on the Paul Bunyan Trail, October 9.
Tamaracks that have turned yellow in fall are very striking trees. These tamaracks photographed on October 18 are near Williams Lake in Hubbard County, Minnesota.
Gentle snow fell in Northwestern Minnesota in early October this year, providing a wintertime preview. Surviving winter temperatures far below freezing is a big challenge for plants and animals. Today’s post focuses on how trees make it through — with some scenic pictures of the recent snow.
Trees are largely comprised of water, a critical issue for trees in the winter is to prevent water within living cells from freezing to crystalline ice. An important consideration is that most of the cells within trees are not living; freezing dead cells within trees happens commonly with no harm. Living cells avoid freezing by expelling water into the space between cells, increasing the sugar content of their remaining water, and transitioning this intracellular fluid to a viscous glass-like state.
Another winter-time issue for trees is water loss. To avoid excessive water loss, deciduous trees drop leaves with their large exposed surface area. Needles on evergreen trees minimize water loss because of their smaller surface area and their waxy outer coating.
Despite these coping mechanisms, extremely cold temperature does damage trees. If the water-bearing sap within trees freezes, the resulting expansion can literally cause trees to explode. Issues are also caused by swings in temperature. A warm spell, or prolonged sun exposure, can cause sap to flow, exposing the tree to damaging freeze in a subsequent cold snap.
Thanks to Tom Rongen for suggesting the topic of winter survival.
Staghorn Sumac (Rhus typhina) and Smooth Sumac (Rhus glabra)
Two species of sumac are widespread in Minnesota, Staghorn Sumac and the slightly more common Smooth Sumac. Staghorn Sumac bushes are larger, have fine hairs on their branches, and fuzzy fruit. The pictures below are likely a mix of Smooth and Staghorn Sumac.
The tart fruit of Staghorn and Smooth Sumac is edible, most commonly used to make a drink that tastes similar to lemonade. Leaves of Sumac turning brilliant red is an early sign of approaching fall.
Another species, Poison Sumac (Toxicodendron vernix) has noxious effects similar to Poison Ivy. It is found in Minnesota only in swampy areas in the eastern part of the state. In contrast to the other sumacs, Poison Sumac has smooth (not serrated) leaves and hanging clumps of fruit that are cream-colored.
Wild Honeysuckle (Lonicera dioica)
Wild honeysuckle is a native vine common throughout Minnesota. The pictures below show the interesting fruit of this vine first green, then later as it has ripened.
Bush honeysuckle species including Bell’s, Morrow’s, Tartarian, and Amur are non-native and regarded by the Minnesota Department of Agriculture as restricted noxious weeds.
Photographs in this posting show off fall scenery near Walker, Minnesota along the Paul Bunyan Trail, a Rails-to-Trails route between Crow Wing State Park and Bemidji (115 miles). This hilly and remote section of the trail, between highways 34 and 371, runs through the Chippewa National Forest.
Fir and Aspen
Annual growth is reflected by patterns seen in the branches of conifer trees. Robert Knudson, a local biologist, points this out in a terrific YouTube video about our Northern Minnesota conifers. Pictures in this post illustrate two of the patterns featured in his presentation.
Annual growth of Balsam Fir
The pictures above show buds of a Balsam Fir that are the starting points for next year’s new growth. Note that the buds are in groups of three.
Zooming out, the picture above shows how last year’s group of three buds at a tip of a branch (at the red dot) have grown out to produce three new branches. Each new branch has its own set of three buds at its tip.
Zooming out again, the picture above shows the pattern of annual growth in this Balsam Fir branch. The picture is annotated with alternating red and blue lines to indicate five years growth of this branch.
Annual Growth of Red Pines
Stands of Red Pine are shown in the pictures above. Note that branches are seen at fairly regular intervals along the trunks of the trees. Each interval between levels with branches reflects one year of the tree’s growth. The age of a Red Pine can be roughly estimated by counting the levels with branches along the trunk of the tree.
White and Jack Pines have the same growth pattern, but not as pronounced or regular as seen in Red Pines.
I noticed that this growth pattern is also evident in knotty pine tongue-in-groove panelling. As shown in the photos below knots in the wood are at regular spacings, reflecting yearly growth of the pine trees.
Interplay among three pigments is responsible for the changing colors seen in plant leaves each fall.
- Chlorophyll — this is the key green compound that enables the plant to convert sunlight and CO2 to sugar throughout the summer.
- Carotenoid — a yellow/orange compound that is present in the leaf throughout the year. When green chlorophyll breaks down in the fall leaves can take on the color of carotenoid.
- Anthocyanin — a red compound that is usually produced in fall when excess sugar is trapped in the leaf.
In response to longer fall nights, deciduous plants begin withdrawing sugars from their leaves and stop providing leaves with nutrients needed to maintain chlorophyll. The chlorophyll breaks down, which may turn the leaves the yellow color of carotenoid. Alternatively, a leaf may turn red because of anthocyanin created from trapped sugar.
Maple leaves with yellow, red, and green colors reflect different proportions of carotenoids, anthocyanin, and chlorophyll.
Hazelnut bushes in the two photographs above are directly across an east-west road from each other. The side of the road with the southern, sunny exposure has hazelnut bushes that have turned reddish. The other side with less sun, has bushes that have turned yellow.
The likely reason for the color difference is that leaves with more sun exposure contained more sugar, which transformed to red anthocyanin. Yellow carotenoid has colored the bushes that have had less sun exposure.
Color change is not restricted to trees. The image above shows a plant in the buttercup family, Early Meadow Rue, with fall colors. Its leaves with green centers and purple edges likely reflect the distribution of remaining chlorophyll and anthocyanin.
With fewer wildflowers in fall there is an opportunity to feature interesting flowers previously overlooked.
White Rattlesnake-root (Prenanthes alba)
White rattlesnake-root, also known as White Lettuce, is a shade-loving member of the aster family that flowers in the late summer. The plant pictured was in a wooded section of the Paul Bunyan Trail north of Hackensack Minnesota.
Native Americans used Rattlesnake-root for many medicinal purposes. In particular, the Iroquois used a poultice made from its roots to treat rattlesnake bites. There are also stories that juice from the plant is effective as a rattlesnake repellent.
Birdsfoot Trefoil (Lotus corniculatus)
Birdsfoot Trefoil is a plant in the pea family native to Europe. It has been purposely introduced in North America as a forage plant and as a control for roadside erosion, and is commonly seen blooming in our area from June to August. “Birdsfoot” refers to its seed pods that occur in clusters that resemble a bird’s foot.
While seed for this plant is still offered commercially as a cover crop, the Minnesota DNR considers it an invasive species that should be controlled. Dense mats of it choke out desirable native plants, which is of concern.
Butter and Eggs (Linaria vulgaris)
Butter and Eggs is an invasive species also native to Europe, with flowers similar to snapdragons . Yellow Toadflax is one of its many alternate names. It was brought to America as an ornamental plant, and because it was used to make yellow dye. It has spread aggressively to become an undesirable weed, mildly toxic to livestock.
Mullein (Verbascum thapsus)
Mullein was featured in a previous post, prior to its bloom. That post focused on the utility of its velvety leaves (Nature’s Charmin). But, it also has interesting flowers, as shown in the photo to the left.
Shelf-like fungal growths on trees are known as conks
Fungus identification is best left to experts, but I think the “conks” shown in the pictures above are the species Phellinus Tremulae. The photograph in the upper right is a close-up of the porous bottom-side of one of them. So far I have seen these growths only on the aspen trees locally called “popples”.
Phellinus Tremulae fungus is notorious for causing heartrot, which is the decay of the heartwood of live trees. This weakens trees, and aspens infected with this fungus are susceptible to toppling over in the wind.
Phellinus Igniarius is a very closely related fungus that is usually found on willows. I mention it because of a strange use. Alkaline ash produced by burning this fungus enhances the effects of natural plant alkaloid compounds, like nicotine and caffeine. Alaskan Native Americans mix tobacco with this fungal ash to make a concoction they call “iqmik”. Chewing it provides a dangerously powerful dose of nicotine.
Photographs in this posting show off fall scenery near Nevis, Minnesota along the Heartland Trail, a Rails-to-Trails trail for biking/running/walking that extends from Park Rapids to Cass Lake (49 miles). Also in our area is the Paul Bunyan Trail, a Rails-to-Trails route between Crow Wing State Park and Bemidji (115 miles).
The Rails-to-Trails Conservancy (RTC) promotes conversion of abandoned rail corridors to bike/running paths across the country. As a frequent user of these paths in Minnesota and other states, I’d like to advocate that people get out and use them. They are tremendous resources, and seem to me to be under-utilized.