Nature & Science
Welcome to the Nature and Science Page!
Click on the links below to find out more about the Sawtooth National Recreation Area and what makes it so unique and special!
The Sawtooth National Recreation Area was established on August 22, 1972 and consists of 756,000 acres of beautiful mountainous scenery. The Sawtooth NRA includes the Sawtooth Wilderness, Cecil D. Andrus-White Clouds Wilderness, and the Hemingway-Boulders Wilderness areas. The Sawtooth NRA has over 700 miles of trails, 40 peaks rising over 10,000 feet and 300-plus high-elevation alpine lakes that add to the spectacular scenery and vistas.
For more information on the history of the Sawtooth NRA and Law 92-400 check out the About the Forest page.
Mountain Ranges: There are four mountain ranges located within the Sawtooth National Recreation Area. They are the Sawtooth, Smoky, Boulder and White Cloud ranges. Castle Peak is highest at 11,815 feet. Thompson Peak is the highest in the Sawtooths at 10,751 feet.
The Headwaters of the Salmon River: The Salmon River starts high in the snowy mountains as a small, meandering stream at the top of Galena Summit, and then winds its way down to the town of Stanley, gaining volume and making a 425 mile journey before it reaches the Snake River in Northern Idaho. The Salmon make this daunting 900 mile migration to the ocean and back during their lifetime. The Snake eventually meets up with the mighty Columbia River and returns to the Pacific Ocean. The Middle Fork of the Salmon, the Big Lost River, the Big Wood River, Boise River, and Payette Rivers all start on the Sawtooth NRA.
Lakes: There are four major alpine lakes located in the front country of the Sawtooth NRA. They are Alturas, Pettit, Redfish and Stanley. All of these lakes have camping, boating, fishing and hiking opportunities.
Want to know what makes the peaks so jagged? Check out the Geology section.
Looking for more information on wildflowers, let's Celebrate Wildflowers!
To find out about Non-Native Invasive Species and what you can do! For other Invasive Species Resources.
To find out about tree insects and diseases of the Sawtooth NRA. For more information on Forest Health and Protection
Want to go birdwatching, check out the bird checklist and see how many birds you can find!
Wondering what mammals, birds, reptiles, invertebrates, plants and fungi we have in Idaho, check out Natural Heritage.
If your looking for certain animals find out what habitat they live in below to know where to look.
If you see an animal and want to report a rare sighting, check out the Wildlife Orientation Checklist.
For more information on Endangered Species.
• 200 million years ago during the Paleozoic Era shallow seas covered the area creating the sedimentary rock of shale, sandstone and limestone.
• 110 million years ago during the Cretaceous period, the Pacific Plate subducted under the North American Plate and began to melt, intruding magma into a metamorphosed slate and marble. Folding and faulting of the metamorphic rocks.These intrusions created the deposits of minerals such as silver, gold, molybdenum and lead that miners sought in the 1880’s. Magma cooled 10 miles underground forming “plutons” of granite rock, granodiorite and quartz monzonite, known as the Idaho Batholith which is 200 miles long, 120 miles wide and 5 miles thick. The Idaho Batholith stretches across much of South-Central Idaho.
• 44-55 million years ago the Sawtooth Batholith rose. Magma was squeezed through the Idaho Batholith “cutting” into it and cooling. The Sawtooth Batholith is pinkish in color and 40 miles long. The Challis Volcanics occurred during the same time, where lava covered much of Central Idaho, depositing volcanic materials such as basalt and andesite.
• 35 million years ago the Basin and Range was formed with Fault Block activity and to this day this area is one of the most active seismic areas in the United States.
• 15 million years ago when the Sawtooth Fault lifted, and the Sawtooth Valley down dropped creating the sharp cliffs of the Sawtooth Mountains and flat Sawtooth Valley along with other water and ice causing erosion and depositing sediment into the valley.
• 2 million years ago during the many different Ice Ages or cooling periods glaciers would advance and retreat up to the most recent glaciation about 20,000 years ago. The glaciers carved out U-Shaped valleys (photo on right). Like a snowplow the glaciers pilled sediment on the sides (lateral moraine) and end of the glacier (terminal moraine) sometimes leaving lakes behind. In the valley floor as the glaciers melted glacial outwash was left behind. Large boulders that seem to be "out of place" were brought down by the glaciers and are called erratics. All the glaciers created the jagged peaks with their knife-edged passes, cirques, tarns, horns and arete’s leaving behind the Sawtooth skyline. Water in the forms of rivers and streams carved out v-shaped valleys, alluvial fans at the mouths of rivers, and through freeze/thaw created landslides, talus slopes and avalanches.
Weather and climate: The snowpack in the winter provides runoff throughout the summer and keeps streams and wetlands charged with water for habitats and ecosystems. Average snowfall is about six feet or more of snow in the winter with temperatures ranging from 9-29 degrees for the highs in the winter and 80 degrees or above in summer with it usually 70 degrees or below, and nights can be cold with possible summer frosts. For current Idaho Snow Water Equivalent from the National Resource Conservation Service (NRCS). For current avalanche conditions check out the Sawtooth Avalanche Center.
Air Quality: Without any cities or factories in sight the Sawtooth NRA has great air quality providing for crisp views of the mountain landscape and clean mountain air to breath in, unless there has been a fire in the area or nearby and smoke blows in.
Animal Habitats and Plant Communities
Animals and plants are adapted to the environment that they live in. Learn more about the different habitats we have in the Sawtooth NRA along with the different plants and animals that make their home there. Whether you enjoy looking for wildflowers, bird watching or looking for mammals, knowing where to look for which ones, is a great place to start!
Alpine Communities (Above 9500 feet)
The alpine communities are found at high elevations transitioning in upper subalpine forests and tree line with increasing elevation alpine communities end at the snow line where snow and ice persist through summer. Alpine plants are adapted to climatic extremes and harsh conditions such as strong wind, cold temperatures, ultraviolet radiation, and short growing seasons.
Plants: There are many grasses and sedges, flowers, cushion forming plants, dwarf shrubs, mosses and lichens that have developed strategies for living in alpine communities. Some of the common species are alpine bluegrass (Poa alpine), spike trisetum (Trisetum spicatum), Parry rush (Juncus parryi), blackroot sedge (Carex elynoides), pygmy bitterroot (Lewisia pygmaea), locoweed (Oxytropis spp.), little flower penstemon (Penstemon procerus), cushion phlox (Phlox pulvinata), alpine wild buckwheat (Eriogonum pryolifolium), snow willow (Salix nivalis), alpine laurel (Kalmia microphylla), mountain heather (Phyllodoce spp.), alpine spikemoss (Selaginella sppl), boreal pixie-cup (Cladonia borealis), and rockfrog lichens (Xanthoparmelia spp.).
Whitebark Pine (Pinus albicaulis), an Endangered Species Act Candidate species, grows on harsh sites in the upper subalpine forests and at tree line. On the Sawtooth NRA, whitebark pine grow with subalpine fir (Abies lasiocarpa), Douglas-fir (Pseudotsuga menziesii), Engelmann spruce (Picea engelmannii), or lodgepole (Pinus contorta). Some of these trees can occasionally exist above tree line as scattered individuals with truncated dwarfed growth form known as krummholz caused by the extreme wind and snow.
Wildlife: Mountain Goats and Bighorn Sheep are the biggest animals, while many small ones live amongst the rocks like Pika and Marmots. Wolverines also live in the Alpine communities, see more information about them below.
Birds: Horned Larks, Rosy Finches, and even Hummingbirds migrate along the high mountains in wet areas.
Forest Communities (6500-9000 feet)
Plants: Conifer forests on lower slopes and foothill moraines are dominated by lodgepole pine and Douglas-fir, with Engelmann spruce occurring on wet sites near springs or riparian areas. Ponderosa pine (Pinus ponderosa) occur on the west side of the Sawtooth NRA. It grows with Douglas fir and lodgepole pine. Above 7000 feet and up to tree line, subalpine fir and even higher whitebark pine occur.
Elk sedge (Carex geyeri), pinegrass (Calamagrostis rubescens), lupines (Lupinus spp.), valerian (Valeriana occidentalis), arnica (Arnica spp.) and grouse whortleberry (Vaccinium scoparium) are common understory plants in conifer forests.
Deciduous trees like aspen (Populus tremuloides) create biologically rich communities for birds and wildlife. Aspen typically re-sprout from the roots in response to disturbances, especially after fire and are an early succession tree. Aspens are one of the largest organism on earth because a whole stand of aspen can be just a clone of one tree. Each aspen stand can include one or more aspen clones. The aspen trees of a particular clone will change color in the autumn at the same time because they are genetically related. Autumn is the time to see where the different clones are located. Aspens do well near springs or seeps and black cottonwood (Populus trichocarpa) grow along the Big Wood and Salmon Rivers.
Birds: Gray Jay commonly called the “camp robber” because it steals food from your camp so make sure to keep a clean camp and don’t feed the wildlife; Clark’s Nutcrackers which has a close relationship with the Whitebark Pine because it reseed the Whitebark Pine when it cache or stores it’s food to eat later, but many times it forgets where it stores the food and new trees are grown; Steller’s Jays, Hairy and Downy Woodpeckers, Flickers and Sapsuckers among standing dead trees; Nuthatches and Creepers eat insects from live trees; and migratory Songbirds, and Sparrows to Kinglets to Thrushes.
Shrubland and Grassland Communities (Below 6500 feet - 9000 feet)
Shrubland communities include sagebrush and montane shrub communities. Shrubland and grassland communities occur in connection with forested communities and their locations are influenced by topography, snow pack, and soil moisture.
Plants: Sagebrush (Artemisia spp.) communities are an important recreation area, are the primary forage base for the western rangeland livestock industry, and provide water in a semi-arid region with one of the fastest growing human populations in North America. Sagebrush communities are considered to be among the most endangered in western North America with approximately a third of the pre-settlement area of sagebrush already converted to other land uses or highly degraded. On the Sawtooth NRA sagebrush communities are dominated by mountain big sagebrush (Artemisia tridentata ssp. vaseyana). Low sagebrush (Artemesia arbuscula), and black sagebrush (Artemesia nova) also occur in harsher conditions. Common plants growing with sagebrush are bluebunch wheatgrass (Pseudoroegneria spicata), Sandberg bluegrass (Poa secunda), wild onion (Allium ascalonicum), milk vetches (Astragalus spp.), buckwheats (Eriogonum spp), arrowleaf balsamroot (Balsamorhiza sagittata), and fleabanes (Erigeron spp.).
Montane shrub communities are interspersed as stringers and patches within the sagebrush, and forested communities. The patchiness of these communities is related to soils with high water-holding capacity and/or northerly exposures. Characteristic species include bitterrush (Purshia tridentate), chokecherry (Prunus virginiana), snowberry (Symphoricarpos spp.), serviceberry (Amelanchier sp.), wild rose (Rosa woodsi), and green rabbitbrush (Ericameria teretifolia).
Grassland communities are connected with shrubland, and forested communities. Their occurrence is related to soils and/or aspects. Typical grassland grasses are bluebunch wheatgrass, sandberg bluegrass, Idaho fescue (Festuca idahoensis), slender wheatgrass (Elymus trachycaulus), intermediate oatgrass (Danthonia intermedia), and needlegrass (Achnatherum spp.). Common wildflowers include arrowleaf balsamroot, yarrow (Achillea millefolium), lupine (Lupinus spp), biscuit root (Lomatium spp.), hawksbeard (Crepis spp.), fleabane, milkvetch, sego lily (Calochortus nuttallii), paintbrush (Castilleja spp.), and phlox (Phlox spp.).
Many of these areas have been grazed in the past. They include Mountain Big Sagebrush, Sagebrush, Fescue, Bunchgrass, Grasses, and Wildflowers. In wet spring areas you can find Arrow-Leaf Balsamroot, Lupine, Fireweed, Sego Lily, and Paintbrush.
Mammals: Pronghorns, Ground Squirrels, Coyotes, and Badgers.
Birds: Long-billed curlew, red-tailed hawks, Swainson’s hawk, northern harrier, golden eagles, vesper sparrows, Brewer’s sparrow, lark sparrow, and savannah sparrow, sage thrashers, Brewer’s blackbirds, and western meadowlarks.
Riparian and Wetland (near streams, rivers, and wet areas)
Riparian areas provide shade, shelter, and food for fish and wildlife, protect streambanks from erosion, help reduce flooding, increase water retention and provide clean water. These areas can be affected by grazing, mining, irrigation, diversion, development and recreational uses.
Plants: Riparian areas are lands that occur along water bodies like rivers, streams and lakes. Riparian communities can consist of of trees, shrubs, grasses and/or flowers.Common trees are subalpine fir, Engelmann spruce, and Douglas-fir, cottonwood, and aspen. Characteristic shrubs include Rocky Mountain maple (Acer glabrum), serviceberry, chokecherry, thinleaf alder (Alnus incana), currants (Ribes spp.), willows (Salix spp.), and shrubby cinquefoil (Dasiphora fruticosa). Grasses include sedges (Carex spp), tufted hairgrass (Deschampsia cespitosa), reedgrass (Calamagrostis spp.), timothy (Phleum spp.), and bluegrass (Poa spp). Common flowers include louseworts (Pedicularis spp.), American bistort (Polygonum bistortoides). saxifrage (Saxifraga spp.), stinging nettle (Urtica dioica), and fireweed (Chamerion angustifolium).
Wetlands are areas that form where water collects near the ground surface or where water moves slowly or not at all. Some plants that live in wetlands are camas (Camassia quamash), gentian (Gentiana affinis), edges, water-loving grasses, willows, alder, bog birch (Betula pumila), and red osier dogwood (Cornus sericea). These areas are important for amphibian reproduction.
Mammals: Moose, river otter, beavers and mink.
Birds: Cinnamon teal, common mergansers, osprey, bald eagles, kingfishers, sandhill cranes, spotted sandpiper, willow flycatchers, American dippers, song sparrow, fox sparrow, Lincoln’ s sparrow, red-winged blackbirds; yellow warbler, common yellowthroats. Some migrate through, while others stay longer to nest, and some like the American dipper stay year-round and catch macro-invertebrates in the winter.
Reptiles and amphibians: Garter snakes, western toads, long-toed salamanders, and Columbia spotted frogs.
Fish: Native Fish are Sockeye, Chinook, Steelhead Salmon, Bull Trout, Kokanee, West slope Cutthroat Trout, Wood River Sculpin, and Whitefish.
Species of Concern
The Sawtooth NRA is home to many species of concern that are quite a few “rare” and are classified as threatened, endangered, or sensitive.
The Sawtooth NRA has the following animals listed as endangered under the Endangered Species Act:
- The Canada lynx, a threatened species, requires large areas for its home range. Its preferred prey, snowshoe hares, thrive in mixed conifer-deciduous forests that are renewed by fire—a habitat that has declined across the West.
- Sockeye salmon (endangered), Chinook salmon (threatened), steelhead salmon (threatened), and bull trout (threatened) are all present in the Sawtooth NRA’s waterways.
The Sawtooth NRA has several sensitive species. These species are of concern by the Forest Service due to decline in their population or habitat quality:
- Mammals: wolverine, fisher, spotted bat, Townsend’s big-eared bat, pygmy rabbit, gray wolf, bighorn sheep
- Birds: greater sage-grouse, common loon, bald eagle, peregrine falcon, northern goshawk, white-headed woodpecker, northern three-toed woodpecker, boreal owl, flammulated owl, and great gray owl
- Amphibians: spotted frog
- Fish: west slope cutthroat trout and Wood River sculpine
- Plants: Whitebark pine
The Sawtooth NRA has many great lakes, streams and headwaters to offer for Salmon. There are Sockeye, Chinook, and Kokanee Salmon. Steelhead Trout which are also in the Salmonid family but are a type of Trout. They are all anadromous which means they spawn in freshwater streams, go to the ocean to grow, and return to fresh water as adults. The Sockeye Salmon who are also known as “redfish” rear in Redfish Lake causing the lake at one time to be red with fish. Sockeye are called “redfish” because of their brilliant red color and hook nose they develop when mating and spawning. After spawning they die and the new generation swims out to the ocean where they live for a few years and then return home.
In the end their migration would be 900 miles long which is the longest, furthest southern latitude and the highest elevation migration. The Chinook Salmon also known as King Salmon, named for the Chinook Native American tribe, are the largest Pacific Salmon. Steelhead also spawn in the large rivers and creeks, but they do not necessarily die after spawning and can go out to the ocean a second time if they have enough energy reserved.
Over the last 100 years there have been many barriers to their migration like over-fishing, dams, and habitat loss all along their migration route including the Sawtooth NRA, Salmon River and Columbia River. In 1991-1992 the Sockeye Salmon was listed as endangered. That year only one fish named “Lonesome Larry” returned from his migration. This is an example of how few fish return each year to the Sawtooth NRA after their 900-mile migration. The loss of nutrients from the fish along their migration is affecting different plants, animals and rivers. With help from the Fish Hatcheries and restoration efforts of the Sawtooth NRA we are working to help restore their habitat. To see some of these Salmon in action, check out the Sawtooth Fish Hatchery or the Hayspur Fish Hatchery.
Wolverine are another one of the Sawtooth NRA’s sensitive rare and fascinating animals. Not a dog or a bear the wolverine is the largest of the terrestrial weasel family which also includes short and long-tailed weasel, American pine martin, badger, fisher, and river otter. While thought to be solitary, research over the past few decades has shown that wolverines are quite social. Care of offspring by both parents is extensive. Their home ranges can be over 500 square miles and they can travel large distances. During a study in the Greater Yellowstone area, one GPS-collared animal was documented travelling 500 miles in two months. A male wolverine’s home range generally overlaps the home ranges of 2-3 females. He mates with those females and helps teach the kits how to be wolverines.
Wolverines are made for winter and cold climates with their long claws that serve as crampons, large feet and plantigrade stance that provide for good floatation on soft snow. They can gallop or lope on top of the snow traveling at quite a fast speed. Their compact body provides body-mass: surface ration designed for heat retention and their frost resistant guard hair was once used to line the hoods of jackets in the artic. Wolverines have scent glands (as do all mustelids) which cause their fur to smell and has led to one of their names, skunk bear. Each wolverine has a different marking on their chest which works like a fingerprint to tell their identity. Their teeth are razor sharp with molars facing 90 degrees towards the inside of the mouth and with their powerful jaw they can eat frozen meat, teeth and bones. They are great scavengers in winter and will stand up to any other predator who might want to fight it out over a carcass. Their scientific name Gulo gulo comes from the term “glutton” and they do eat as much food as they can when it is available but will cache extra food if they are unable to eat it all. They can smell a dead carcass buried even up to 20 feet below the snow making them the ultimate scavenger. They can even bring down a full-grown moose.
Wolverines are elusive and a rare sight to see. While there is still a lot unknown about their life history, the last few decades of research has indicated that due to their dependence on snow, especially for reproductive dens, the changing winter climates could affect them. Recent research has investigated how winter recreation impacts them. Check out the research report from 2018 and the published paper from this study, here.
While you are visiting the Sawtooth NRA you may catch a glimpse of a wolf in a field or hear their howls while you camp at night. Wolves are social, living and hunting in packs which generally consist of the breeding pair of alphas, and other family members. They are a keystone species meaning they affect all the other animals in the ecosystem. In the absence of wolves, a population of elk can become too high which then may affect the vegetation in riparian and wetland areas. Elk can overgraze the willows and aspen in these areas leaving less for the beavers to create the wetland areas. With the presence of wolves, elk populations levels are more compatible with the habitat.
Wolves were reintroduced to Central Idaho in 1995 and 1996 at the same time as Yellowstone National Park. They have come back quite well and were taken off the Endangered Species list in 2011. Idaho Department of Fish and Game manages wolves and hunting and trapping are allowed. For more information check out their websites: https://idfg.idaho.gov/conservation/wolf/management-history
Native species are plants and animals that have evolved in an area so that they are adapted to the local conditions and other native species. Exotic and invasive species is defined as a species that is:1) non-native (or introduced) to the ecosystem under consideration and 2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health. Invasive species can lead to the extinction of native plants and animals, destroy biodiversity, and permanently alter habitats. Invasive species can be plants, animals, and other organisms (e.g., microbes). Human actions are the primary means of invasive species introductions. Throughout the Sawtooth NRA history there has been farming, ranching, grazing, and recreation that can bring in exotic invasive or noxious weeds. On the Sawtooth NRA the most established non-native invasive plant species are spotted knapweed (Centaurea stoebe), yellow toadflax (Linaria vulgaris), rush skeletonweed (Chondrilla juncea), and cheatgrass (Bromus tectorum). If you are bringing stock into the area, make sure to follow certified weed and seed free feed for stock animals while in the Sawtooth NRA. Make sure to check the Alerts and Notices for stock use in wilderness areas.
In the rivers, lakes and streams the aquatic invasive of concern are: zebra mussels, water milfoil and other fish diseases. These can be transported by watercraft and even from boots. Make sure to clean your boat before and after each use in lakes and clean your waders, boots, and anything that has been in the water to prevent the spread of these. Link to aquatic invasives and boat cleaning rules and regs IDFG. There are many boating and fishing recreational opportunities on the Sawtooth NRA just make sure to follow regulations listed on the websites and get a fishing license and boating permits.
Mountain Pine Beetle – The mountain pine beetle (MPB) infestation and subsequent tree mortality started to increase in the late 1990’s and peaked around 2002 and 2003. Since that time, over 3 million lodgepole pine trees have been killed on the Sawtooth NRA. Since MPB prefer to attack and kill the larger diameter lodgepole pine, there is no longer enough susceptible host material to sustain their populations. As a result, we are seeing a decline in tree mortality as the infestation is starting to subside to endemic levels. In short, the infestation has run its course in the Sawtooth Valley where there are plenty of dead trees. The beetles are still somewhat active west of Stanley and we are seeing increased numbers of red and dead trees in the Wood River Valley. Of particular concern is the whiteback pine mortality on the higher elevations (i.e. Galena Summit). Whitebark pine is a critical high elevation tree that holds snow pack for watershed and is an important tree for wildlife.
Mountain pine beetles, like fire, are one of the natural disturbances that play a key role in regenerating lodgepole pine forests. These natural disturbances are native to our western landscapes and enable the short-lived, sun loving lodgepole pine to regenerate by making room for new trees to grow. Plans for bark beetle protection projects include applying preventive sprays and pheromones in high risk developed recreation sites to protect high value trees. Removing green infested and hazard trees will also be implemented as needed.
Douglas-fir Beetle – We have seen an increase in the numbers of beetle-killed Douglas-fir trees. They prefer to attack large, old trees in dense stands with a Douglas-fir component. Douglas-fir grow on the north and north-east slopes and it is common to find groups or stringers of dead and dying trees on the landscape. Mortality among the Salmon River is common below Stanley and near the Sunbeam area. Protection measures are being implemented on the Bald Mountain ski area by stapling pheromones to protect high risk trees.
Western Spruce Budworm – This is the most common and widespread insect that defoliates Douglas-fir and true firs. Larvae feed on new buds and needles late spring and early summer, causing a red halo appearance. It usually does not cause mortality but can stress the trees and make them more vulnerable to other insects such as the Douglas-fir bark beetle. Trees in the understory are more vulnerable to damage as larvae from the larger trees drop down on silken webs and land on the smaller trees.
Dwarf Mistletoe – Dwarf Mistletoes are natural parasitic plants that grow on branches and trunks of cone-bearing trees. The trees slowly weaken and can eventually succumb to a slow death. The easiest way to see if a tree is infected is to look for branch swellings or “witches brooms.
Mistletoes weaken trees by slowly robbing them of both water and nutrients in the infected areas. Infected trees start to die from the top down as more and more nutrients are taken by the infected branches below. The tree slowly dies until there are not enough live branches to sustain the tree. In our area, lodgepole pine and Douglas-fir trees are affected. Pruning infected branches can help to prolong the life of the tree.
Western Gall Rust – Western Gall Rust is caused by a fungus and is a common branch and stem disease found on lodgepole pine. It is an obligate parasite that requires living hosts for survival. It is easily recognized because of the oval round galls on branches and small stems. In the spring, they appear bright yellow to orange due to the fruiting spores. Over time, these points of infection girdle the trees and cause dead branches and even tree mortality – especially in young trees. Galls on main stems can last for decades and form “hip” cankers that may eventually kill the tree or, in most cases, result in stem failure from high winds. This can be a problem in our campgrounds and developed sites as the disease creates hazard trees.
Red-naped Sapsucker – Although not an insect or disease, this woodpecker creates “checkerboard” squares or sap wells in the bark of our younger lodgepole pine and aspen trees. They feed on the sap and on small insects that are attracted to the sap. The sap also attracts small rodents that gnaw at the damaged areas. Smaller trees and stems are sometimes killed due to the trees being girdled. The name “sapsucker” has been applied to the woodpecker genus Sphyrapicus because these birds create sap wells in the bark of woody plants and feed on the sap that appears here.