As a caver of some 25-years experience, I see bats in a different light. In my exposure to them, I've learned that instead of the blood-sucking, devious creatures of Gothic literature, they are in actuality incredibly beneficial. Bats are not rodents at all, and are more closely related to primates than mice or rats. If you examine a bat skeleton, their wings are very similar to our hands, with skin stretched between their finger bones, and thumbs extending from their wrists at the top of the wing.
Insects are the primary food source for approximately 70% of bat species. In North America, they consume an unbelievable number of insects that would otherwise feast on us (such as mosquitoes), or on our gardens and food crops. Some of their primary food sources are cucumber beetles, June bugs, stinkbugs, corn ear worms, tomato horn worms, cotton boll worms, coddling moths, and leaf hoppers, in addition to the larval root worms that are a primary pest for corn crops.  It is significant that they consume almost exclusively insects that are active at night without targeting beneficial insects or pollinators, which tend to be active during the daylight hours only.
Unfortunately, within the past five years, bat species in the United States began dying out in unprecedented numbers. A mysterious disease, dubbed White Nose Syndrome (WNS), caused by the fungus Pseudogynmnoascus destructans (originally called Geomyces destructans) was first identified in a cave near Albany, New York, in February of 2006, when a caver took pictures of bats with white furry patches on their faces and wings. It took about two years for a wide range of agencies (such as the New York State Department of Environmental Conservation, the New York State Department of Health, Cornell University and the U.S. Coast Guard) working simultaneously to isolate and identify the fungus.
Hallmarks of the disease are an odd white, fuzzy fungus that grows on the faces and wings of hibernating bats, and an inability to remain asleep throughout their hibernation period. Though the fungus is named for the distinctive fuzz on the muzzle of the bat, the impact on the bats' wings may be of more physiological concern. "G. destructans lives on bat skin, invading hair follicles and sebaceous glands, forming pockets on the surface of exposed wings, breaking through into the epithelium beneath. There it breaks down connective tissue and muscle and nerves into digestible nutrients. Under a microscope, researchers liken G. destructans mycelium to spaghetti wriggling into meat."  Damage to an organ that makes up such a large proportion of a bats' body is significant.
Normally, bats store up reserves of fat for the long winter, then slow their metabolisms and supress their immune systems during their long sleep. When infected with WNS, the bats awake frequently during the bleak winter months. It is unclear exactly what causes the bats to wake, whether it is irritation from the lesions on their wings, dehydration from electolyte loss from damage to their wings, or some other factor. The prematurely awakened bats' body temperatures must rise from the ambient cave temperature, often between 45-60 degrees Fahrenheit, to their active body temparature of around 100 degrees Fahrenheit. They emerge from their hibernacula and fly around, often even during the daytime, expending precious energy and depleting their fat reserves. Unable to either locate food or return to their hibernation state, the bats starve and freeze to death. The US Coast Guard estimates that the total population of bats in the northeast, where the syndrome began, has decreased by 80%.  Total losses from this winter have not yet been tallied, but will undoubtedly show continued mortalities.
Since 2006, white-nose syndrome has rapidly spread, and has impacted bats in at least 26 U.S. states and 4 Canadian provinces.  The origins of the invasive fungus in North America are unclear, though it is speculated that it was carried here by either a European bat on board a ship, or by someone who had visited a cave in Europe, then visited a cave in New York. The fungus is found in many European countries, though the bats there do not appear to be susceptible to it, and the widespread fatalities are not seen there. The fungus is thought to spread primarily from bat to bat, with migratory bats carrying the fungus to new areas each year. There is also the potential that human visitors to caves that have been infected with the Pseudogynmnoascus destructans fungus might unintentionally carry the spores to other caves on their shoes or caving gear.
Bats huddle close together during hibernation, which only increases the probability that the infection will spread quickly through a regional population. One of the reasons that bat colonies are unable to rebound from this disease is their relatively low birth rate. While many mammals bear litters of multiple young, bats generally have only one pup per year, and experience comparatively long lifespans of 12-20 years, depending on the species. Even bats that survive their first winter of exposure to WNS are unlikely to survive long-term, as the fungus continues to spread throughout the affected area.
Biologists are calling this "the most precipitous wildlife decline in the past century in North America."  Scientists estimate that some 5.7 million bats have died from the disease in a mere 5 years, with nearly 100% of the bats in exposed colonies succumbing to death as a result. "If it continues, scientists warn, WNS could result in the biggest decimation of a natural population since the extinction of the passenger pigeon. But while the passenger pigeon was only one avian species out of 10,000, collectively, bat species make up 25 percent of the world's total mammal types." 
As of February 2014, the disease has spread across much of the eastern seaboard, and is inexorably creeping westward, having reached as far west as Missouri, Iowa, and Minnesota, with suspected occurrences in Oklahoma. Refer to this map for specifics of what states have confirmed cases, and where suspected outbreaks have occurred.
The impact of this disease cannot be underestimated. "Somewhere between 20 and 25 percent of all mammalian species in the U.S. are bats, according to Hazel Barton of the University of Northern Kentucky in Highland Heights. The average bat eats 600 insects a night. With more than a million bat deaths last winter, 693 tons more insects buzzed and fluttered around the white-nose syndrome's range this summer, including moths that act as crop pests and mosquitoes that can carry West Nile Virus."  Several species of bats impacted by WNS are already listed as endangered in the United States; this includes the gray bat, the Virginia big-eared bat, the Indiana bat and the Ozarks big-eared bat. There are believed to be as few as 244,000 Indiana bats left in the wild. These bats are in danger of total extinction, if the advance of White Nose Syndrome is not halted.
Of practical concern to us all is the economic and environmental impact that the loss of our bat species might entail. Recent analysis estimates that the loss of hibernating bats through the combined effects of wind turbines and WNS could lead to agricultural losses of more than $3.7 billion/year.  "A joint research study between American and South African universities suggested that the bats that had died in the U.S. and Canada could have consumed approximately 8,000 tons (7,257 metric tons) of insects each year."  In addition to the increased cost of pesticides to offset the loss of this natural predator, we must consider the long-term impact that this drastic increase of pesticide use will have on other species, and the affect it will have on ground-water and other ecosystems. Significantly, if farmers are forced to use greater quantities of pesticides in the absence of the natural control the bats provided, the pesticides cannot be targeted to specific species of insects. Both harmful and beneficial insects, and especially pollinating insects which are already under stress and suffering from Colony Collapse Disorder, will be impacted.
The bottom line is this: our nation is experiencing a dramatic, devastating bat die-off of unprecedented seriousness, and the dire long-term environmental and economic impact can only be guessed. Simple principals of supply and demand tell us that as insect populations rise, the cost of controlling them will sky-rocket. Those costs will be passed on to consumers, in the form of elevated prices for all agriculturally based products, from produce in the grocery store, to processed foods containing corn, to higher costs for cotton clothing. As food crops become more expensive, so will the feed used for livestock, leading to increased costs at the meat counter. Though humans are not susceptible to White Nose Syndrome itself, we will all feel the impact of the loss it causes.
 Tuttle, Merlin. "Night Friends: Bats of the Americas" National Wildlife Federation, Bat Conservation International retrieved from pdf online activity guide,on Mar. 9, 2014
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Thumbnail image at start of article, Tricolored Bat with White Nose Fungus, Flickr Creative Commons, by photographer Pete Pattavina, submitted by US Fish and Wildlife Service (USFWS) Headquarters. Some rights reserved.
White Nose Syndrome on a Little Brown Bat, Flickr Creative Commons, by photographer Ryan von Linden, New York Department of Environmental Conservation, submitted by USFWS Headquarters. Some rights reserved.
Wing Damage on a Little Brown Bat from WNS, Flickr Creative Commons, by photographer Ryan von Linden, New York Department of Environmental Conservation, submitted by USFWS Headquarters. Some rights reserved.
Cluster of Indiana and Little Brown Bats, Flickr Creative Commons, by Tim Krynak, submitted by US Fish and Wildlife Service - Northeast Region. Some rights reserved.
Little Brown Bat with WNS, Flickr Creative Commons,by Jonathan Mays, Wildlife Biologist, Maine Department of Inland Fisheries and Wildlife, submitted by USFWS Headquarters. Some rights reserved.