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Do dragonflies mean safe drinking water?

dragonfly on window screenThe Question: Someone recently told our young son that if you see a dragonfly near water (such as a pond), then it is safe for humans to drink the water. Is this true?

Submitted by: Jean, Minnesota, USA

(click on photos and graphics to expand)

dragonfly by John FlanneryThe Short Answer:  Dragonflies are indictors of water quality, but that relates to the ecological health of a stream, or pond, or lake, not to its safety for people to drink.  Public health experts will tell you that you can’t assume any lake, pond, stream or river in the United States is safe to drink.  On the other hand, some hikers claim they drink water from high mountain streams all the time with no resulting illness.  You can never be sure about that, however.  That’s why most hikers either boil, chemically treat, or filter water before drinking.

Dragonflies can be found flying over water with an active infestation of Giardia, for example. Or salmonella. And virtually all water with animals in it will have E. coli and other bacteria. And if there are people swimming in the pond, that adds another potential source of disease-causing microorganisms. For most people with a healthy immune system, the bacteria and parasites floating around in your typical lake or pond won’t cause a problem. After all, we all get water in our mouths every time we swim in a lake, pond, or stream.

Deliberately drinking pond water, however, is probably pushing your luck.

dragonfly larva - Matt KeevilMore Information: Field ecology programs teach people to use a Biotic Index Card, as a relatively accurate method of assessing the overall level of ecological health or disruption of aquatic systems that a non-scientist can use with just a little training. The biotic index method is based on the fact that aquatic insects, both those that spend their entire lives in water, and those whose larval stages take place in water, have differing levels of sensitivity to pollution and disruption. For example, mayflies (Ephemeroptera), are rarely found in polluted or disturbed water. They need fairly pristine conditions or they won’t thrive. Flies (Diptera) that have aquatic larvae, on the other hand, are generally tolerant of dirty, polluted water. So if you find mayflies, that’s a good sign that the body of water is relatively healthy. If all you find are fly larvae, that’s a bad sign.

Dragonflies and Damselflies (Odonata) fall somewhere in between. They’ll grow in super clean water, but they’ll also do okay in water that isn’t quite perfect. They generally won’t grow in badly polluted water, however. That’s why there’s some truth to the statement about dragonflies and clean water. If you have dragonfly larvae in the pond or lake, it can be taken as a rough indicator that the body of water is not badly polluted.

Note, however, that this has little to do with whether the water is safe for humans to drink. For people, in addition to worrying about chemical pollution, you also have to worry about disease-causing microorganisms.

Also, the Biotic Index Card is an overall guide. There are several hundred species of dragonflies in North America and some are more fussy about water quality than others.

A study in Rhode Island categorized hundreds of bodies of water as to the level of pollution and disruption. The researchers then matched up adult dragonflies with bodies of water and noted whether they were found in disturbed bodies of water or not. They created a score from 0-10, where 0 means the dragonfly species is only found at badly disturbed and polluted bodies of water, and 10 means the species is only found at bodies of water that are very clean and undisturbed. So 10 means very fussy about water quality, and zero means not at all fussy.

damselfly by Charles J SharpFor the 135 species of dragonflies found in Rhode Island, the average score of all species was 6.4, suggesting that adult dragonflies are indeed somewhat fussy. They are mostly associated with less disturbed bodies of water. But the scores range from 10 for half a dozen species (such as Dorocordulia libera) that were only ever found in bodies of water characterized as “least disturbed,” all the way down to a score of 0 for the damselfly Ischnura ramburii, which was found only in the “most disturbed” bodies of water.

So unless you know your dragonfly species and their exact correlation with clean water, the presence of adult dragonflies over a body of water would give only the roughest of gauges. Certainly not anything I’d recommend as a guide to the safety of drinking.

Sources: Kutcher, T E, Bried, J T., 2014, Adult Odonata conservatism as an indicator of freshwater wetland condition. Ecological Indicators. 38:31-39.

Zimmerman, M. C. 1993. The use of the biotic index as an indication of water quality. Pages 85-98, in Tested studies for laboratory teaching, Volume 5. Proceedings of the 5th Workshop/Conference of the Association for Biology Laboratory Education (ABLE), 115 pages. Viewed on 7/8/2016 at http://www.ableweb.org/volumes/vol-5/6-zimmerman.pdf.

William E. Sharpe, William G. Kimmel, and Anthony R. Buda. Biotic Index Card. Viewed on 7/8/2016 at http://www.pspb.org/water/media/BioticIndexCard.pdf.

Cite this article as: Pelletier, TC. (July 11, 2016). Do dragonflies mean safe drinking water? Retrieved from http://askanaturalist.com/do-dragonflies-mean-safe-drinking-water/ on July 24, 2016.

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What are these bubbles all over the lake?

bubbles on a lakeThe Question: In early June, I took a kayak trip on Winton Lake, starting out before sunrise and getting to the area where these photos were taken just as the sun was coming up. There were green bubbles all over the lake. After the sun came up, they began to break up and were gone within about an hour after sunrise. I’ve never seen anything like this on any lake I’ve ever paddled and I’m very curious what could cause it! Can you supply any answers?
Submitted by: Mark, Ohio, USA

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The Short Answer: Mark, I think I can give you a general answer, but a specific answer would require some investigation at the site. What you saw is probably a cyanobacterial slime or mat that has trapped bubbles of gas, produced by the cyanobacteria. The bubbles might be oxygen, carbon dioxide, or some mixture of the two. Cyanobacteria often dominate in waters that are over-enriched with nutrients. Mark June-Wells, a certified lake manager, and founder of Aquatic Ecosystem Research, in Connecticut, has not seen this bubble phenomenon before, but he suggested “That is most likely cyanobacteria that are at the surface in the early morning.  The reason they are bubbling is likely due to their density and their metabolic byproduct (oxygen) which forms the bubbles.  An alternative hypothesis is that the bubbling is due to respiration, which yields carbon dioxide. The algae may be modifying their buoyancy to optimize light harvesting.”

bubbles on a lakeMore Information: Cyanobacteria used to be called “blue-green algae.” They aren’t really what we usually think of as algae, however. They are actually bacteria and exist in virtually every body of surface water in the world. About three billion years ago, they evolved the kind of photosynthesis that releases oxygen. The cyanobacterial cells capture sunlight as a source of energy to split carbon dioxide (CO2) into carbon and O2. The carbon is used to build organic compounds, leaving the O2 free to join the atmosphere as free oxygen. In today’s world, most oxygen is produced by true algae and other plants, but cyanobacteria probably created the oxygen-rich atmosphere that allows oxygen-loving creatures like us to exist. So although cyanobacteria have gotten a bad name these days – for good reason – we should probably also remember that we owe them for every breath we take.

Cyanobacteria have gotten a bad name because many species release multiple toxins that can kill fish, birds and other organisms. According to the World Health Organization, “The only documented and scientifically substantiated human deaths due to cyanobacterial toxins have been due to exposure during dialysis.” Of course, in the very next sentence, WHO says, “People exposed through drinking-water and recreational-water have required intensive hospital care,” so cyanotoxin poisoning can be a pretty severe thing.

We don’t yet know exactly why cyanobacteria are sometimes, but not always, toxic, but it doesn’t seem likely that the cyanobacteria are “trying” to poison us. Recent research suggests the toxins help protect cyanobacteria from reactive and destructive forms of oxygen such as superoxide and hydrogen peroxide, which are often produced in warm summertime surface waters. The toxins may also be effective against tiny zooplankton grazers like daphnia, rotifers, and copepods and reduce parasitism by certain types of fungus. Toxins are probably the weapons the cyanobacteria use to protect themselves from all these dangers.

In aquatic ecosystems with normal levels of phosphorus, cyanobacteria never become numerous enough for their toxins to affect vertebrates. But lakes, ponds, rivers, and ocean bays that have been over-fertilized by agricultural and lawn runoff, or by nitrogen and phosphorus released from sewage systems, can provide a habitat where cyanobacteria “bloom,” multiplying far beyond the ability of grazers and parasites to keep them in check.

And in some highly fertilized waters, cyanobacteria slime or mats form on the surface or on the bottom. Dr. Hans Paerl, Kenan Professor of Marine and Environmental Sciences, who studies cyanobacteria at the University of North Carolina Institute of Marine Sciences, thinks that’s what is going on here. “Fascinating shots!  It looks like an algal bloom, most probably cyanobacterial, that may have started on the lake bottom (as mats) and then made its way to the surface due to oxygen bubbles (formed by algal photosynthesis) that gave the mat some buoyancy and made it float. I can’t be sure what the organisms are, but cyanobacteria in the genera Nostoc, Lyngbya and Oscillatoria are known to form floating mats that often start on the lake bottom.”

If You See This Phenomenon: As questioner Mark noted, this phenomenon was very brief and the bubbles disappeared once the sun came up. Probably the warmth of the sun on the bubbles expanded the gas inside and they popped. Or Dr. Paerl suggests the gasses were reabsorbed, causing the cyanobacteria mat to lose buoyancy and sink again. Neither of the experts I contacted had actually seen this particular phenomenon themselves, and in my own search of the internet I was only able to find one other example, a photo taken of an irrigation pond in California’s wine growing region by George Rose (http://www.gettyimages.com/license/458453830), so if anyone else observes these green bubbles on a lake and can take a picture, I’d love to see it. Email them to tom@askanaturalist.com.

Sources: Paerl H W, Gardner W S, Havens K E, Joyner A R, McCarthy M J, Newell S E, Qin B, Scott J T. 2016. Mitigating cyanobacterial harmful algal blooms in aquatic ecosystems impacted by climate change and anthropogenic nutrients. Harmful Algae 54. 213–222.

Paerl, H. W., & Otten, T. G. (2013). Blooms bite the hand that feeds them. Science, 342(6157), 433-434.

Rohrlacka T, Christiansenb G, Kurmayerb R. 2013. Putative Antiparasite Defensive System Involving Ribosomal and Nonribosomal Oligopeptides in Cyanobacteria of the Genus Planktothrix. Applied and Environmental Microbiology. Vol. 79 no. 8. 2642-2647.

Wilson A E, Sarnelle O, Tillmanns A R. 2006. Effects of cyanobacterial toxicity and morphology on the population growth of freshwater zooplankton: Meta-analyses of laboratory experiments. Limnology and Oceanography., 51(4), 1915–1924.

Water-related diseases: Cyanobacterial Toxins. Prepared for World Water Day 2001. Reviewed by staff and experts at the Federal Environmental Agency, Germany, and the Water, Sanitation and Health Unit (WSH), World Health Organization (WHO), Geneva. Viewed on June 27, 2016 at: http://www.who.int/water_sanitation_health/diseases/cyanobacteria/en/.

Cite this article as: Pelletier, TC. (June 29, 2016). What are these bubbles all over the lake? Retrieved from http://askanaturalist.com/what-are-these-bubbles-all-over-the-lake/ on July 24, 2016.

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What is this long, skinny insect?

walking stick -2 - 800The Question: I found this on my driveway. It doesn’t look like anything I’ve ever seen. It was about 7.5 cm (3 in.) long. What is it?

walking stick - 800Submitted by: Debbie, Manitoba, Canada

(click on photos and graphics to expand)

The Short Answer: Debbie, this is a water scorpion, almost certainly the brown water scorpion (Ranatra fusca) because that is the only Ranatra species common in Manitoba. Water scorpions are not scorpions at all, but are actually aquatic insects, members of the order Hemiptera, the “true bugs.” Brown water scorpions are the most common water scorpions in North America and can be found across a wide area of the continent. Despite the name, they can vary quite a bit in color. They look something like walking stick insects, but water scorpions aren’t closely related to walking sticks, which are members of a different order entirely, the Phasmatodea.

More Information:  Water scorpions are found in fresh water on all continents except for Antarctica.  One of your excellent photos captures the wings of the water scorpion.  These insects lay their eggs under water, and complete all their development under water.  But they may fly to disperse from their natal ponds.

At the tail end, water scorpions have two projections that come together to form a breathing tube that the insect can extend above the surface of the water.  It’s this extension that reminded people of a scorpion, and earned it the descriptive name, but water scorpions don’t have the ability to inject venom with their “tail” the way scorpions do.

In fact, if there is trouble, it’s at the other end of the creature.  The modified front legs of a water scorpion are used to grab and capture prey, in much the same way that a praying mantis uses front legs to grasp prey.  And it’s also at the front end that the water scorpion has a piercing mouth tube that injects venom into its prey.  This venom includes paralyzing agents as well as enzymes that digest the prey’s insides, which the water scorpion then sucks out.  Though there’s far too little venom to paralyze you nor allow a water scorpion to suck your insides out, the venom it injects can be painful if it gets under your skin, so it’s best to handle water scorpions carefully.

Water scorpions are “ambush predators.”  They attach themselves to underwater plants and wait for suitable prey to swim by.  That prey can be other aquatic insects or crustaceans, small tadpoles and fish … pretty much anything it can grab and subdue.  They are voracious predators of mosquito and black fly larvae, so I hope you treated your visitor well and thanked it for all its hard work to reduce the number of bloodsuckers in your backyard.

If you watch this video, you’ll see a water scorpion capturing daphnia, tiny aquatic crustaceans. At about the one minute mark, you’ll see that this water scorpion catches a second daphnia before it has even finished feeding on the first one it catches.

https://www.youtube.com/watch?v=yiBgQj-Rd20

400px-Nepa_rubra2 - Holger GröschlTwo Types of Water Scorpions: The water scorpion you found is from the subfamily Ranatrinae. The species in that group are all thin and stick-like. The other subfamily of water scorpions, the Nepinae, has a flattened, beetle-like body as shown in this photo of a species in the genus Nepa. Despite the difference in shape, the habits and hunting methods of the two groups are fairly similar.

Sources: Sites, R and Polhemus J T. (1994). Nepidae (Hemiptera) of the United States and Canada. ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 87, no. 1.

Thanks to Bugguide.net.

Cite this article as: Pelletier, TC. (June 25, 2016). What is this long, skinny insect? Retrieved from http://askanaturalist.com/what-is-this-long-skinny-insect/ on July 24, 2016.

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Osprey struggling to get off the water

This is beautiful slow-motion footage from the BBC of an osprey trying to lift off with a heavy fish.  Unfortunately, the narration repeats an old myth that an osprey’s talons lock and can’t be released and therefore a strong and heavy fish can pull an osprey underwater and drown it.

Osprey can definitely release fish in the water or in air after grasping it. They sometimes simply lose their grip on a struggling fish as they fly. Eagles often wait for an osprey to catch a fish and then try to steal it. When that happens, the osprey sometimes decides to drop the fish and let the eagle have it, rather than engage in a mid-air battle with a much bigger eagle. Osprey also sometimes drop fish into their nest before landing. So they aren’t getting irreversibly locked onto fish as a general rule. What makes sense is that if an osprey buries a talon or two too deeply, it might get stuck in the flesh of the fish and be hard to remove, almost like a fish hook. And if the fish is big enough to pull the bird underwater, osprey aren’t built for swimming, so it might very well drown before it can get free.

So I’m not disputing that an osprey can be pulled underwater or drown. But ignore that myth about irreversibly locking talons, and just enjoy the beauty of the osprey’s wings.  Amazing!

HIghlands – Scotland’s Wild Heart: Osprey slow-motion footageThis osprey’s having a bit of bother with its fish supper…

Ewan McGregor narrates this dramatic super slow-motion footage in a wee sneak peek at #Highlands

Posted by BBC Scotland on Monday, May 9, 2016

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Why did these coyotes attack?

California Death Valley Coyote)The Question: Why did coyotes attack me and my dogs?

Submitted by: Jessie, Arizona, USA

(click on photos and graphics to expand)

The Longer Question from Jessie: “I live in central Arizona, and was out walking my three dogs on a rarely used trail at approximately 8:30 a.m. Part of the trail passed by a pool of water, which is rare in the area I was hiking in. As I was passing, a coyote appeared about 30 feet away and started vocalizing and making itself as visual as possible. I stopped for a few seconds, expecting it to run away as has happened with every other encounter I’ve had with a coyote.

“Instead, approximately eight other coyotes silently circled in and tried to attack us. They were lunging within four to five feet of my dogs and I. My dogs were terrified and just froze, so there was no aggression on their part. I started yelling and throwing rocks at the coyotes, but they had no fear. I am on the short side and only weigh 70 lbs, so that may have been a contributing factor.

“We somehow broke out of the circle, but they continued to follow us for about ten minutes. Two or three would emerge from the junipers, backs hunched and vocalizing while the rest of the pack positioned themselves to emerge somewhere ahead of us on the trail. They were quite brilliant in their strategies.

Coyote_arizona“Is this typical coyote pack behavior? Is it strange to have such a large pack? Were they trying to hunt us or were they just protecting a rare source of water in the middle of the desert? I’ve only ever seen coyotes as lone individuals, or in pairs, and they’ve always been timid.”

The Answer: Jessie’s description of facing these coyotes (Canis latrans) sounds terrifying, and I’m glad she kept her head under these condition. I asked Paul R. Krausman, a Certified Wildlife Biologist at the University of Montana, who studies coyote behavior and human and coyote interactions, for his thoughts on this situation. Here’s what he said:

“What Jessie describes is an interesting situation, and one that could have been troublesome. It is unlikely they were protecting the water. Predators will use water when available, but are adept at obtaining moisture from their prey.

“The large pack could have been a female and her pups with one or two others and their intent was likely to attack the prey (the dogs). The owner’s attempt to discourage the coyotes by tossing rocks may have been more of a deterrent than she knew. Coyotes do hunt in packs and do hunt as described. It is very effective as the prey can’t watch all of them at once and if one can blindside the prey, they have been successful.”

Robert Timm, retired director of University of California Hopland Research & Extension Center and a UC Cooperative Extension wildlife specialist, told me, “There are increasing numbers of reports of coyotes confronting or attacking people and pets (including at times dogs on leashes) from many areas throughout North America.  The experience of your reader is not atypical of what’s reported, particularly in areas where coyotes are now sufficiently habituated to humans to be living essentially full-time in suburbia or in natural areas frequented by tourists (e.g., state and national parks, campgrounds, hiking trails,) where coyotes likely come into contact with humans who have food… and probably intentionally feed coyotes in many instances, thereby increasing and speeding up the habituation process.  The reader didn’t mention the size or breed of the dogs involved; for medium to large dogs, such confrontations may be territorial defense, but for small to medium dogs I suspect the coyotes often regard the dogs (as at times they do toddlers and small children) as potential prey.”

Coyote pupDavid L. Bergman, Arizona State Director, USDA APHIS Wildlife Services, gave what seems like a reasonable explanation of what happened. “Based on the information provided I would consider that the coyotes were being territorial and protecting a den.  The owner’s dogs i.e., other canines, would be considered a threat to any new born pups in the den and thus a target for the territorial pack animals.  In Arizona, coyotes usually breed in February or March and have’a gestation period of 63 days. Birth of the pups could be during April or May right around when the individual had the encounter.  As to the pack size, it is likely that the pack was made up of the dominant male and female and last year’s pups that had not dispersed.  Pups disperse anywhere from 4 to 10 months of age with some dispersing after 1 year of age. As to the behavior of the attack, size will not matter when they are protecting pups.  From what is described, the coyotes showed their hand in that they were willing to protect their den site and they worked together to herd the intruders out of the area.”

The Experts’ Warning: All of the experts I consulted expressed the same concern that coyotes habituated to people can be dangerous, especially to pets and children. A paper co-authored by Robert Timm outlined a “sequence of increasingly bold coyote behaviors” by coyotes:

Nighttime coyote attacks on pets … sightings of coyotes in neighborhoods at night … sightings of coyotes in morning and evening … attacks on pets during daylight hours … attacks on pets on leashes and chasing of joggers and bicyclists … and finally, mid-day sightings of coyotes in and around children’s play areas. (From Timm et al 2004).

I tend toward tolerance and acceptance of wildlife, rather than aggression, but the experts agree that with coyotes this is a mistake. Human-coyote interactions have become more common across North America and attacks on pets and even people have grown sharply since the early 1970s. I believe our modern tendency to be friendly to wildlife is generally a good thing, but when applied to coyotes, it may be asking for trouble, putting people and pets at risk and leading ultimately to lethal control of coyotes when they cause problems. It’s not easy to re-instill a fear of humans in coyotes that have become habituated, so it’s better to keep them nervous from the start.

Coyotes start out wary of people, and the experts generally recommend yelling at them, throwing rocks at them, and otherwise harassing them to keep them wary. Don’t leave pet food outside, and take special care with children and small pets in areas where coyotes have been seen. Never feed coyotes.

Standing up to Aggressive Coyotes: The University of California has an excellent summary of information about human and coyote interactions. In it they suggest a strategy for standing up to a coyote. “If you or your pets are approached by an aggressive or fearless coyote, try to frighten it away by shouting in a deep voice, waving your arms, throwing objects at the animal, and looking it directly in the eyes. Stand up if you are seated. If you are wearing a coat or vest, spread it open like a cape so that you appear larger. Retreat from the situation by walking slowly backward so that you do not turn your back on the coyote.”

Given these suggestions, it sounds like Jessie did the right thing.

Sources:

Timm, R.T, Baker, R.O., Bennett, J.R., Coolahan, C.C. (2004). Coyote Attacks: An Increasing Suburban Problem. Proceedings of the Twenty-First Vertebrate Pest Conference (2004) (R.M. Timm and W.P. Gorenzel, Eds.), 47-57.  http://escholarship.org/uc/item/8qg662fb

Alexander, S.M. & Quinn, M. S. (2008) Human-coyote (Canis latrans) interaction in Canadian urban parks and green space: Preliminary findings from a media-content analysis. Contributed paper for the Canadian Parks for Tomorrow: 40th Anniversary Conference, May 8 to 11, 2008, University of Calgary, Calgary, AB.

Coyote. (03/2007) Retreived from http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74135.html on 5/10/2016.

Photo Credits:

1. Manfred Werner (Tsui [de.wikipedia]) – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=41179

2. marya (emdot) from San Luis Obispo, USA (Flickr) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

3. By g’pa bill – “Mom, I’m Bored”…, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=22832514

Cite this article as: Pelletier, TC. (May 12, 2016). Why did these coyotes attack? Retrieved from http://askanaturalist.com/why-did-these-coyotes-attack/ on July 24, 2016.
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