The Short Answer: I’m answering this question a tad late, in mid-April, so most of the snow in the U.S. is gone, but as deep snow melts, it often melts first around the base of trees, as Raymond mentions. Notice that a snow ring shows in this photo of a flower pot. This is a clue that it’s probably not that the trees are generating heat biologically, although some plants are capable of doing that. What happens with trees is that the tree branches keep some snow from reaching the ground. Suspended in the branches, that snow is subjected to more sun than snow distributed on the ground so it melts and never falls all the way to the ground under the tree. Also, when the sun is shining, the tree absorbs more heat than the surrounding snow. This happens because the tree is darkly colored — especially after the snow has melted so that the dark branches or evergreen needles are exposed. The tree trunk gets warm, and then radiates some of that heat back out, which melts the snow around the base. The same thing happens with the flower pot and other objects like telephone poles and fence posts.
More Information: This phenomenon occurs under deciduous trees that have dropped their leaves, and even more under evergreens because they catch more snow, and the dark color of their needles helps them absorb more heat, compared to deciduous trees, which are generally lighter colored. In fact, in northern evergreen forests that get large amounts of snow, the “snow wells” around trees can be two meters (6 feet) deep or more. This represents a serious danger to hikers and skiers who sometimes fall into the wells and can’t get back out.
This website gives information on the dangers of snow wells and tips for escape: http://www.deepsnowsafety.org/index.php/
Snow well paradox: Scientists study snow wells because the phenomenon that creates them has a significant effect on how heat and water are absorbed in northern forests. In their studies, they’ve found something surprising. Though the warmth radiating from the tree often melts the snow around the trunk, that same area also experiences the deepest frost. How does that happen? The bare ground at the base of the tree is exposed to the frigid winter air, especially at night or in cloudy weather when the sun is not warming the tree. The surrounding areas, covered by snow that is often quite deep, are insulated from the worst of the cold. Though the snow melts around the tree, paradoxically, that’s also where the frost goes deepest.
|The Question: I noticed this little frog stuck to the outside of my exterior door about 11 p.m. The porch light was on and was attracting various “bugs” which I assume the frog was taking a keen interest in. I saw the frog jump from the door to this position next to the bug, which I assume looked like dinner? Anyway, what kind of frog and bug is this?
Submitted by: Chris, Cobb County, GA
The Short Answer: This is a green tree frog (Hyla cinerea) and the beetle is a pine sawyer beetle in the genus Monochamus, probably the Carolina pine sawyer (Monochamus carolinensis – thanks to the people at BugGuide.net for the ID). Both the Carolina pine sawyer and the green tree frog are common throughout the southeastern United States, so seeing these two together is not surprising.
Insect predators like the green tree frog often cleverly hang out where outdoor lights attract insects. That’s probably what this one was doing. It seems like this beetle might be a bit on the large side for this frog, but maybe not. One study showed that the green tree frog, like many other frogs, responds most to movement. So as long as this beetle stays perfectly still …
Destructive Invasive Species: The Carolina pine sawyer is one of more than 20,000 species of “long horned” beetles in the family Cerambycidae, so called because their antennae are often longer than their bodies. Many of the long horned beetles feed on trees, either living or dead. In the United States, the most well known long-horned beetle at present is probably the Asian long-horned beetle (Anoplophora glabripennis), which is considered to be a major –possibly catastrophic – threat to trees all over the country. Conservation and environmental authorities are conducting aggressive control programs to limit the spread of this non-native invasive beetle. For more information from the USDA, click here, and report any sightings of long-horned beetles by clicking here.
If you read about the Asian long-horned beetle and live in North America, you probably fear for your trees, and you might curse the processes that bring so many invasive animals and plants to our shores. But remember that the process goes in both directions. In Japan, for example, they curse the arrival on their shores of our pinewood nematode, a tiny worm with a very close connection to North American pine sawyer beetles.
The Beetle-Nematode Connection: Adult Carolina pine sawyers carry tens of thousands of the pinewood worms also known as the pine wilt nematode (Bursaphelenchus xylophilus). Nematodes in the Bursaphelenchus genus feed on fungi that grow on dying or dead trees. The worms are not particularly mobile, but they hitch a ride from dead tree to dead tree on insects like the Carolina pine sawyer. The pine wilt nematode has developed a further ability that others of its genus don’t seem to have, which is that it is able to grow and multiply in some live, healthy trees. More on that in a minute.
In North America, to which the Carolina pine sawyer and the nematode are native, the adult beetles feed on the branches of live trees. The beetles don’t seem to do any serious damage to a healthy tree and importantly, the pine wilt nematodes they carry don’t seem to do much damage. After feeding on live trees for about two weeks, the adult female beetles then find a dead or dying tree, cut a hole through the bark and lay their eggs. As they do so, the nematode worms jump ship (okay, crawl ship) and enter the tree through the hole made by the female beetle. Once in the tree, the worms multiply. Meanwhile, the beetle egg has hatched and is likewise eating the decaying tree tissue. When the beetle larvae reaches full size and metamorphoses into an adult beetle, the nematode worms crawl aboard the new adult beetle before it chews its way out of the tree and flies away. The adult beetle finds another dead or dying tree in which to lay its eggs, and the cycle begins again.
Notice, however, that the beetle and nematode don’t do much harm to healthy trees. And this is the story in North America for our native pines. However, the pine sawyers and their nematode friends can do great damage to non-native decorative pines like Austrian pines, Scotch pines and Japanese pines. When a pine sawyer beetle feeds on healthy trees of these species, it transmits the nematodes, which then multiply rapidly in the tree and can kill a tree in just weeks.
This is exactly what the pine wilt nematodes have been doing to pine trees in Japan since early in the 20th Century. It’s likely that that the nematodes reached Japan in trees imported from North America. Once there, it was spread by Monochamus alternatus, the Japanese pine sawyer, which previously had not been infected with the pine wilt nematode. The nematode is now a major problem in Japan, Korea, China and Taiwan and may now have gained a European foothold in Portugal.
To see a diagram of the life cycle of a Monochamus beetle and the pine wilt nematode, click here (about half way down the page).
In this country, we fear the potential for disaster that could be caused by the Asian long-horned beetle, but our own pine wilt disease – spread by Monochamus beetles– long ago became an ongoing ecological disaster in Asia, causing the deaths of uncounted millions of trees.
What Protects North American Trees: The situation in Asia is perfect for the beetles and nematode worms. The adult beetles feed on healthy trees, introducing the nematodes, which kill the tree, making it available for use by the beetle larvae, which then carry the nematodes to the next healthy tree. North American trees have developed some resistance to this process so that the nematodes only become established in trees that have been killed or seriously weakened by some other disease, insect damage or damage.
Special Thanks to Michelle Cram, biologist for the U.S. Forest Service in Atlanta, Georgia, USA, for her assistance and her correction of errors in the original version of this article.
Akbulut, S, & Stamps, W T. (2012). Insect vectors of the pinewood nematode: A review of the biology and ecology of monochamus species. Forest pathology, 42(2), 89-99.
Kikuchi, T, Cotton, J A, Dalzell, J, et al. (2011). Genomic insights into the origin of parasitism in the emerging plant pathogen bursaphelenchus xylophilus. PLOS pathogens, 7(9).
Freed, A N. (1980). Prey selection and feeding behavior of the green treefrog (hyla cinerea). Ecology, 61(3), 461-465.
How to Identify and Manage Pine Wilt Disease and Treat Wood Products Infested by the Pinewood Nematodes http://www.na.fs.fed.us/spfo/pubs/howtos/ht_pinewilt/pinewilt.htm – 10/8/2012.
An Overview of the Pine Wood Nematode Ban in North America –
http://www.forestpests.org/pinenematode/ – 10/7/2012.
|The Question: About 70 tadpoles showed up in my pond. I don’t mind a few, because I like frogs, but what can I do with the rest of them?
Submitted by: Joanna, UK
The Dialogue: (For something a little different from the usual format of my posts, I will share the emails that went back and forth on this question.)
Tom: Hi Joanna. Thanks for your question. This is in a garden pond, I assume? Any idea what kind of amphibian tadpoles they are?
Joanna: Hi tom. Yes, this is my garden pond. Here’s a picture. I have no idea what kind of tadpoles. I just don’t know what to do with them all. I am at the moment trying to clean my pond out and have managed to put about 15-20 of the tadpoles in a bucket. Will they be okay? What about the rest that are still in the pond? When the pond drains out will they die?
Tom: Until they turn into frogs or toads or salamanders or whatever they are, they will need water, I’m afraid. And water with food in it. For some species, that means algae, for others insects. Are you refilling the pond immediately? If so, I’d suggest keeping the tadpoles in a bucket and put them back once you refill the water. If not, then you might want to move them to a nearby lake or pond. Whatever nearby habitat seems most like your pond.
Joanna: I will be refilling the pond straight away. How have they survived this long without food? Will I have to go out and buy food for them? There are some leaves in the bucket from the pond. Is that okay? And some small insects floating on the top of the water. Is that a bad thing?
Tom: They are probably finding the food they need in your pond. If the pond has been there for any length of time, I’m sure you have algae and microorganisms and insects and things like that. The parents who laid the eggs in your pond probably have a way of judging it as a food supply. Leaves in the bucket is good. They undoubtedly contribute to the stuff the tadpoles were eating. For example, decaying leaves are food for microorganisms that the tadpoles might be eating.
You said you were cleaning the pond. Are you cleaning out all the leaves and gunk? If so, that might remove a good part of the food supply for the tadpoles, but I’d just put the tadpoles back and hopefully, they’ll do okay. Don’t forget, with animals like amphibians that lay hundreds of eggs, only a very small percentage ever survive anyway. So even if you left the tadpoles there, only a handful of your 70 were going to survive anyway. That’s just the way it works.
Joanna: Thank you again, Tom. I won’t empty the pond completely, just enough so the water can be cleaner to the eye. I will let you know how I get on at a later date. I will leave some of the leaves in the pond too, and I have a water lily in there for them so food should be on that too.
Tom: That’s very considerate of you towards the tadpoles. By the way, do you have chlorine in your water? Most municipal water systems do. If so, that might cause a problem with the tadpoles when you refill the pond. Here in the U.S., pet stores sell chlorine neutralizer products for tap water for ponds. I think you’re already doing more than most people would do to care for the tadpoles, but if you have the chance to neutralize any chlorine, that would help them, too.
Joanna: Tomorrow, I will get some neutralizer from the pet shop which isn’t far from my home. I don’t mind doing this. As a child I always loved frogs/toads. My favourite book as a child was The Princess and the Frog, so if I can save at least one or more, I will be happy and I will have my frog!
Tom: Well, I’ll keep my fingers crossed for you, but we don’t know that these are frog tadpoles. How would you feel about The Princess and the Toad? Or The Princess and the Salamander? By the way, your pond is beautiful!
Joanna: I really do think that what I have are either frogs or toads. I wouldn’t want them to be salamanders. I hadn’t heard of them, so I looked them up and they look a bit scary to me.
Tom: One of the nice things about doing this website is that I keep learning things I didn’t know. For example, I was unaware that England had so few salamanders. In fact, some people would say that England has no salamanders. What it does have is three species of newts. Personally, I consider newts to be salamanders, and they are in the family Salamandridae, but they are in their own subfamily, the Pleurodelinae, so taxonomically, they are somewhat distinct. England has relatively few species of native amphibians, presumably because after the last ice age, England was fairly quickly separated from the rest of Europe by the English Channel and therefore cut off from the surviving populations of amphibians that recolonized most of Europe.
If you get a chance to take a picture of your tadpoles, send it in. You can tell newt tadpoles from frog or toad tadpoles in England because newt tadpoles have visible external gills, as you’ll see in this photo. Also, newt tadpoles develop their front legs before their hind legs. Frog and toad tadpoles develop back legs first. The most likely frog found in garden ponds in England is the aptly named common frog (Rana temporaria). The other, less likely, possibility is the also aptly named common toad (Bufo bufo), but they prefer deeper waters for breeding, and their tadpoles are less commonly found in garden ponds, so unless your tadpoles have gills, it’s most likely you’ll get your frogs.
By the way, for the most part, salamanders and newts shouldn’t worry you. They are generally small, slow moving, harmless creatures. There are a few large salamander species that live in big rivers, but not in England.
|The Question: While walking along a busy section of Boston Harbor the other day, I noticed hundreds of jellyfish floating on the surface. I walked about a half mile stretch of water, and they were everywhere. They all seemed to be the same kind – translucent white, with four circular bits in the center of their bodies. There were all different sizes, too. It was an extremely sunny and warm day, which I first thought might be the reason, but the next couple have been cool and rainy, and they are still on the surface! Any ideas?
Submitted by: Marion, Boston, Massachusetts, USA
The Short Answer: What you saw are floating medusae of the moon jelly (Aurelia aurita), one of the most common jellyfish in the world. They like protected waterways, and are tolerant of the wide range of salinity and temperature that you often find in harbors and bays. They also become larger and more visible in the summer, so they are a common sight in city harbors around the globe.
Many species of jellyfish, including moon jellies, have increased in the last decade. Factors that probably favor moon jellies and other species include manmade objects in the water, warmer temperatures, overfishing, and fertilizer runoff. Here’s a video from Boston Harbor in summer 2010 that shows the jellyfish:
More Information: Here’s how the four factors mentioned above favor jellyfish:
- Manmade objects in seawater – most jellyfish, including moon jellies, have a polyp stage that attaches to a hard object such as a rock. Polyps generally can’t settle on shifting sand, or organic sediment. By building structures into the water, such as piers and docks, and by allowing plastic and other manmade trash to be washed into our harbors and bays, we provide lots of hard surfaces for jellyfish polyps.
- Warmer water due to climate change – moon jellies develop faster in warmer water, so increases in temperature due to climate change shorten the time between generations. In addition, the cold water of winter usually kills the swimming moon jellies, leaving only the attached polyps to start the next generation. With warmer temperatures, however, some moon jellies survive winter, giving them a head start to begin reproducing when the water warms up in the spring.
- Overfishing – fish larvae and moon jellies compete for copepods, the tiny innumerable crustaceans that feed on plankton. When fish and jellyfish compete, the growth of jellyfish is limited. Take away the fish – as we have in so many ways all around the world – and the jellyfish populations grow rapidly. To make matters worse, jellyfish like moon jellies will actually prey on fish eggs and larvae. When there aren’t that many moon jellies and other jellyfish, the fish larvae can compete for copepods. But there is some evidence that once the number of jellyfish gets above some threshold, they limit the ability of fish to reproduce, thereby slowing the return of a balance between fish and jellyfish.
- Fertilizer runoff – When agricultural and lawn and garden fertilizer runs into harbors and bays, it can lead to blooms in algae, dinoflagellates, and other microorganisms. This changes the food web in ways that favor jellyfish over fish.
The Moon Jelly – One of nature’s most adaptable creatures
The list above makes it clear that there are man-made changes going on that favor moon jellies. But give some credit to the jellyfish themselves for being able to exploit those changes. They can eat almost anything, from floating organic matter to copepods to fish larvae. Probably because they sting and are overwhelmingly made of water, only a few types of fish will bother to eat them. They are preyed on by sea turtles, but there are far fewer of those than there used to be.
Finally, moon jellies have one of the most complicated and adaptable systems of reproduction in the animal world. They have several ways of reproducing asexually, and a couple of pathways of sexual reproduction. This gives them enormous potential to increase population size rapidly and with great flexibility based on local conditions. Give these guys an opening and they will take advantage quickly. That’s why they are found all over the world and that’s why we are seeing more and more of them.
As interesting and beautiful as they are, the increase in moon jellies around the world is creating problems. They do sting and are therefore a nuisance to swimmers. When there are lots of them, they can clog water intake pipes, and gum up and weigh down fishing nets. And, as mentioned above, they may be delaying the recovery of overfished resources.
For Your Viewing Pleasure:
This page shows the stages from polyp to floating medusa for Aurelia. Click on next. The first five slides are moon jellies.
This youtube video, with rather overly dramatic sound track, shows the stages as well:
Ki, J-S., Hwang, D-S., Shin, K., Yoon, W. D., Lim, D., Kang, Y. S., Lee, Y., and Lee, J-S. 2008. Recent moon jelly (Aurelia sp.1) blooms in Korean coastal waters suggest global expansion: examples inferred from mitochondrial COI and nuclear ITS-5.8S rDNA sequences. – ICES Journal of Marine Science, 65: 443–452.
Uye, S. (2011). Human forcing of the copepod-fish-jellyfish triangular trophic relationship. Hydrobiologia, 666(1), 71-83.
Dong, Z, Liu, D, & Keesing, J. (2010). Jellyfish blooms in china: Dominant species, causes and consequences. Marine pollution bulletin, 60(7), 954-963.
Lynam, C, Hay, S, & Brierley, A. (2004). Interannual variability in abundance of north sea jellyfish and links to the north atlantic oscillation. Limnology and oceanography, 49(3), 637-643.
Vagelli, A. (2007). New observations on the asexual reproduction of Aurelia aurita (Cnidaria, Scyphozoa) with comments on its life cycle and adaptive significance. Invertebrate Zoology, 4(2): 111-127.