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A hummingbird with an open heart surgery scar?

hummingbirdThe Question: Can you tell me what might have caused the wound on this hummingbird? It looks like it had open heart surgery!

Submitted by: Irene, Ontario, Canada

(click on photos and graphics to expand)

The Short Answer: Irene, that’s a brood patch on a female ruby-throated hummingbird (Archilochus colubris).  Birds that incubate eggs lose their breast feathers when they are nesting.  Otherwise, feathers, which make great insulation, would prevent the eggs and chicks from being warmed as efficiently by the parent. So what you saw on this hummingbird is perfectly normal and nothing to worry about.  This time of year, the parents don’t need the insulation, so losing some breast feathers for a while doesn’t bother them.  They’ll grow back before the weather gets cold in the fall.

hummingbirdGreat photos, by the way!!

More Information: The loss of breast feathers is triggered by hormones released at the time of egg laying. Some birds don’t ever lose breast feathers for incubation. This includes species like the brown-headed cowbird (Molothrus ater), which lays its eggs in the nests other birds, birds like gannets that warm eggs with their feet, and the males of many species, including ruby-throated hummingbirds, in which the female does all the incubation work. Female ruby-throated hummingbirds build the nest of plant material and spider webs and carefully camouflage it, a process that takes a week or more. They lay the eggs, of course, typically two. They sit on the eggs, warming them against the bare skin of the brood patch, for 12-14 days. Once the eggs hatch, it takes 18-20 days for the chicks to begin flying. The female feeds the chicks for another 4-7 days after they leave the nest and then they’re on their own. As with many birds, the chicks actually weigh more than the adults at that point, but their weight drops sharply until they get good at feeding themselves. While female ruby-throated hummingbirds are doing all that chick-rearing work, the males are defending food sources and trying to attract additional females to mate with – and keeping all their breast feathers the whole time. It’s only ever the females that look like they’ve had heart surgery.

Sources: Weidensaul, Scott, T. R. Robinson, R. R. Sargent and M. B. Sargent. (2013). Ruby-throated Hummingbird (Archilochus colubris), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/204

Gill, F. B. (1990). Ornithology. New York: W.H. Freeman.

Cite this article as: Pelletier, TC. (July 17, 2014). Ask a Naturalist.com: A hummingbird with an open heart surgery scar? Accessed on July 24, 2014. http://askanaturalist.com/a-hummingbird-with-an-open-heart-surgery-scar/

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Can caterpillars fly?

The Question: I just saw a caterpillar flying on a silk thread. It was moving along with the air current about a meter (3 feet) off the ground. It was suspended on a long thin thread with no apparent ‘parachute’ on the end. Eventually it descended to the grass level and walked off. I was not aware caterpillars could do this.
Submitted by: Mark, Berkshire County, United Kingdom

(click on photos and graphics to expand)

gypsy moth caterpillar

gypsy moth caterpillar

The Short Answer: Yes, caterpillars can “fly,” although insect scientists actually use the more whimsical term “ballooning” to label the behavior. And if you see a caterpillar flying or ballooning again, I encourage you to take some pictures and video, because although it is a fairly common phenomenon, I was unable to find any good pictures or videos I could share. If you search for “flying caterpillar,” most of what you’ll find is larger caterpillars dangling in mid air. This is not true flying or ballooning, however. Instead, this is a behavior that usually occurs when a caterpillar falls off a branch or drops off a branch deliberately to escape a predator. The caterpillar releases a silk line as it falls, and then climbs back up to return to its branch. I wrote about this previously in an article about dangling caterpillars.

What you’re talking about, however, sounds more like true ballooning. Some species of moth, including the notorious gypsy moth (Lymantria dispar), use ballooning as a way to disperse. Right after the eggs hatch, the tiny caterpillars drop down on a line of silk, sometimes only a few centimeters long, but in some cases a meter long, and then wait for the wind to break the thread. At that point, the caterpillar is carried along till it lands in another plant or on the ground.

Dr. James Bell, a senior research scientist who studies insect behavior at the Rothamsted Research agricultural center in England, says conditions have to be just right for this to work.  “For the neonate caterpillars to be successful, the right meteorological conditions have to be present.  The weather has to be warm, with rising air, and wind speed needs to be less than three meters per second.”

You might think ballooning is not a very effective way to disperse, and in some ways you’d be right. The tiny ballooning caterpillars don’t seem to have any control over where they land. They just let go and hope. And the fact is that quite a few end up on the ground. When that happens, they may quickly dry out and starve.

By chance, some do land on the right trees. Those caterpillars, feeding on their preferred food, tend to grow faster and produce more eggs than those that land on less suitable food plants. In some species, the caterpillars that land on the wrong trees have the ability to launch a second time. So the caterpillars may start out randomly distributed on nearby plants, but since the ones that land on the right food source stay put and the ones that land on the wrong food source sometimes get lucky on the second ballooning, the end result is higher densities on the correct plant, despite having no direct control over where they land.

The other thing that helps is that the caterpillar species that use ballooning to disperse are nearly all generalists about food plants. They usually have a preferred food plant, but can survive and grow to become reproductive adults on many different food plants. Other moth species are often specialized to feed on a single host plant species, or only on the species within one plant genus or family.

Why Doesn’t Mom Pick the Spot: But all of this makes you wonder, why doesn’t mom moth do the dispersing and find the right food source the way most moth moms do? In most moths, adult males and females have wings. They find each other, they mate, and the female flies to the preferred caterpillar food source plant, lays her eggs, and the caterpillars hatch right onto their first meal.

In species that balloon, however, females are wingless. They feed on one plant until they reach adulthood. Flying males locate the females and mate with them. The females then lay eggs on the same plant. When the eggs hatch, some will stay put and others will balloon away to find a new food plant. There are conditions under which it seems that this is a very successful strategy. For example, if you are a moth that lives in a forest where most of the trees are your preferred food, then your odds of landing in a good place when you balloon are pretty good. If that particular habitat is also stable for long periods of time, it means dispersal never has to be very far – or very accurate.

The overwhelming majority of moth species disperse by flying, however, so ballooning is definitely a fringe method for dispersing, but under the right circumstances, it can work. Since females whose offspring disperse by ballooning don’t need to fly, they can use their energy to grow fatter and carry more eggs. Over the long run, females without wings may outcompete females that fly.

Extreme Ballooning – Ballooning has evolved multiple times in several families of moths. Some spider mite species and many species of spiders also independently evolved ballooning as a means of dispersal. Given that ballooning evolved multiple times, it must be a successful trick. The real stars of the ballooning world are spiders. While caterpillars and spider mites typically balloon only a short distance before landing on a plant or the ground, spiders can be lifted high into the air. Caterpillars and spider mites have never been collected in the air out at sea, but spiders can be found ballooning hundreds of kilometers from shore. When he was traveling the oceans on his journeys, Charles Darwin noted that spiders would often rain down onto the famous ship, The Beagle. And when new volcanic islands form in the ocean, often the first animals that show up are spiders that wafted there on a line of silk.

Interesting video on ballooning spiders – http://www.youtube.com/watch?v=kYPABcMzbEg

Cool video that shows a spiderling molting, and then shows ballooning spiderlings – http://www.youtube.com/watch?v=aICZqRY3_d4

Sources:

Bell, J R, Bohan, D A, Shaw, E M, et al. (2005). Ballooning dispersal using silk: World fauna, phylogenies, genetics and models. Bulletin of entomological research, 95(2), 69-114.

Barbosa, P, Krischik, V, & Lance, D. (1989). Life-history traits of forest-inhabiting flightless lepidoptera. The American midland naturalist, 122(2), 262-274.

Cite this article as: Pelletier, TC. (June 16, 2014). Ask a Naturalist.com: Can caterpillars fly? Accessed on July 24, 2014. http://askanaturalist.com/can-caterpillars-fly/
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Can I swim with beavers?

The Question: I’ve heard that it might not be healthy to swim in a pond with an active beaver colony in it, as something is in the water from the beaver that can be bad for humans. Do you know if this is so? We have a large beaver pond with an active colony, and deep water at least 30 feet out from the dam, and we’d love to swim in it. Are there any tiny worm-like parasites we should be worried about as well? I couldn’t find any information online about this.

Submitted by: Faye, Minnesota, USA

(click on photos and graphics to expand)

The Short Answer: Before I begin to answer, I should say that I am not a doctor and not a qualified public health official. There are dozens or maybe hundreds of diseases that can be contracted from “surface waters,” meaning lakes, rivers, ponds, etc. Some of them are caused by worms, but giardiasis and cryptosporidiosis, the two most commonly associated with beavers (Castor canadensis in North America, Castor fiber in Eurasia), are caused by protozoan intestinal parasites (Giardia sp. and Cryptosporidium sp. respectively), which are spread through feces. Because beavers poop in the water, they can release the infectious cysts of the organisms. If you swallow the water, you may become infected. Unfortunately, you only have to ingest a small number of cysts to become infected.

BeaverCommon knowledge associates giardiasis and beavers so closely that people often call the disease “beaver fever.” However, it’s not clear that beavers very often contaminate people with Giardia. In fact, it seems that Giardia species tend to specialize. So the Giardia that most commonly infects beaver is different from the one that infects people. However, most Giardia have some ability to infect organisms other than their primary host, and you can find human-type Giardia in beavers. But the evidence suggests that when it is found in swimming waters and in beavers, the most common source of the human-type Giardia is not the beavers but people. Typically, it’s from untreated sewage that gets into the water or from fecal matter washing off people when they are in the water. For that reason, health officials recommend that people with diarrhea stay out of swimming waters.

Even so, swimming in beaver waters is not the most common way to get “beaver fever.” The largest number of cases are among small children in day care centers, who pass it among each other.

So if you want to know if a swimming area is safe, rather than look for a swimming hole with no beaver, you should probably look for one with no people – especially small people. The situation for cryptosporidiosis is similar. And while these diseases tend to be “self-limiting,” they are not fun, often causing severe diarrhea. One common hiker’s saying is that “While beaver fever won’t kill you, you might wish you were dead.”

When I asked Lihua Xiao, who is Chief of the Molecular Epidemiology Laboratory/WBDP of the Division of Foodborne, Waterborne, and Environmental Diseases for the United States Centers for Disease Control, for his opinion about swimming with beavers, he said flatly “I would not swim in a pond where beavers are active.”

I think that is a somewhat extreme view that would restrict you from the joy of swimming in most of the waters of Minnesota, but Dr. Xiao is one of the world’s foremost experts on these diseases and the organisms that cause them, and I am not. So you should weigh our opinions appropriately.

If you do decide to swim in your beaver pond, you should, as much as possible, avoid swallowing the water, and you should never drink untreated surface waters. The recommendation is to boil or use filters that specifically say they will remove Giardia. The cysts of Giardia and Cryptosporidium are somewhat resistant to chlorine, so don’t count on that. Boiling and filtration will also kill or remove most other waterborne diseases and parasites at the same time, including any worm-like parasites.

MuskratFear the muskrat: A study that tested beaver and muskrat (Ondatra zibethicus) in Pennsylvania and New Jersey for Giardia and Cryptosporidium found that out of 10 beaver tested, none were infected with Cryptosporidium and only one was infected with Giardia. The muskrat were a different story. Nearly 90% were carrying one or the other of the parasites and nearly a third were carrying both. So on the basis of this study, it might make even more sense to avoid waters with muskrat than with beavers. Of course, beaver and muskrat are often found together in Minnesota and most other places, so that doesn’t help much.

To Get More Info: The Center for Disease Control’s Giardia page: http://www.cdc.gov/parasites/giardia/gen_info/faqs.html

Lifecycle of Cryptosporidium from CDC: http://www.cdc.gov/parasites/crypto/biology.html

Lifecycle of Giardia from CDC: http://www.cdc.gov/parasites/giardia/biology.html

Very informative page from the Washington State Department of Fish & Wildlife on beaver, how to live with them, and how to discourage them if that’s your goal: http://wdfw.wa.gov/living/beavers.html

Sources:

Monis, P.T. & Thompson, R.C.A. “Cryptosporidium and Giardia-zoonoses: fact or fiction?” Infection, Genetics and Evolution 3 (2003): 233–244.

Bitto, A, & Aldras, A. (2009). Prevalence of giardia and cryptosporidium in muskrats in northeastern Pennsylvania and New Jersey. Journal of environmental health, 71(8), 20-26.

Feng, Y, & Xiao, L. (2011). Zoonotic potential and molecular epidemiology of giardia species and giardiasis. Clinical microbiology reviews, 24(1), 110-40.

Cite this article as: Pelletier, TC. (June 6, 2014). Ask a Naturalist.com: Can I swim with beavers? Accessed on July 24, 2014. http://askanaturalist.com/can-i-swim-with-beavers/

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What is this Costa Rican moth/butterfly?

Costa Rican mothThe Question: We saw many moths and butterflies in La Selva Verde in Costa Rica. This big one has a strange structure! Can you help us with finding a scientific name?
Submitted by: Fred, Belgium

(click on photos and graphics to expand)

The Short Answer: This is Titaea tamerlan, one of the group of moths known as silk moths (Saturniidae). It is found in Central and South America, from Mexico to Peru. The projections at the bottom of the wings identify this as a male. The family Saturniidae contains the world’s largest moths, and Titaea tamerlan is a good representative, with females about 12.5 cm (5 in.) across and males a bit smaller. After mating, females lay 5-10 eggs on the undersides of leaves of trees in the mallow family (Malvaceae), including the kapok tree (Ceiba pentandra), silk floss tree (Ceiba speciosa), and pachote (Pachira quinata).  The eggs hatch about six days later and the caterpillars feed on the tree leaves.  Over the course of about a month, the caterpillars go through several dramatic changes, beginning thin and spiky and ending plump and smooth.  (To see the various stages, you can click here to go to a website that features Costa Rican butterflies and moths.)  Eventually, the caterpillars burrow into the ground, where they pupate and later emerge as adult moths.  The adult moths only live 6-9 days and don’t eat at all.

Moth or Butterfly: If you’re not sure whether something is a moth or a butterfly, the easy answer is that they are all moths. If you look at the evolutionary tree of the Lepidoptera, the insect order that includes both moths and butterflies, you will see that all the butterflies come off one small side branch of the tree. If you go to the Lepidoptera page of the website Tree of Life, click on Neolepidoptera, and then Ditrysia and you’ll finally see that the butterflies are all in the Papilionoidea, which is just one of 126 families in Lepidoptera.  There are somewhere around 15,000-20,000 species of butterflies, out of a total of 174,250 catalogued species of Lepidoptera (moths and butterflies). So butterflies are a large group, but they are still a minority in the Lepidoptera. The truth is that the Lepidoptera is mostly about moths, with a colorful and interesting subset of butterflies.

moth with fuzzy antennae

moth with fuzzy antennae

butterfly with club antennae

butterfly with club antennae

If you are looking at a moth/butterfly type creature, and you want to know which it is, two rules will generally give you the answer. Butterflies are active during the day and moths are active at night, and butterflies are every color in the rainbow, and moths are generally brown, gray or white. Use those two rules, and you’ll be right most of the time. But there are exceptions. There are moths that are active during the day, and there are beautifully colored moths. There are also drab- colored butterflies that are only active at night. The accurate way for us non-lepidopterists to make a determination is to look at the antennae. The antennae of butterflies are simple and thin, ending in a thicker bulb or club shape. The antennae of moths can be almost anything else, although most of them have a somewhat hairy or fuzzy appearance.

Moths, including the ever popular butterfly subgroup, are an evolutionary success story. Nearly one out of every five animal species that has been classified and described is a moth or butterfly. This percentage is almost certainly skewed upwards by the fact that these creatures are relatively easy to catch and catalogue, but still, there are a lot of moths out there in the world.

Sources:

Thanks to Ryan St. Laurent, at BugGuide.net for the ID on this moth (although, the BugGuide people warned me that they really only do insects of North America).  Thank you to Dr. Richard S. Peigler at the University of the Incarnate Word in San Antonio, TX for his help with information on Titaea tamerlan.  And thanks to Dan Janzen, biologist at the University of Pennsylvania, for his help and the great pictures of Titaea tamerlan larvae on his site Caterpillars, pupae, butterflies & moths of the ACG.

Mora, C, Tittensor, D P, Adl, S, et al. (2011). How many species are there on earth and in the ocean? PLoS Biology, 9(8), e1001127.

Cite this article as: Pelletier, TC. (May 13, 2014). Ask a Naturalist.com: What is this Costa Rican moth/butterfly? Accessed on July 24, 2014. http://askanaturalist.com/what-is-this-costa-rican-mothbutterfly/

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What are these jelly dots under rocks?


jelly dot on rocksThe Question:
In the center of the attached photo you will see a clear soft glob which I suspect is some sort of egg mass. There were between one and three of these on several rocks I picked up in fast water on a trout stream in southern West Virginia. Do you have any idea what these are?
Submitted by: Harry, West Virginia, USA

(click on photos and graphics to expand)

Physa_acuta_001 The Short Answer: According to Robert Dillon, who studies the genetics, evolution and ecology of mollusks at the College of Charleston, this is almost certainly the egg mass of a freshwater snail in the genus Physa, probably Physa acuta. Physa snails are commonly called bladder snails, tadpole snails or pouch snails. They are found in nearly every body of freshwater. Dr. Dillon has nominated Physa acuta as “the world’s most cosmopolitan freshwater gastropod.”

“They can be found anywhere and on all six continents,” he notes. “They typically reach maximum abundance in calmer waters – ponds, lakes, river backwaters – and especially in disturbed or trashy environments.” His one hesitation about declaring that the egg mass Harry found is definitely Physa acuta is that a clear, clean trout stream would not be Physa acuta’s most common habitat.

Physella_acuta_A_MRKVICKA Each Physa acuta egg mass, which is a little less than a centimeter across (3/8 inch) contains 15-30 eggs, which hatch in 7-10 days into tiny snails. These snails feed on algae, detritus and infusoria, the coating of algae, bacteria, microorganisms and microscopic animals that coat the surface of nearly everything in freshwater. Adult Physa acuta aren’t very big, rarely reaching a centimeter (3/8 inch) in length. They are, however, prolific, laying an egg mass about every other day. The population can double in seven days, and in its lifetime, each snail will produce over 800 offspring, which explains why some aquarium hobbyists hate them. They are very common in aquariums and their colonizing of aquariums is one way that Physa acuta has been spread all over the world from its original home, which was probably in North America.

This video shows a Physa snail cruising around an aquarium: https://www.youtube.com/watch?v=LclVg12aC5Q

This neat time lapse video shows a Physa egg mass, with a number of tiny snails developing and then crawling away: https://www.youtube.com/watch?v=a9Z0k0RI-s4

It’s a Boy, No it’s a Girl … Wait, it’s Both: Dr. Dillon likes to call Physa acuta “the fruit fly of malacology,” malacology being the study of mollusks. What he means by that is that they are a handy species for study in the lab. They are small, easy to keep, multiply readily, and don’t cost much to feed. And Physa acuta is particularly useful for studies about reproduction, and especially about hermaphroditic reproduction. Physa acuta is a “simultaneous hermaphrodite,” meaning that it can produce eggs and sperm at the same time.

But when baby Physa snails develop, they become sexually mature as males first, at about five weeks and then they mature as females at about seven weeks. From that point on, when they meet another snail, they can adopt either the male role or the female role. Some hermaphroditic animals play both roles at the same time, but in Physa snails, it is physically impossible for each snail to inseminate the other at the same time. Probably because it requires fewer resources of energy and nutrition to create sperm than it does to create eggs, when two Physa snails meet, they may wrestle over who gets to be the male.

As Dr. Dillon describes it “They ONLY want to be male, and will engage in all sorts of fighting to do so.  But immediately after mating as males, they become passive.”

If they encounter another snail before they rebuild their sperm stores, they will end up in the female role. In a population where the snails are bumping into each other frequently, this results in a rough pattern of alternation of mating as a male, then as a female, then as a male again, etc. The snails can store sperm from a mate, however, and a single mating can provide enough sperm to last for dozens of egg masses. This helps to explain why they have spread so rapidly around the world. The introduction of a single snail into a body of water can result in that snail producing hundreds of baby snails from its stored sperm. And if that stored sperm is a collection of sperm from various matings, the new population will even contain a fairly healthy level of genetic diversity.

The other odd thing about Physa snails is that they are capable of fertilizing themselves. If baby snails are isolated from other snails, they will begin laying eggs at about 12 weeks. Self-fertilized eggs are less likely to hatch and less likely to survive, probably because of deleterious recessive genes carried by the parent snail, which are then expressed at high levels in highly-inbred offspring.

Physa shellHow Can an Animal With No Hands be Left-handed: If you hold a snail with its peak pointing upward and the opening facing you, you’ll notice that in most snails the spiral of the shell leads to an opening on the right. In some snails, including Physa snails, the opening is to the left. Right-handed snails are described as “dextral” and left-handed snails are “sinistral.”

If you pick up a small snail in your local pond or stream – or your aquarium – and you’re unsure whether it a Physa snail, one strong clue would be to check if it is left-handed.

Sources:

Dillon, RT, McCullough, TE, & Earnhardt, CE. (2005). Estimates of natural allosperm storage capacity and self-fertilization rate in the hermaphroditic freshwater pulmonate snail, physa acuta. Invertebrate reproduction & development, 47(2), 111-115.

Wethington, AR, & Dillon, RT. (1997). Selfing, outcrossing, and mixed mating in the freshwater snail physa heterostropha: Lifetime fitness and inbreeding depression. Invertebrate biology, 116(3), 192-199.

Facon, B, Ravigne, V, & Goudet J. “Gender-role alternation in the simultaneously hermaphroditic freshwater snail Physa acuta: not with the same partner.” Behavioral ecology and sociobiology 62.5 (2008):713-720.

Cite this article as: Pelletier, TC. (May 2, 2014). Ask a Naturalist.com: What are these jelly dots under rocks? Accessed on July 24, 2014. http://askanaturalist.com/what-are-these-jelly-dots-under-rocks/

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