millipede

What is this bright green string of eggs? – Part 3

This is part three in a three-part series about photos of bright green eggs first submitted to AskaNaturalist.com in the summer of 2014. The photos came from a reader in Nova Scotia and another in Maine. To read part 1, click here. To read part 2, click here.

string of green eggs and tape measure

Nova Scotia “string of bright green eggs”

egg string - maine - 800

Maine “jelly blob”

Previously on “bright green string of eggs”: Two independently submitted strings of bright green eggs or something like eggs, from Nova Scotia and Maine, July-Aug 2014. In Part I, we considered amphibian eggs, algae and snails. In Part II, we rejected all those possibilities and came around to chironomids – insects known as “non-biting midges.” Some chironomid species lay their eggs in water in gelatinous, spirally organized egg mass strings that look similar to the Nova Scotia and Maine eggs. There was a nagging problem, however, in that in two cases where someone hatched out one of these egg masses, the hatchlings had six legs, whereas the larvae of chironomids are legless.

Still we decided chironomids was the best answer … but wait ….

Chironomid larvae with legs?: There are strong similarities between these egg masses and those of some chironomids as the photo . But the photos Nancy from Maine had taken of her hatchlings clearly showed six legs – and chironomid larvae don’t have legs. That incongruity made me hesitant to declare victory and write up the chironomid answer. So I kept stalling …

Then, just when I finally decided I had to write it up and move on, I got a message from Charley Eiseman, who contributes to BugGuide.net and who has his own insect-related blog called Bug Tracks. Charley is a naturalist and author who co-wrote Tracks & Sign of Insects and Other Invertebrates. His book is on my Christmas wish list and I’ll do a review of it once I have it in hand. It sounds uniquely useful.

Charley responded to a photo I had placed on BugGuide.net weeks before that showed the egg mass and the hatchlings and asked for confirmation that the egg mass was chironomid. Charley’s response to my photo post said, “Well, as far as I know, donut-shaped egg masses are unique to caddisflies in the genus Phryganea. Also, chironomids, like most flies, have elongate eggs, whereas these are spherical, which is typical of caddisflies.”

I read this with great excitement because Charley’s identification would explain the six-legged hatchlings.

Adult Phryganea caddisfly

Adult Phryganea caddisfly

Caddisflies are insects that share with chironomids the trait of having their larvae develop in bodies of fresh water. Although the larvae of some of the approximately 12,000 caddisfly species are predatory, most caddisfly larvae feed on detritus, plant material, and algae. The Caddisfly order (Trichoptera) is related to the order that includes moths and butterflies (Lepidoptera), and you can see that resemblance in moth-like adult caddisflies and also in the fact that the juveniles go through a pupal stage the way that moths and butterflies do. In the case of caddisflies, the pupa is formed underwater, and the adult crawls out, floats to the surface and flies away. After the adults mate in the summer, they lay their eggs in the water. And some caddisflies in the genera Phryganea and Agrypnia lay strings of gelatinous, spirally organized egg masses that are characteristically looped or donut-shaped.

And the larvae, when they hatch, have six legs!

Phryganea caddisfly larvae

Phryganea caddisfly larvae

The larvae of most species build a long thin house by using silk to attach plant material, sand and other objects together. The larva crawls inside and wears the house pretty much round the clock nonstop until it is ready to pupate. The fact that they are very uncomfortable out of their house is shown in this somewhat humorous video of two caddisfly larvae competing for the same house: https://www.youtube.com/watch?v=h-9Lu9f5tEE. You can read my previous article about caddisflies by clicking here.

To make what has been a long story a little bit shorter, after checking with a couple of caddisfly experts and looking at illustrations of caddisfly egg masses that seem very similar to those of the egg masses from Nova Scotia and Maine (as well as the ones I came across from Vermont and Montreal), I am prepared to say that Charley’s diagnosis of caddisfly eggs best fits all the evidence.

One key piece of evidence – remember my blatant foreshadowing – is that, as Charley said in his BugGuide.net response, chironomid eggs are nearly always elongated or oval shaped. Caddisfly eggs, on the other hand, are nearly always spherical. And now, if we go back to the eggs from GoldFish Garage, and zoom in, you’ll see they are elongated.

egg masses from Nova Scotia and Maine

The eggs in our Nova Scotia and Maine egg masses, on the other hand, are spherical, as shown in this zoomed in photo.

Maine’s list of caddisflies includes several species in the genus Agrypnia and Phryganea, as does Nova Scotia’s. We don’t know for sure the two egg masses came from the same species, of course. The egg masses of such closely related species probably look very similar.

But having confirmed that there are Agrypnia and Phryganea species in Maine and Nova Scotia, I am finally, at long last, confident in saying that the egg masses submitted by Emily in Nova Scotia and Nancy in Maine (as well as the eggs from Vermont on Robyn’s Pond Page) are almost certainly caddisfly eggs.

Phew! This was a fun one for me, but I apologize to Emily and Nancy, who had to wait so long for an answer.

Tying up loose ends:

Snails – “But what about the snails?” you might ask. Remember that the person who found the similar egg mass in Montreal insists that baby snails hatched from it. As we’ve seen, two not very closely related insect groups have evolved very similar egg masses, so it’s not out of the realm of possibility that a group of snails have also evolved a similar egg mass, as Rob Dillon discusses in his blog posts about this same subject. As far as I can tell, there are no snails known to lay this kind of egg mass, however, so I’m inclined to suggest that the baby snails were hitchhikers. I feel a tad hypocritical in saying this, because when the same kind of explanation was offered for the presence of six-legged larvae coming from an egg mass that was supposed to be chironomids (which don’t have legs), I strongly disagreed. But I have only a third-hand connection to the person who had snail hatchlings, so I’m more willing to discount that observation. I don’t know where the snails came from, but I don’t think it was from the egg masses.

Size of egg masses – One of the reasons it was hard to accept chironomids as the layers of these egg masses is the size of the egg masses compared to adult midges. As the ruler included by Emily in her photo of the egg mass from Nova Scotia, these egg masses are more than two inches (5 cm) long. Although a few of the larger chironomid species can be 10 mm (3/8 inch), most are smaller than that. It was hard to imagine how a female chironomid adult could lay something so much larger than itself. Agrypnia and Phryganea caddisflies are considerably larger, up to 25 mm (1 in.) in length, but still the egg masses are considerably larger than the caddisfly female who lays it. It turns out that in both the chironomids and the caddisflies, the eggs are laid with only a sort of chemical latticework, which begins to swell as soon as it hits water, forming the tough gel that protects the eggs.

Academic opportunity – I lost track of how many people told me, “Hardly anyone studies the eggs.” Or “Very little is known about the eggs.” I heard this about freshwater snails, about chironomids and about caddisflies. If there’s a young biologist out there who is looking for an area in which to add to our knowledge of nature, this would be an easy area in which to make a permanent mark. I’m planning to look for egg masses myself next summer and hatch some out. I’ll keep you posted.

That striking green color – One other mystery remains. Why are some of these eggs so green? In nature, that bright green color is almost always a sign of chlorophyll. In some species of amphibians, the eggs have a symbiotic relationship with algae. The microscopic algae benefit by living in the protection of the egg mass gel. The eggs benefit because the algae release oxygen, something that is critical to eggs that are stuck in the deep middle of an egg mass. Oxygen diffuses through the mass from the water, but if you can get a little extra from some symbiotic algae, it’s a bonus.

So is that what’s happening with these bright green caddisfly eggs? Are they symbiotic with algae? And the green chironomid eggs as well? And why were Nancy’s eggs green the first time she saw them and more brown the second time. As far as I can tell, no one has studied this. Another opportunity for a biologist to take up.

Two mysteries with one answer – When Charley Eiseman was poking around on AskaNaturalist.com, he came across another article I wrote: “Donut blob that stumped the experts ….” This was about a gelatinous donut-shaped object a reader found in a Maine lake. Charley offered the possibility that the translucent donut might be what’s left of a caddisfly egg mass once the larvae have hatched and crawled away to build their little houses. This is by far the most reasonable explanation I’ve heard for this donut blob and I’m inclined to think that Charley has solved that mystery as well. Caddisflies are everywhere!

Thank yous: Thank you to Rob Dillon for all his help and his interest in this case, which helped keep me pushing for a good answer. Thanks also to Charley Eiseman for the answer to the mystery, Alexander Huryn, aquatic ecologist at the University of Alabama, who also suggested caddisflies, and to caddisfly experts John Morse at Clemson University , David Houghton at Hillsdale College and Ralph Holzenthal at the University of Minnesota for help in providing evidence that supports the Phryganea/Agrypnia caddisfly answer. I also greatly appreciate help with chironomids from Professor Ali Arshad at the University of Florida, independent chironomid expert John Epler, David at GoldFish Garage, Bohdan Bilyj, and Jon Martin at the University of Melbourne.

Thank you also, to Robyn Rhudy at FishPondInfo.com and J. Trevor Vennata, who studies snails at the University of Minnesota.

Sources:

http://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=1163&context=aes_techbulletin, The Caddisflies (Trichoptera) of Maine, Excepting the Family Hydroptilidae, R. L. Blickle and W. J. Morse, Bulletin T-24 November 1966.

Wiggins, G. (1998). The caddisfly family Phryganeidae (Trichoptera). Toronto: Published in association with NRC Research Press, Canada Institute for Scientific and Technical Information by University of Toronto Press.

Rasmussen, A.K., & Morse, J.C. 2014. Distributional Checklist of Nearctic Trichoptera (Summer 2014 Revision). Unpublished, Florida A&M University, Tallahassee. 487 pp.  [Available at http://www.Trichoptera.org]

Hinton, H.E. 1981. Biology of Insect Eggs. 3 volumes. Pergamon Press, Oxford.

Hickin, N. (1968). Caddis larvae; larvae of the British Trichoptera. Rutherford [N.J.: Fairleigh Dickinson University Press.

Frost, S. (1959). Insect life and insect natural history (2d rev. ed.). New York: Dover Publications.

Cite this article as: Pelletier, TC. (December 19, 2014). What is this bright green string of eggs? – Part 3 Retrieved from http://askanaturalist.com/what-is-this-bright-green-string-of-eggs-part-3/ on December 21, 2014.

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What is this bright green string of eggs? – Part 2

This is part two in a three-part series about photos of bright green eggs first submitted to AskaNaturalist.com in the summer of 2014. The photos came from a reader in Nova Scotia and another in Maine. To read part 1, click here. To read part 3, click here.

string of green eggs and tape measure

Nova Scotia “string of bright green eggs”

egg string - maine - 800

Maine “jelly blob”

Previously on “bright green string of eggs”: Two independently submitted strings of bright green eggs or something like eggs, from Nova Scotia and Maine, July-Aug 2014. First thought was amphibians symbiotic with algae. Amphib expert says emphatically, “No!” He suggests algae. Algae expert says “No. Maybe snail eggs?” Rob Dillon, snail expert, says he received a similar photo several years ago, and the person who sent it hatched the eggs and got tiny baby Lymnaea (Bulimnea) megasoma, a freshwater snail of the northern United States and southern Canada.

So the answer to who laid these eggs: snails … but wait ….

Snails with legs?: Shortly after I sent the bright green string photos to professor Dillon, I was doing an image search for various combinations of green, string, eggs, etc. I came across this page: http://www.fishpondinfo.com/egg.htm, where Robyn Rhudy, who describes herself as “Specializing in Nature, Animals, Fish, and Ponds,” has some good information on how to identify various egg masses to be found in freshwater. When I emailed Robyn and asked if she knew what the egg masses from Nova Scotia and Maine were, she said she didn’t, but that she had seen something like this before. She directed me to the bottom of her page about the aquatic insects you can find in a backyard pond, where she describes how a reader sent her a photo and this message:

“I found some eggs in a neighbor’s pond today (July 25) here in central Vermont. The clear 3/8″ diameter strand is configured in a ring about the size of a hair elastic, with hundreds of tiny (salt grain size) green dots in a very orderly spiral pattern along the strand. The ring was attached to a submerged rock and is very elastic….”

“The diameter of the elastic band (which does not break up when handled and will stretch to fit over my hand) is about 1/4″ – 3/8″ when un-stretched. It is about the size of a hair elastic but thicker. It is hard to tell how big the actual egg white part is because they are arranged in a ring and not separate. And the coil of green dots is very uniform and regular. As you can see, I’ve scraped the strand off the rock and have it in a jar to see what hatches….”

This description matches the two bright green strings I previously described in Part 1, including the key fact of coming from the northeastern US/Southeastern Canada region. The only difference is that in the photo submitted to FishPondInfo, the string is less green and more brownish. And the key thing is that when Robyn’s reader hatched the eggs, she drew a picture of what hatched. The creature she drew has six legs and a long abdomen. Definitely not a snail. The only creatures on this earth with six legs are insects, and the drawing looks like many aquatic insect larvae.

chironomus midge

Chironomid midge

With this new information, I renewed my search, but in an insect direction. I soon latched onto the chironomids as a possible source for the gelatinous, spirally organized egg mass . The family Chironomidae includes at least 20,000 species of small flies found worldwide. Chironomids are in the suborder Nematocera, which also includes our all-too-familiar mosquitoes and blackflies as well as midges. Unlike many other midges, however, chironomids don’t bite. In fact, they are often descriptively called “non-biting midges” and many chironomids probably don’t feed at all as adults. That doesn’t mean they don’t annoy people, however. Chrironomids are famous for hatching simultaneously in plague-like numbers from some bodies of water, to the extent that they cover surfaces and ruin summer lakefront parties, and when they die simultaneously, they can form smelly piles of tiny rotting corpses.

Before we wish these tiny creatures off our lovely planet, however, we should acknowledge that the enormous numbers of chironomid larvae, feeding on detritus and microscopic organisms, form a key link in the food chains of nearly every body of freshwater on the globe. They can survive in clean water and they help to clean dirty water. Many species that live in low oxygen conditions in mud have a kind of hemoglobin in their body fluid that helps them pull oxygen from the water. Because hemoglobin makes their transparent bodies look pink or red, these larvae are often called “bloodworms” when they are sold as food for aquarium fish.

In fact, as I looked for confirmation that these egg masses were laid by chironomids of some kind, I came across this photo on the website of someone who raises goldfish as a hobby: http://goldfishgarage.blogspot.com/2014/05/chironomid-bloodworm-egg-mass.html.

On that site, there is a photo of egg mass that looks very similar, in that it has spirally arranged eggs in a gelatinous string. It’s not exactly the same, but it seemed close enough to offer support for the chironomid idea. And when I asked David, who runs GoldfishGarage.com, he confirmed that he raises chironomids in his garage, as “bloodworm” food for his goldfish.

On his site, David also has a great video that shows the egg mass developing and tiny “bloodworm” chironomid larvae hatching. https://www.youtube.com/watch?v=VtNB6wYzas4#t=115.

Score one for chironomids as the layers of the Nova Scotia and Maine egg masses.

For confirmation, I sent the photos of the Nova Scotia and Maine egg masses to a handful of chironomid experts and asked for their opinions. The answers ranged from “probably” to “definitely!” with the consensus leaning toward the genus Chironomus. And an image search for “Chironomus egg mass” shows several photos of egg masses that look like David’s Goldfish Garage photo and very similar to the egg masses from Nova Scotia and Maine and from Robyn’s Pond Page.

Maine egg mass with hatchlings

Maine egg mass hatching

Ali Arshad, one of the chironomid experts I contacted, suggested that I write back to the AskaNaturalist readers who submitted the egg mass photos and ask them to put them in a bucket and see what hatches. I didn’t hear back from Emily in Nova Scotia, but Nancy from Maine was cheerfully willing to create a nursery for hundreds of mystery insects. She said the original egg mass had been put back in the lake, but she collected another one from her dock. And when it began to hatch a few days later, Nancy sent me this photo:

And that’s when the chironomid train went off the rails.

closeup of hatchling

hatchling

If you zoom in on one of the dozens of hatchlings coming from Nancy’s egg mass, you’ll see this:

The resolution is not great, but what is clear is that this tiny creature has six legs! But if you watch David’s video of chironomids hatching and look very closely, you’ll see that the larvae that hatch from his eggs – like all chironomid larvae – don’t have legs. They are long and skinny and have stumpy fake legs called parapods.

When I zoomed in and saw six legs on Nancy’s hatchlings, I knew these were definitely not chironomid larvae. And then I realized I should have paid more attention to the drawing that had been submitted to Robyn’s Pond Page, because it too has six legs. In fact, that’s what led me to think the egg masses belonged to insects in the first place. And the drawing is a reasonable representation of Nancy’s tiny hatchling.

I presented the six-legged evidence to chironomid experts who had expressed confidence that the eggs were chironomid, but while they agreed that the six-legged hatchlings were not chironomid larvae, they suggested that maybe the six-leggers were “hitchhikers” that didn’t really belong to the egg mass.

I wasn’t comfortable with that explanation because there were so many “hitchhikers” on Nancy’s egg mass, and for a while, I toyed with the idea that the six-legged hitchhikers were actually feeding on the egg mass. In fact, it occurred to me that maybe that could explain both the six-legged larvae coming from a chironomid egg mass and also explain how someone got baby snails from a similar egg mass (Remember the snails? If not, see Part 1). Maybe the snails were also feeding on the egg mass. None of the chironomid experts I contacted seemed to think much of that idea, however, so I dropped it and reluctantly accepted that these had to be chironomid egg masses.

I put aside the distracting detail of six-legged hatchlings, and prepared to make my determination: Chironomids it is …

But Wait, There is Another Possibility: In the third and final installment of this story, we find out that there is yet another possibility for who laid these egg masses, and it explains the six-legged larvae.

Sources: Sources and thank yous are at the end of Part III, coming soon …

Cite this article as: Pelletier, TC. (December 17, 2014). What is this bright green string of eggs? – Part 2 Retrieved from http://askanaturalist.com/what-is-this-bright-green-string-of-eggs-part-2/ on December 21, 2014.

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What is this bright green string of eggs? – Part 1

Because the sequence of events in the search for an answer to this question took some interesting turns, I’m departing from my usual format to write this answer as more of a diary. If you don’t find this format interesting, don’t worry, I’ll soon return to my regular format.

This is part one in a three-part series.  To read part 2, click here.  To read part 3, click here.

The First String of Green: In July, I received an email and photo from Emily from Nova Scotia:

string of green eggs and tape measure

Nova Scotia “string of bright green eggs”

“We are finding these slimy strings of bright green eggs (?) in the lake. They can be found on the wharf poles, but the ones in the picture were on the cord for the underwater thermometer. Any idea what they are from?”

Emily cleverly included a tape measure in the photograph, which is in inches, so it looks like the uncoiled length of this would be about 2 inches, or 5 cm. The picture is of fairly high resolution (also clever on Emily’s part), and when I zoom it in, you can see that it consists of individual green dots held in a matrix of gel about 3 mm wide. I was able to make a rough measurement of the individual green dots at about 0.4 mm or 400 microns. And although it’s a little hard to count them because they are three dimensional, I came up with about 140 eggs in a 1 cm section of the string.

The string seemed egg-like, and I know some amphibians lay strings of eggs, and some amphibian eggs have a symbiotic relationship with green algae, so my first thought was some kind of amphibian eggs. The individual dots seem too small to be amphibian eggs, but I wasn’t sure about that, so I sent the photo to an amphibian egg expert, who quickly assured me that it was not an amphibian egg mass. He speculated that it might be an alga.

spirogyra algae

Spirogyra algae

That seemed like a reasonable guess, given that the string in the photo looks superficially like the strings of colonial green algae in the genus Spirogyra, as shown in this photo. Spirogyra is much smaller, however, with strands more on the order of 0.1 mm or 100 microns wide. Still, it seemed worth a shot, so my next email was to John Wehr, a professor of aquatic ecology at Fordham University’s Louis Calder Center, and an expert in freshwater algae.

The Second String of Green: Before I heard back from Dr. Wehr, however, I received another email, this time from Nancy in western Maine. She sent me this photo, and said:

egg string - maine - 800

Maine “jelly blob”

“I found this jelly blob or loop in the water on the ladder to my boat in a fresh water lake. I thought it was a round blob but it was more of a loop. These dots were bright green in clear jelly. It was about the size of a quarter. I thought it was a solid round blob but when I moved it, it was actually a line about 2-3 inches (5-7 cm) long. What is it?”

As you can see from Nancy’s photo, what she found was very similar to what Emily found in Nova Scotia. Going on Nancy’s suggestion that the looped mass was about the size of a U.S. quarter (about 2.5 cm or 1 inch), the string seems to be about 4 mm wide, and the individual dots seem to be about 0.5 mm or 500 microns – certainly in the same ballpark as in the string from Nova Scotia. Again, I counted dots in a 1 cm length, and got 125 – pretty close to the 140 of the Nova Scotia string.

Since these two egg masses were so similar, were found under such similar circumstances, and at the same time of year in freshwater from the same part of the world, from that point on, I began to include both masses in my emails to experts, under the assumption that these were two examples of eggs laid by the same creature, or at least similar creatures.

A day or two later, I heard from Dr. Wehr, the algae expert. He said:

“It is hard to tell from this magnification, but they look to me like an egg mass of some animal, which has symbiotic algae in association with them. I am algae person, not a zoologist, but while they may not be amphibian eggs, perhaps they could be snail eggs. Hard to say. But the green color is very likely the algae associated with the eggs,. This is phenomenon very common with salamander eggs and the association is apparently beneficial to both the alga and the eggs.”

The First Answer – Snails:  The snail possibility seemed reasonable to me, and I happen to know a freshwater snail expert, Dr. Rob Dillon at the College of Charleston. Dr. Dillon had been extremely helpful to me in a previous article on the egg masses of Physa snails. So I sent him the photos from Nova Scotia and Maine. Here’s what he said:

“Yes, the gelatinous strings of bright green bodies depicted do indeed appear to be the egg masses of a large pulmonate freshwater snail, Lymnaea (Bulimnea) megasoma (click here for photo, middle of the page). Very little is known about this critter. Its range seems to be restricted to WAY up north – Manitoba, Ontario, Quebec, Minnesota, Wisconsin, Northern Michigan, Maine. As far as I know, the egg mass of L. megasoma has never been described. The only way that I myself am able to identify your photos is that I received an inquiry nearly identical to yours from Quebec back in the late summer of 2011, and was clueless at the time, and my 2011 correspondent hatched the doggone thing out, and sent me a follow-up photo of the juvenile snails.

Dr. Dillon admitted he was unable to explain the green color of the embryos. He agreed that it looked like an algal association, but he pointed out that as far as he knew, that kind of egg/algae association had never been documented in a freshwater snail. Still, it seemed like maybe we had an answer to the question of who laid these beautiful egg masses.

Or did we?

Wait, There is Another Possibility: In the second installment of this story, we find out that there is another possibility for who laid these egg masses, and the experts who give me that possibility are just as certain about it as Dr. Dillon. The plot thickens … to read Part 2, click here.

 

Sources: Sources and thank yous are at the end of Part 3, coming soon …

Cite this article as: Pelletier, TC. (November 19, 2014). What is this bright green string of eggs? – Part 1 Retrieved from http://askanaturalist.com/what-is-this-bright-green-string-of-eggs-part-1/ on December 21, 2014.

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Is this a dragon paw?

shredded turtle foot

found by the dog

The Question: Look what my dog dragged into our home! Can you help us identify who/what/where this claw came from?? It was about the size of my palm. My son says it looks like a dragon paw!

Submitted by: Susan, Wisconsin, USA

(click on photos and graphics to expand)

The Short Answer: The only wild animal in Wisconsin that this could possibly come from is a large snapping turtle. Three very similar species of snapping turtles are found only in the Americas, with a Central American version (Chelydra rossignonii) and a South American version (Chelydra acutirostrisI) joining our North American species (Chelydra serpentina). The larger alligator snapping turtle (Macrochelys temminckii), is in the same family, the Chelydridae, but its range doesn’t extend into Wisconsin.

The common snapping turtle is a large turtle, with a maximum length of about 45 cm (18 inches) and weight of about 20 kg (45 pounds) in the wild. Snapping turtles, like most turtles and reptiles, have generally been considered to exhibit “indeterminate growth.” In a species with indeterminate growth, individuals develop at a rate that is usually dependent on the amount of food available, and they typically continue to grow throughout their lifetimes, although at a much slower rate as adults. Most fish, for example, continue to grow as long as they live. Animals with “determinate” growth, on the other hand, include mammals and birds, which, if given enough food, grow at a fairly predictable rate until reaching a certain age, at which point they stop growing at all (except for gaining weight).

baby snapping turtle

baby snapping turtle

The generalization that all reptile species, including turtles, exhibit indeterminate growth is definitely not true, and as we’ve learned more about growth patterns, the picture has become more complicated, even for species that do exhibit indeterminate growth (more on that later). But it is mostly true that most snapping turtles grow throughout their lives. They grow much faster as juveniles, with a growth rate of about 1.5-3 cm per year (1/2-1 inch) for the first decade of life, but only about .2 cm per year (less than a 1/16 of an inch) after the age of about 20. This rate can vary quite a bit, depending on the amount of food and the length of the active season. The growth rate of snapping turtles in Algonquin Provincial Park in Ontario, for example, is about half that of more southern turtles in the first few years of life. And the farther north you go, the longer it takes for turtles to reach reproductive maturity.

If you search online, you can find estimates of the maximum age of snapping turtles that range from 30 years to 150. The 30 year estimate is undoubtedly wrong, and the 150 years may be extreme also. But turtles in general can be very long-lived. A recent study (Congdon et al., 2013) estimated that in some populations it would take 75 years after reaching maturity at the average growth rate of adult snapping turtles to reach the size of the largest turtles in the study. Adding that to the typical age of about 15 years at reproductive maturity gives an age of about 90 years for some of the largest turtles. This is a very rough estimate, but it suggests that some big snapping turtles have lived a long time – especially in the northern parts of the snapping turtle’s range, like Wisconsin, where turtles are likely to grow slowly.

Your “dragon paw” may have come from a turtle that hatched before the Great Depression.

It’s not surprising that snapping turtles live a long time if you look at their adult survival rate. By the time a snapping turtle reaches reproductive maturity, it is big enough and formidable enough to have very few natural predators. In fact, in many parts of North America, the biggest cause of mortality for snapping turtles is people:  boat propeller strikes, cars, and trapping by people for food.

If I had to take a wild guess on this turtle, given that your dog presumably found it in a suburban neighborhood, on land, it was probably hit by a car.  It may have later been torn apart by a coyote, a fox or your dog, but that’s probably not what killed it.  Dr. Justin Congdon, at the Savannah River Ecology Laboratory, has studied snapping turtles for more than 30 years. He gave me a different theory. “When people catch and butcher snappers, they typically cut off the head and feet first because reflex movements of the turtle make both a risk to the person doing the butchering. I suspect that’s what happened here and the dog found one of the discarded feet.”

common snapping turtle

common snapping turtle

More on Growth of Snapping Turtles: The Congdon et al. study looked at tagging and recapture data for nine species of North American turtles and found that all had indeterminate growth, in that about 80% of the individuals in the population continued to grow as adults. Interestingly, however, about one out of five adult turtles didn’t grow at all, even across time periods of a decade or more. So it appears that in these turtles, at least, the determinate/indeterminate dichotomy may not be so clear cut.

There is an evolutionary trade-off for animals with indeterminate growth that pits growth as a juvenile versus growth as an adult. The larger a female turtle, the more eggs she can lay. And generally, the larger a male turtle, the more battles he wins against other males in the competition to mate with females. It’s better to be bigger.

The trade-off occurs because once turtles begin mating, the energy expended by males competing and the energy expended by females to form and lay eggs slows their growth rate to a crawl (pun intended). Turtles that postpone mating so they can grow larger before they begin reproducing are at risk of being eaten or otherwise killed without ever producing any offspring. If they survive to that larger reproductive size, however, they may enjoy a long adulthood of prolific reproduction.

Turtles that begin mating at a smaller size, and then continue to grow slowly after that, may take a very long time to reach the size needed to produce large clutches of eggs or win their battles against other males. They are, however, more likely to have at least some offspring before something drastic happens to them.

Let’s hope your turtle had a long and successful reproductive life. Snapping turtles are still common across their range, but their numbers have decreased sharply in some places, as people overharvest them for consumption in the U.S. and shipment to other countries as well. Because few hatchlings make it all the way to adulthood, it will take a long time for snapping turtle numbers to recover to the levels prior to human harvesting.

Sources:  Special thanks to Dr. Ronald J. Brooks and Dr. Congdon for their help in reviewing this article.

Congdon, J D, Gibbons, J W, Brooks, R J, et al. (2013). Indeterminate growth in long-lived freshwater turtles as a component of individual fitness. Evolutionary ecology, 27(2), 445-459.

Galbraith, D A, Brooks R J, & Obbard M E. (1989). The influence of growth-rate on age and body size at maturity in female snapping turtles (chelydra-serpentina). Copeia, (4), 896-904.

Congdon, J D, Dunham A E, & Sels R. (1994). Demographics of common snapping turtles (chelydra-serpentina) – Implications for conservation and management of long-lived organisms. American zoologist, 34(3), 397-408.

Armstrong, D P, and Brooks, R J. “Estimating Ages of Turtles from Growth Data.” Chelonian conservation and biology 13.1 (2014):9-15.

Bennett, A M, & Litzgus, J D. (2014). Injury rates of freshwater turtles on a recreational waterway in Ontario, Canada. Journal of Herpetology, 48(2), 262-266.

Cite this article as: Pelletier, TC. (October 10, 2014). Is this a dragon paw? Retrieved from http://askanaturalist.com/is-this-a-dragon-paw-2/ on December 21, 2014.

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What is chasing these birds?

Mourning Dove

mourning dove

The Question: It’s VERY hot and humid here in Milwaukee – the cicadas and other insects seem to be the only ones enjoying it. Last night while walking my dog about dusk, I saw two different mourning doves being “chased” by something about 1.5 inches (4 cm) or so. The bird was flying quickly – in one case it had tried to land in a maple tree and then seems to have been sent off as this shape followed it. Could the tormenter be a cicada?

Submitted by: Lezlie, Wisconsin, USA

(click on photos and graphics to expand)

 

cicada killer

cicada killer

The Short Answer: Lezlie, it doesn’t seem very likely to me that it would be a cicada. I would rather expect the bird to be chasing the cicada than the other way around. But in trying to think of a 1.5 inch flying creature that a bird might wish to avoid and that might also be associated with a noisy population of cicadas, I first wondered whether it could it be a cicada killer, of which there are several species in the U.S. These large wasps (as large as 5 cm, 2 in) specialize in preying on cicadas. The female cicada killer stings a cicada to paralyze it and then stuffs the cicada down a hole dug in the ground. The cicada killer lays an egg on the cicada and when the egg hatches, the larva consumers the cicada. Female cicada killers tend to dig their holes in the same area, so in sandy, dry soil, you can sometimes see dozens or hundreds of these holes, especially when cicadas have a big year. During the summer, the males, which cannot sting, form “leks.” A lek is when males congregate to struggle for dominance and females arrive to mate – usually with the winners.

Chuck Holliday, an emeritus professor of biology at Lafayette College in Pennsylvania, has studied cicada killers extensively. He says that when they are on a lek, male cicada killers will chase anything that in any possible way could be a female cicada killer. Pretty much anything that moves.

“They will chase small birds, people and even small stones thrown in front of them. After all, for them, it’s ‘mate in the next 1-2 weeks or die childless.'”

European hornet

European hornet

My first thought was that maybe it was male cicada killers that chased the doves. But Professor Holliday pointed out that cicada killers in Wisconsin (which would be Sphecius speciosus) would be done mating around the middle of August. So since you made your observations in September, that pretty much rules out cicada killers. He suggested that chaser would be more likely to be European hornets (Vespa crabro), another large wasp (up to 2.4 cm for workers, 3.5 for queens). They look a bit like oversized yellow jackets. European hornets build nests in tree holes, and will sting to defend the nest. If a bird were to inadvertently fly near a European hornet nest, it will probably get chased. There have been reports of European hornets killing small birds such as hummingbirds. And Dr. Holliday suggests a hornet might even be hoping to take a bite out of a dove. “Hornets (including yellow jackets) will land on carcasses and even people and bite out a chunk of skin to take back to the grubs in their nests to feed them.”

So it seems more likely that it was a European hornet than a cicada or a cicada killer, and the connection with cicadas may be nothing more than that cicadas and European hornets are both associated with trees. But if you see it again, look to see if it’s a large hornet. If it’s a cicada killer, from a distance it will look mostly black with some red, whereas the European hornet will show yellow, like a large bee or yellow jacket.

Cite this article as: Pelletier, TC. (September 19, 2014). What is chasing these birds? Retrieved from http://askanaturalist.com/what-is-chasing-these-birds/ on December 21, 2014.

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