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.
Previously on “string of bright green 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 ….
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.
Previously on “string of bright green 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.
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.
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.
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.
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.
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 …
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.
The First String of Green: In July, I received an email and photo from Emily from Nova Scotia:
“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.
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:
“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 …
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?