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 “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.
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!
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.
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.
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.