While examining the critters of the vernal pools, we also found Caddisfly larave. The larvae of many species of Caddisfly build cases around them and the case is both species-specific and habitat specific. The one pictured below seems to have used dead plant material and arranged it lengthwise. Can you distinguish its head and thorax sticking out at the lower left end of the picture?
The first Caddisfly larvae I learned about were in a stream and had built their cases from small pebbles. Since then, I have found many other species in different watery habitats with cases built from leaves, twigs, and other organic material. Here’s one from another pond with a different arrangement of plant material:
Here is a 22 second video of the this fellow moving about. If you have your sound on, you’ll hear voices speculating about the critter’s emotions and food preferences…
I don’t think he was unhappy. I think that’s how he steers! And I don’t think he eats mosquito larvae – though I could be wrong. Most often in vernal pools I see them munching on amphibian egg masses.
While the larvae and pupae are aquatic, the adult will be airborne:
Caddisflies attach their cases to some underwater object, seal the front and back apertures against predation though still allowing water flow, and pupate within them. Once fully developed, most pupal caddisflies cut through their cases with a special pair of mandibles, swim up to the water surface, cast off skin and the now-obsolete gills and mandibles, and emerge as fully formed adults. <source>
Adults hatch synchronously making it easier to find a mate. (Fly fisherman time some of their outings to coincide with these hatches.) The adults in most species don’t eat. Here’s a particularly large species photographed by Jenn Forman Orth:
I’m pretty sure this is not the species that uses vernal pools… but the adults of most species have this same basic body shape.
I had read about them. I had seen pictures of them. I had heard mini-lecture/explanations about them. But I had never seen them with my own two eyes – alive and swimming in a vernal pool… until now! I think they might be one of the cutest things I’ve ever seen.
In this photo, the one on the bottom is definitely a female – the dark blob between her thorax and abdomen is a brood pouch containing eggs. I’m not sure about the other one. Fairy Shrimp have two sets of antennae. The second set on males should be extra long as it is used for grasping the female during mating… we can’t really see this indivdual’s other antennae. Maybe the other is also a female whose brood pouch has already been emptied? It sort of looks like there is an empty pouch there, doesn’t it?
Biologists say that Fairy Shrimp is an obligate species in vernal pools. In other words, Fairy Shrimp must breed in temporary, fishless pools that dry up in summer. Other obligate species are Wood Frogs and Mole Salamanders (Spotted, Marble, Jefferson, and Blue-spotted). If any of these species are found in a pool, it can be designated a true Vernal Pool. Vernal Pools have become a focus for many conservationists and there are many programs to locate and catalog them throughout the US. Click here to read about a Vermont Vernal Pool program, for example.
Fairy Shrimp are fresh water crustaceans that swim with 11 pairs of leaf-like legs. Here’s 8 seconds of video of the little critters swimming in a pan:
(The other dark wigglers in the pan are mosquito larvae.
Fairy Shrimp have amazing adaptations for survival, including these noted in Scott Green’s article (link below):
Though the resting period usually varies between 6 to 10 months, eggs have been hatched in a laboratory after 15 years. Eggs have been subjected to temperatures as high as 99C and as low as -190 C and remained viable.
Here are the Fairy Shrimp and mosquito larvae in their natural setting:
We visited several vernal pools last Friday and we saw one or two Fairy Shrimp in all. But one pool – the one that was shrinking most rapidly – that one was just teeming with them! It was amazing.
I’m 52 years old, and I still like to go mucking around in the ponds. I guess all those years of singing I Won’t Grow Up at Girl Scout Camp, then later in the show Peter Pan caused a self-fulfilling prophecy… Anyway, I just can’t resist going to the ponds in spring…
A bunch of us went out with Dr. Tom Erlandson to visit several ponds at the Erlandson Overlook Park (named in his honor). Seems none of us can grow up, eh?
At the first pond, we came across huge egg masses that were hatching. From the edge of the pond, the masses looked like Wood Frog eggs. We scooped some into a pan to observe.
The amphibian larvae were only about the size of a hemlock needle. (Do you also see the Caddisfly Larvae in the middle of the egg mass?) So, we went on blithely telling people that these are Wood Frog Eggs and the little guys are Wood Frog tadpoles…
But then, we looked more closely…
The gills are on the outside of the little guy’s head… But are they feathery enough to make it a salamander larva, rather than a tadpole? Still not sure… Here’s a little 30-second video in which my friend Mike encourages the little critters to swim for us:
So, what do you think? Wood Frogs? Or Salamanders?
Maybe. Probably not. How can you tell? Stick your finger in it (or a stick, if you’re squeamish).
If it immediately “heals” – that is the shiny film closes back up again – it really IS oil. If it doesn’t, it’s a naturally occuring bacteria or other natural source. According to the USGS, these kinds of films “can be found anywhere that ground water, which lacks oxygen and carries iron and manganese, discharges into a stream.” I assume ponds are likely candidates, too. The article goes on to say:
Certain bacteria, the oxidizers, fix oxygen onto iron and manganese. Other bacteria, the reducers, remove the oxygen. In fixing or removing oxygen, some are getting energy and others are performing other life functions. Bacteria have been involved in the iron and manganese cycles for billions of years.
So, don’t worry about your pond being polluted until you stick your finger in it!