Life in a Pond: Underwater Predators

Eastern Newt

On Saturday June 6th I spent some time at the Beaver Trail, mostly looking for birds and dragonflies. There weren’t as many odes flying as I had hoped, but I did catch both Spiny and Beaverpond Baskettails, and found a Belted Whiteface at the boardwalk. Taiga Bluets have emerged, and a Fragile Forktail at the boardwalk was my first of the year. I only found 23 species of birds, with both warblers and flycatchers well-represented; species included Eastern Wood-Pewee, Alder Flycatcher, Eastern Phoebe, Great Crested Flycatcher, Eastern Kingbird, Black-and-white Warbler, Common Yellowthroat, Yellow Warbler, Chestnut-sided Warbler (seen), and Black-throated Green Warbler. The only other species worth noting are Purple Finch and Virginia Rail.

I spent most of my visit at the V-shaped boardwalk watching for odes, but quickly became captivated by the creatures lurking just below the water’s surface. It all started when I saw what looked like a salamander swimming just below the surface. I abandoned my search for odes and began watching the salamander instead. After taking a few photos and checking my ORAA (Ontario Reptile and Amphibian Atlas) app I realized it was an Eastern Newt. I have only photographed this species in its terrestrial form, both times in Marlborough Forest – I have never seen one in the water before.

Eastern Newt

While some species of newts transform directly from aquatic larvae to aquatic adults, others transform from the aquatic larval stage to a terrestrial form before maturing into aquatic adults. Newts in the terrestrial stage are called efts. There are two subspecies of Eastern Newt in Ontario: the Central Newt, found in Northwestern Ontario, and the Red-spotted Newt, found mainly south of Highway 101 (the highway that runs between Timmins and Wawa). Both the Red-spotted Newt adults and efts have two rows of dark-ringed red spots along their backs which distinguish them from all other Ontario salamanders.

Red Eft (Marlborough Forest, 2012)

I spent about half an hour watching it swim to the surface, where it seemed to pick off floating bits of food, and diving beneath floating cattail stems and other sticks and pieces of vegetation in the water. Then I realized there were two newts present – while they didn’t seem to interact much with each other, it was neat to see them going about their lives in the shallow water below the boardwalk.

Eastern Newt

Eastern Newt

The more I watched, the more I realized there were other creatures in the water with them. Some I noticed right away due to their size, such as this tadpole (species unknown).

Eastern Newt with tadpole

This one I noticed when I saw all the legs – it looked like a stick insect of some sort, but when I got home and uploaded it to iNaturalist it suggested a water scorpion (Renatra sp.), a type of insect I’d never even heard of before!

Eastern Newt with Water scorpion

Commonly found in vegetated ponds consisting of fresh or brackish water, these long-legged ambush predators spend most of their time in the water waiting for prey. Water scorpions eat a variety of creatures including Daphnia, small tadpoles, fish, backswimmers, and mosquito larvae, using their long specialized front legs to grab them. Water scorpions do not sting, and are harmless to humans. What looks like a long tail or stinger is actually a snorkel that consists of two half cylinders which delivers air to its spiracles, or breathing holes, on the abdomen. In the picture above it looks as though the “snorkel” is protruding above the water’s surface, allowing the creature to breathe.

Water scorpion

Then something larger swam into view, and at first I had trouble discerning what I was looking at. Then I realized it was a tadpole of some sort in the grip of something else – a predator that looked like nothing I’d ever seen before. It looked vaguely shrimp-like, so I spent some time googling predators of tadpoles and came up with this gruesomely-titled scientific article: “Diving Beetle Adults and Larvae Dismember, Eat Tadpoles“. There were no pictures of the larvae in the article, but when I googled “diving beetle larvae” it seemed clear that it was the larvae of a predaceous diving beetle of the family Dytiscidae.

Tadpole being predated by predaceous diving beetle larvae

Like dragonflies, both the adult and larval forms of the predaceous diving beetles are predators, and they often hunt prey larger than themselves. The larval form has its own name – water tiger – although the way they kill and feed more resembles the method employed by Robber Flies than tigers. They inject digestive fluids into their prey via the pincers, and when the fluid has killed its prey, the water tiger will consume the partially digested tissues and organs. Needless to say, the tadpole did not survive the encounter, and it appeared to be dead but fully intact once the water tiger was done with it.

Tadpole being predated by predaceous diving beetle larvae

The theme of my visit seemed to be underwater predators – even the newts are carnivores, feeding on slugs, worms, small invertebrates, amphibian eggs, and insects in their terrestrial form and on tadpoles, shrimp, aquatic insects, insect larvae and mollusks in their aquatic adult form. And while everyone knows that frogs are predators, eating anything they can fit in their mouths, fewer people know that tadpoles eat mosquito larvae and small insects in addition to plant material and moss.

Another predator I found was floating on the water rather than swimming beneath it. This one I recognized as a Six-spotted Fishing Spider, a smaller member of the giant Dolomedes fishing spiders seen lurking on docks, logs, and in vegetation near water. Here it is hunting by anchoring its rear legs to the reed behind it while spreading its other legs onto the water’s surface where it awaits small disturbances to signal the approach of potential prey. Such prey might include other insects, minnows, and even tadpoles (poor tadpoles – they seem to be on everyone’s menu)! I’m including the Six-spotted Fishing Spider in the category of underwater predators as this species can dive below the surface of the water when escaping predators or trying to catch food. It can stay underwater for up to an hour, crawling along plant stems and leaves while obtaining oxygen through the air trapped against its body by short, water-repellent hairs.

Six-spotted Fishing Spider

Although the Fragile Forktail is an underwater predator only in its larval form, I’m including this photo as it’s a species I see only a few times each season and I quite like it. Females oviposit in aquatic vegetation often beneath the water’s surface. It is believed that this species spends the winter in nymph form, ready to emerge once the water warms up in the spring.

Fragile Forktail

Eventually I left the boardwalk to look for other insects and birds, but returned after about 40 minutes. I was delighted to see that one of the two newts was still in the same spot, swimming closer to the surface. Eastern Newts are difficult to find in the best of times, and I was really thrilled to find two adults swimming in the beaver pond here as I wasn’t expecting to see any salamanders at all this year. It was a great outing altogether, and I saw some new species and learned a lot about the various predators that inhabit our wetlands. I know I’ll be paying more attention to the creatures lurking below the water’s surface on future outings, and hope to see some other cool bugs on my next visit!

One thought on “Life in a Pond: Underwater Predators

  1. Pingback: Dragonfly Emergence | The Pathless Wood

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