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Other Creatures Underwater

Fairy shrimp are some of the many crustaceans that can be found in an ephemeral wetland -- a wetland that doesn't hold water all year and so has no fish to prey upon them. These fascinating little creatures can lay eggs that will hatch right away and eggs that are more heavily protected and will remain dormant in the soil through dry spells waiting for there to be water in order to repopulate the wetland after it has been dry. (These eggs can also pass through the digestive system of ducks and other waterfowl and thus populate other wetlands as well.) Fairy shrimp can be active during the winter under the ice after hatching with fall and winter precipitation!

This is a freshwater isopod making its way across the floor of the wetland pond. Like fairy shrimp, isopods are crustaceans. If it looks similar to the "roll'em up bugs" (aka sow bugs, pill bugs or woodlice) you may see around your garden, under rocks, etc. That's because those are also isopods. About half of the world's 10,000 species of isopods live on land, making them the most successful land-dwelling crustaceans. Interestingly, the land-dwelling isopods still breathe through gills and so are restricted to humid and damp environments. Of the remaining 5000 species of isopods, the majority live in the world's oceans, but about 500 species are found in freshwater. The one pictured above was less than an inch long, but the largest species, which can be found in the deep sea, can be up to twenty inches long!
This is a disintegrated diving beetle, so-named for the broken lines on each side of its back. It is one of some 600 predaceous diving beetle species found in North America. Visible in the photo are the hairs on its hind legs which make them more effective for swimming and a bubble at its back end, which it carries underwater for oxygen. Scientists have found that insects that carry air with them underwater not only benefit from the oxygen stored in the bubble itself, but that as that oxygen is used up by the insect's breathing, it is replenished by dissolved oxygen in the water moving into the bubble to take its place. Scuba tanks can't do that! This process does not go on indefinitely-- the beetle eventually has to return to the surface to get a fresh bubble. Still quite amazing.
Another species of predaceous diving beetle found in the wetland. As the family name "predaceous diving beetle" suggests, these beetles are aquatic predators.
The giant water scavenger beetle, at about one and a half inches in length, is the largest species of aquatic beetle found in the United States. The silvery areas on its underside are where it has short hairs that help to trap air bubbles for breathing underwater and again the feathery-looking legs facilitate efficient swimming. Adult aquatic beetles, including the predaceous diving beetles pictured above, are able to fly and can move between bodies of water or, in the case of an ephemeral wetland, find another body of water when the one they're in dries up.
Giant water bugs are true bugs. Although we commonly use the word "bug" to refer to anything with six legs (or maybe even anything "creepy crawly"), true bugs are a specific order of insects with their own characteristics. One of the characteristics of the true bugs is a hypodermic needle-like mouthpart through which digestive juices are injected and then liquified meals sipped. Some of the true bugs, such as cicadas and aphids, use this needle-like mouth to suck juices out of plants. Others, such as the giant water bugs, are predators that capture prey, inject digestive juices that liquify their prey's insides and then drink that. They do not prey on humans but can inflict a painful bite. Like the aquatic beetles, adult giant water bugs are capable of flight, but not this one at this time. This is a male giant water bug and his mate has glued her eggs to his wings. He's in charge of childcare until the eggs hatch. During my observation of this one he repeatedly passed his long hind legs over the eggs apparently cleaning them. You can see that the eggs in the center of his back, which he may not be able to reach, have a lot more organic material accumulated on them.
The water boatman (left) and the backswimmer (right) are two more aquatic true bugs. Both feature long back legs that function like oars on a rowboat. As with other true bugs, both have piercing and sucking mouthparts. The water boatman lives on plant juices while the backswimmer preys on other creatures just as the giant water bugs do. As you can see, the backswimmer comes by its name honestly, swimming on its back. Both carry air bubbles with them when swimming underwater, and they can also fly to other wetlands when needed; thus, they can show up in your backyard pool, for example.
Not to be outdone by the insects, there are also aquatic spiders. This is a six-spotted fishing spider and it can catch prey both above and below the surface of the water. In this photo it dove quickly under a leaf on the water's surface when I approached, giving me the opportunity to get this underwater portrait. Like the beetles and bugs pictured above, fishing spiders carry air bubbles underwater with them as an oxygen supply.
This ramshorn snail is making its way across the underside of the water's surface! Snails are abundant in the wetland and eat algae and decaying matter. They survive the dry periods of the wetland by burrowing into the mud and secreting a mucous covering over the opening of their shells to keep from drying out. Despite their shells they end up being a prey item for many of the other creatures in the wetland.
This is a water scorpion -- another true bug but quite unlike the giant water bug in appearance. Nevertheless, it has similar front legs designed for grabbing prey and an obvious sharp hypodermic needle-like mouth for injecting prey with digestive juices and sucking out the contents. Many note the similarities between the water scorpion and preying mantises. They are not related but obviously have some similarities in the elongated bodies and front legs perfect for grabbing prey. The long appendage at the water scorpion's backend is called a syphon and functions like a snorkel, reaching the water's surface to enable it to breathe air while underwater. Like the aquatic beetles, the giant water bug and the water boatman and backswimmer, this creature can also fly if needed to move between wetlands.
These are mosquito larvae hanging out at the surface of the water. Like the water scorpion, they use syphons just above the water's surface to provide them with oxygen from the air. When disturbed they close off the opening of the syphon and through a series of rapid wriggling motions escape to the bottom of the pond only to resurface later again with a series of wriggling motions, resulting in the common name for this stage of their lives: "wrigglers."

Related Video

  • Fairy Shrimp Swimming -- a 19-second video showing the unique swimming motion of a fairy shrimp
  • Swimming Insects -- 20 seconds underwater featuring a diving beetle making a quick trip to the surface to replenish its air supply followed by a backswimmer darting around, running into the camera, replenishing its air supply and finally docking on a nearby plant stem. Several other backswimmers can also be seen.

Related Website

The Homer Lake Wetland Blog features posts on most of these creatures along with others not mentioned here.

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Credits:

Text, Video and Photos by Doug Mills