Little Critters

Little Critters

late July 2013

I want to find out what is going on in the mud and water, so I bring one of my hand-made tools:  a handled kitchen sieve attached to an old broom handle with (none other than) duct tape.  I, as a relatively large animal, create bioturbation by scooping this “net” through the mud and water.  I try to create as little disturbance as I can, but I can't help stirring up clouds of tiny clay particles.

So, what am I able to find in the pond in late July?

Tadpoles!  Many of them.  But, whereas during the last visit there were teeming masses, wiggling about, feeding on phytoplankton-covered debris and swimming around, this time they are rather quiet.  I don't see many of them, but when I poke at the mud in the shallow (or, “bioturb” it), I stir up lots of them, suddenly wiggling in a panic like many people rudely awakened.

I do not yet know what kind of tadpoles these are, but I will check their development now and then.

Here, the eyes and tail are obvious.  Leg formation is still well into its little future.

Here is the underside of the same tadpole.  It is rather clear, and you can see its intestines!  Aquatic animals that feed on plant material tend to have longer intestinal tracts for the size of their bodies than “meat-eaters” do.  It's more work to digest the plant material, and they must eat a lot of it.  When this tadpole becomes a non-vegetarian frog, one of the big changes it will go through (besides developing limbs and lungs) will be a shorter intestinal tract.  And that tail will be gone, of course.

I find this critter moving in the mud toward the water's edge.  I would likely not see it but for the movement catching my eye – it blends in so well.  It's a bug, and by that I mean it's a “true bug”, in the order Hemiptera, in the Class Insecta.  It can live on land for awhile, but also in water.  Look at the back end of it (the right side, in the photo) – there is a protuberance.  That is a sort of siphon that acts as a “snorkel”.  While under water, it can stick this up through the water surface and take in a supply of oxygen from the air, then go down into the water awhile longer, hanging onto plants or debris, or on the mud, waiting for prey to pass by. 

Now, look at those two large things by the head (left). This is a modified, enlarged pair of legs that bend like an arm with an elbow so this bug can reach out quickly (or even above its head) to snatch lunch.  The combination of these predatory legs and the point at the back (which will get longer) resembles, a bit, a scorpion, which is why it's been named Water Scorpion.

This critter I see moving about at the pond surface, though I don't see the top side of it when it is doing so.  It is another “true bug”, or Hemipteran (the triangular area between the head area and wings is a clue for this group), and it swims on its back.  It is, of course, called a Backswimmer.

All insects have three pairs of legs.  In the Water Scorpion, the first pair is enlarged and modified into predatory “arms” for reaching and snatching.  In the Backswimmer, it is the third pair of legs that are modified and enlarged, this time as “oars”. These “oars” are capable of a wide range of motion.

Now you can see how the Backswimmer looks in its normal position, the way it is accustomed to moving.  It's easy to see the first two pairs of legs, looking somewhat insignificant and, in contrast, the great sweeping third-pair oars. 

In both photos, you can see the eyes at the side of the head, wrapped around from front to back.  This allows the Backswimmer to see above, below and to the sides.  

I spot these as dark dots on the bottom and floating in the water. These Pond Snails need a closer look.  When you set a snail so that its point is upward and the opening in the shell is toward you, it becomes clear whether it is a Prosobranch for a Pulmonate snail.  This one is Pulmonate.  The way to tell is this:  when held this way, the opening of a Pulmonate snail shell is on the left, and it does not close off its shell.  If it were a Prosobranch, the opening would be on the right, and it would have an operculum – in other words, it has something to close off the shell opening and protect the soft body inside.  And, it would “breathe” by extracting oxygen from water moving over a gill.

But, this is a Pulmonate Pond Snail.  It breathes by coming to the surface and taking oxygen from the air to circulate through the dense vascular system in its cavity.  This works like a lung.  The snail can then go back into the water for a time.  This explains why I see these dark spots floating up and down in the water.  Because they can go to the surface for air, these kinds of snails can live in water of lower quality. 

In this photo, you can see the mucous-covered “foot” coming out of the shell to get a grip on the new surface, which is my hand.

These snails may be eaten by crawdads, which crush them, or by tiny aquatic animals that enter its shell.

Here, the pulmonate Pond Snail's head and part of its body are coming out to explore and sense where it is.  Unlike land snails, we don't see obvious eye stalks and antennae.  It pretty much looks like a blob.

There has been plenty of worm activity at the edge, as evidenced by many trails criss-crossing in the mud.

Other things brought forth from the pond were so tiny that they will have to be viewed later under microscopes. 

 That will be for another day.