Aquatic Weirdness

I have a small water feature in my garden. It's a rectangle stone vessel that's about 28cm x 15 cm and maybe 12 to 15 cm deep.  When I had the garden re-done, the gardener move the vessel, filled it half full of some mystery brownish mud, and planted water iris in it. the iris are thriving but the vessel itself is filling with these little black swimmers that are about the size of two grains of short-grain rice.  At first, I thought they might be frogs and was excited.  But I think I'm looking at the adult bugs.  And perhaps the tiny worm-like animals (they twist and turn to get around) are the larvae stage of this bug.  So far, they haven't evolved into anything else, but the population is growing. It's hard to get a good shot as they are only on the surface of the water until a shadow comes over the vessel and then they all dive to the bottom and sit on the mud.  

Any help in identifying them and letting me know if they are inert or need to be removed is welcomed.

Hi Barbara,
it is very hard to tell by your photo. Are they propelling by little spurts? Then they could be mosquito pupae.

In any case, it is both hard and not advisable to try to keep water insects from populating your little pond. They will help keep the water clear and soon form a balance. Some will eat the others, you will probably get dragonflies, and if you are lucky even amphibes.

I would not worry too much but welcome the life forms in your garden.

From your description, sounds like it might be diving beetles. They live in the mud but breathe air, which is why they need to stick their butt out of the water. They are predators (especially their larvae) so will eat other larvae (mosquito etc). The adult beetles can fly to look for another watery environment, which is probably how they got into your vessel. Sometimes they can even land on shiny surfaces thinking that it's water.
They were the first inhabitants of my pond and survived the winter in there. They didn't hurt my plants or guppies, so I guess they're harmless but they could probably bite you if you grab them with bare hand.

I would love to see a closeup of just one of these bugs.

Those might be backswimmers or water boatman:

https://en.wikipedia.org/wiki/Lesser_water_boatman

Barbara,
Your pictures are very good but the bugs are a bit small as Anne said. The photos can be enlarged.  They are two stages of mosquito water cycle, the larva and pupae.  The long thin ones are the larvae, also called wrigglers.  They have a furry butt that they breath through.  The pupae have two small horns that are the breathing part.  They are also called tumblers.  It looks like there are a number of egg beds there.  To rid your mosquitoes, you can add one drop (out of an eye dropper) of olive or other kitchen oil but way better is to put in some potted reeds and encourage dragonflies and frogs.

One thing to be aware of is that some mosquito can reproduce in wet soil, between wet leaves etc, so just emptying the water may not always be the solution to get rid of them.
More info: https://www.epa.gov/mosquitocontrol/mosquito-life-cycle

We had a new pond and quite quickly had mosquito larvae turn up. We don't mind insect life in general, but didn't want to be hosting a mosquito breeding site near the house.

We added a dozen small goldfish and the mosquito larvae cleared up in a week. I was concerned that we might impact other insect life, but we have had multiple species of dragonflies and damson flies turn up and breed successfully, as well as water snails and other things.  We don't feed the fish. They breed easily and replace themselves, despite a fairly regular heron visiting.

I would put a couple of very small goldfish or similar in there.

Maybe Whirlygig beetles? The diving behavior sounds right.

https://www.bellinghamherald.com/living/family/article137766438.html

Wow! Thanks, everyone. While I'm not a fan of mosquitoes, I don't want to do them any harm either. I like the idea of a few goldfish. I'll get a better camera see if I can get a close up. I've got some reading to do, first. Thanks for the links.

Just bear in mind that goldfish will dig in the mud and possibly upturn your plants. And they can grow huge (the more natural looking anyway, maybe there are some dwarf varieties that can't grow because of crooked spines etc). If it doesn't get too cold, guppies are great as mosquito hunters and they won't destroy your plants. You can also try medaka (Japanese rice fish) - I've seen people keep them in really small containers.

I second Flora's suggestion of smaller fish. If you're going to add them at all. That's not a lot of water and goldfish are very messy, as well as really being too large as they grow. Without at least 10 gallons per goldfish (preferably 20), you'd probably be looking at either sick or dead fish because of too high ammonia/nitrites/nitrates or having to do tons of water changes to keep it from going that way. Smaller fish would be much better for the well being of the fish and for keeping the water healthy and not causing imbalances due to too much fish poo.

Thanks for all the advice.  I will get the smaller fish as suggested by Flora Eerschay. I've had goldfish (well, I had a goldfish in a 20-gal tank, and I have one tank twice that size too), but the fish didn't survive the move to Nikko.   I'll probably have to take the fish inside for the winter, but setting up a tank again shouldn't be a problem -- I have all the equipment.  Perhaps there will be other issues with indoor/outdoor fish, but I can try.  I use the site Fishlore.com to get the info I needed for the goldfish, I'm pretty sure I can get some info on the ricefish Flora recommends.  Heck, I can probably scoop some out from one of the nearby rice paddies. Thanks also for the link to ryo Wantanabe's Youtube channel.  I'll be learning more about Medaka there too.

I also recommend you Diana Walstad's book about low-tech planted aquariums. The basic principles can be applied to garden ponds and other water features, and it's fascinating stuff!

UPDATE:

I bought a smallish indoor/outdoor fishbowl, 5 Medaka fish (2 gold, 3 silver) 3 water plants, and 1 snail.  I got a bonus tiny snail who was riding along with the water plant. Twenty-four hours later everyone and everything is still alive.

I have to love the way salespeople in Japan want to make sure you're happy with your purchases. I know I make a difficult customer because my Japanese is nowhere near the level to have a sustained conversation. Yeah, I can ask "Where is the bread?" at the supermarket, but more than half the time I end up squinting at the clerk until they dumb down the answer to baby-talk. Then I understand, but it's more intuitive than actual understanding. David Sedaris understands. https://en.wikipedia.org/wiki/Me_Talk_Pretty_One_Day

She was horrified when I showed her a photo of the outdoor water vessel that I wanted to put the fish in.  That photo threw her into a panicked, high-pitched, fast-paced diatribe while she showed me every available fish bowl in the department.  I caved, and bought one, bringing my total number of fish bowls and tanks up to 5, I think. The poor woman ran around the pet department, making sure I had a water treatment solution (I do and I used it but I don't think I needed it), a bubbler (I have several, and two air pumps), and food for the critters (not specifically for Medaka, but I have lots of goldfish food - flakes and pellets - but I bought the smallest container of Medaka fish pellets available) and plants where they could hide.

I haven't set up a tank since I moved 18 months ago, so I have no aquatic plants. I picked out a few, which she gently plucked from my hands while muttering to herself, put them back in the trays, and redirected my attention to water hyacinth.   I think she thought the fish would die without treating the water first, but they're fine with tap water at the same temp as the bags and a scant hour of treating the water while the fish hung out in their open bags in the bowl. I live very close to the water treatment plant and 2400 feet up the mountain. I tested the water with a Zero Water gauge a couple of months ago and it read ah, zero. Perhaps it wasn't a bad idea to get them acclimated in the bowl, then put the bowl in the outdoor water feature (I have to find a better term for that 100-year-old rectangular stone box). I also need to shade the box so the fish don't boil and no, an umbrella will not do.  In the meantime, everyone in the bowl seems happy. The snail (the roundish blob in the photo) has escaped the bowl twice now, but the sales lady warned me that that would happen so I know to look for her/him. S/he's made it all the way to the outside base of the bowl - the farthest s/he's crawled away so far.

The mosquito larvae and bugs are doing fine, by the way.

Flora Eerschay wrote:
I also recommend you Diana Walstad's book about low-tech planted aquariums. The basic principles can be applied to garden ponds and other water features, and it's fascinating stuff!

Flora, Is it this one? https://www.amazon.com/Ecology-Planted-Aquarium-Diana-Walstad/dp/0967377366#:~:text=In%201999%2C%20Ms.,now%20into%20its%203rd%20Edition.  Ecology of the Planted Aquarium: A Practical Manual and Scientific Treatise for the Home Aquarist

Anne Miller wrote:I would love to see a closeup of just one of these bugs.

Those might be backswimmers or water boatman:

https://en.wikipedia.org/wiki/Lesser_water_boatman

Water boatman of some type was my guess too. When they swim around it kinda looks like they're rowing a boat but they can go much faster than I can row a boat LOL

Barbara Manning wrote:Wow! Thanks, everyone. While I'm not a fan of mosquitoes, I don't want to do them any harm either. I like the idea of a few goldfish. I'll get a better camera see if I can get a close up. I've got some reading to do, first. Thanks for the links.

So, I am curious what those swimmers turned out to be?

Mosquito larva or something else?

Hello all,

It's been a while since I posted. Life got in the way and I was AFK for quite a while. For those who are interested, let me catch you up.

My Medakas did not survive captivity much less the ravages of the outdoor cistern.  It's been maybe 3 or 4 years since I hosted goldfish and that was in Tokyo. Now I live in Nikko where the weather is vastly different, and even though the water tests are "better than in Tokyo" maybe I did something wrong.  Anyway, the poor fish did not survive more than 6 months inside, but the snails hiding in the aquatic plants I bought were incredibly prolific.  https://www.aquasabi.com/aquascaping-wiki_parasites_a-plague-of-snails

I found myself removing egg sacs almost daily. I knew better than to toss them in the sink or toilet, but it still bothered me.  Late last week, I took the small amount of water and aquatic plants out to the cistern and poured it all in.  I figured the snails might have a chance to eat all the sludge and those that crawled out of the vessel would not live in the garden. It's rained almost every day since then, but once the weather turns, I'll let you know if the snails lived or died.

In the meantime, I've decided that the cistern is not a good home for aquatic plants like Iris that need a seasonal change of wet and dry environments. I have to figure out some other way to manage this vessel.