It looks like a species of lichen to me but I have never seen lichen growing on commercially available orchids before. How fast does it grow?

I don't think it's a lichen because it has almost no dimension to it plus it's water soluble (if you scrub it a bit). I washed it off again yesterday, we'll see if it comes back a third time. There's no new stuff so far. I thought it might be some orchid sap but that would be a weird color and it's not sticky or anything. I'm just stumped on that one. As long as it doesn't hurt anything I'm not too concerned.

First of all, I would like to say that from what I can see in your pics, your terrarium is very nice! You must have to work pretty hard to controll that duckweed though. =)

Second, that white stuff doesn't look like any bug or disease I've ever seen or read about, and it does look organic, so I wouldn't worry about it. Removing it is probably the best thing to do. I don't think it's a lichen, because they grow VERY slowly, but it could be some kind of fungus or mold. These things happen a lot in terrariums, as I'm sure you know. You could also try posting this on the orchids forum. I'd just keep an eye on it though. If it begins to spread rampantly and seems to do some damage, then I'd be worried. But for now it seems rather benign.

I would say mealybug, but it doesn't look like it. White scale, maybe? I am really quite stumped myself. I wonder if perhaps you could take it to a local lab and have it tested?

From what I can tell I don't think it's mealy bug or white scale either. So far it didn't come back yet but appeared on a few other spots. Mainly the cork background. I've increased the fan cycles and started misting a bit more sparingly to avoid mold or rotting. Plus, I got boatloads of fungus gnats. I've seen the posts about all the critters that show up in terrariums but I'm not too thrilled with the bugs. I can't seem to shake the slugs one of which attacked my Macodes Petola. I do have four nepenthes and four tropical sundews but especially the latter are completely overloaded, pretty much overfed ;p I got some dart frogs today and can't wait until they get a bit bigger so I can put them into the big terrarium. I hope they will take care of some of the bug problems. I highly recommend the frogs from Patrick Nabors (Saurian Enterprises, saurian.net). I bought three Dendrobates Auratus "Blue" from him and they arrived in great shape and have beautiful patterns. I know that was a bit off topic but I thought I'd throw it in ;p

Oh and sahoyaref, the terrarium is only a couple of months old. I'm about to do some remodeling of the water feature that you could see in the picture. I'm adding a filter and a better waterfall cause a lot of algae is growing in that stagant water. I have no idea how the duckweed got in there either, it just showed up one day like all the bugs. It will have to go when make the changes. It's amazing what starts to show up even in a sealed terrarium. I'm waiting for some birds and monkeys to pop up one day..lol

You do realize that you will need to culture fruit flies for your frogs to eat, right? You can't just let them eat the few bugs they can catch in your terrarium. Forgive me if you already know all this, but it really pisses me off when people get pets because they look cool or cute, and then they have no idea how to properly care for them and they die. Especially PDFs, which are endangered in the wild.

As for your slug(s), try to deal with them before you add your PDFs (unless they eat slugs, I don't know). Try the natural slug-killing pellets or a beer trap. And you probably want to remove the duck weed NOW. Believe me, it will take a lot of removal before you've got it all.

Maybe slime mold?

Here is a link that might be useful: slime mold

Hmm, slime mold. It doesn't quite look like the ones on that website but there seem to be so many forms that I don't quite want to rule it out. Especially the "acellular mass" part sounds the closest so far. The stuff I washed off the orchid didn't come back after 3 days now. There are only small patches (maybe index finger nail size) and they seem to stop to increase unlike the rather rapidly growing slime molds. But who knows.

And sahoy, of course I know how to take care of dart frogs. You'd have to be really ignorant to buy these frogs and not know how to feed them, especially considering how much trouble it is to get some. But they should still help out with some of the unwanted bugs besides the feeding and they most likely will eat young slugs (mine are pretty small) once they get a big bigger. Natural pesticides so to speak (they eat pretty much anything that's small enough and moves). I tried all kinds of other stuff including the beer thing and slug bait. It was useless. However, I found an interesting side effect. The originally dried sphaghnum moss came back to live after about 2 weeks (versus about 2 months without) where the slug pellets lied around. They seem to function as moss power fertilizer.

Interesting! I will have to try that, because I'd really love to have some live sphagnum.

Were the pellets 'iron chelate' based? That would make sense as iron chelate is an algal fertiliser. Here is an interesting article on iron's effects on sea algae.

That's what I figured, probably some iron component, although the Ortho Slug Bait I'm using is based on metaldehyde, which is basically a cyclic ether derivative. But who knows what the other 95% is. There's no specific information on it. I searched the patent database but couldn't find anything on slug repellants by the Scotts Company. That's probably cause this stuff is so old and can be formulated at will now. Most likely they added some metal chelates, such as an iron chelate or maybe iron phosphate like in Sluggo's product.

Any idea what the attractant is? Perhaps it is something simple like cereal, in which case maybe you can rejuvenate SM with cold porridge :) Or Vegemite...

"Ortho Slug Bait I'm using is based on metaldehyde"
hoschi,
Are you certain the metaldehyde won't harm the pdf's? I don't know how fast that stuff breaks down nor how sensitive amphibs might be to it.

Oh btw, slime mold was the first thing that came to mind for me too upon viewing your pics.

Nice looking terr! What size is it?

Paul,
the slug bait should be ok for the PDF's as long as they don't eat it (which is more than unlikely). However, that's not even an issue because my frogs are not in that terrarium right now. There will be at least 2 months between the application of slug bait and putting in the frogs. And that stuff breaks down in about 4 weeks. So it's all good.

The terrarium is a 75 gal. tank. I'm about to make some major modifications to the water feature. I may put up some pics once everything's done in a couple of months.

The frogs wouldn't need to eat the slug pellets in order to be harmed by them, because frogs absorb things (like chemicals) through their skin. Any residue in your tank could harm the frogs. I would 'rinse' the tank, if possible, before adding the frogs. You could flood it with fresh RO water, and then siphon out the excess water. My tank did this all by itself while I was on vacation (automatic misting system). =) Frogs are very sensitive to chemicals, so I wouldn't take any chances. I got what water I could out with an aquarium siphon, and then just held a glass under my waterfall for the rest, emptying it as the glass filled. After about 1/2 hr., the water level is back to normal. =)

I realize that frogs can absorb "chemicals" through their skin. But that's still not the same as digesting it. "Rinsing" the tank wouldn't work because I have no fake bottom. Plus, those organic compounds are not water soluble, so it wouldn't do anything in the first place. And I'm sure you wouldn't recommend rinsing my tank with nail polish, would you ;p Like I said, it's not an issue because metaldehyde is an ether and thus not very stable. Decomposition products will be washed out long before I add my frogs. I'm a chemist, I know what I'm doing.

hoschi: rinsing with acetone could be a good way to sterilise the tank completely ;)

LOL Nathan! =) Salt or vinegar would also do a good job of sterilizing! =)