Bug Munching (Photos)

I've been trying to juggle my cacti & succulents around to get them the best spot to grow in. I used to have them in a sunny spot on a deck but possums kept munching them and literally yanking them out of the soil.
I moved them to another deck which receives less light, but I was worried they weren't getting enough there so I moved them down onto the concrete which receives a bit more light, and is still free from possums. However, I noticed ants crawling in the pot since it was now on the ground (and, as it looks, other bugs too).

Rrecently I've noticed this cactus going a yellowish brown colour on the edges, seems like it's being munched. I'm not sure if the roots have been nibbled yet but I'm a bit worried (check photos below).
I can re-pot this guy in a separate pot on my sunny deck if need be, since the possums don't like to touch the spiky ones.




As you can see from the second photo, the rib thingy of the cactus is folding on itself and it looks like it's collapsing, and I'm afraid there is quite a bit of damage under the soil.

I've also got an Opuntia which I had also moved down to a lower level at the same time. I thought it was rotting at first but now I think it may be victim to the same culprit as this one. I've moved it up higher and it seems to have stopped. We've also had quite a bit of rain recently so it's been fairly wet for a few days. I'm wondering whether I should cut above the dying pad and attempt to grow the top part by itself.

If it looks like it's tilting a bit, it is. I think it's about to fall over since the base is pretty damaged and doesn't really provide much support.

If ants have been in and around your cacti you may want to unpot it and check for root mealy bugs.

The yellow-brown marks on your Ferocactus? might be slight sunburn as the affected area seems to be along the tip of the ribs. Usually if some insect has taken a bite it will leave a little crater which would heal but leave an annoying scar.

Yep I agree with cactusboy, looks like sun damage/burn.

I see, thanks. I'll keep an eye on it over the next week or so. Any advice on the Opuntia?

In regards to the Opuntia I think it looks fairly healthy, nothing to stress about in my opinion anyway.
I would re-pot it in a bigger pot with the soil level a bit higher. My logic would be to promote more root growth with more areoles covered. It should also make it more stable and improve the aesthetic value too.

I've had something similar on a microdasys... I can't for the life of me figure out what it is. It's not just ageing, as the skin becomes all cracked and flakey almost like something fungal is at work. Antifungals don't seem to do anything, and systemics also have nil effect. I've examined the plants and can't seem to find any bugs at work.

On the plus side, it doesn't seem to be communicable to other plants as I am yet to see any evidence of this problem occurring on other plants kept near the effected Opuntia.

Hmm, that's odd. I'll repot this one in a few days and tell you how it goes.

my O.microdasys has that stuff too. i think its natural, haven't a clue what it is though. i wouldn't stress about it.

also you have the somewhat rarer crested/monstrose/contorted form of O.microdasys, called cv. 'Funny Bunny'. it develops wavy pads.
info:
http://www.cactus-art.biz/schede/OPUNTIA/Opuntia_microdaysis/Opuntia_microdasys_contorta/opuntia_microdasys_forma_contorta.htm