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hello,

one of my ferocactus herrerae has little drops of thick, mostly-transparent pus forming around some of its areoles. can anybody advise me of what might be wrong with it and how i can remedy it? i've been watering it quite generously every two weeks across the summer (as I read they are big drinkers). worried i might have over-watered and it's starting to rot?

Taste it. If it is sweet then it is just honeydew which the plant naturally exudes to attract more insects.

Could it be something like guttation? Although they're not cacti, my pothos plants do that.
http://en.wikipedia.org/wiki/Guttation" onclick="window.open(this.href);return false;

A lot of Ferocactus species produce this liquid. It is natural and completely harmless to the plant - but it is a bit unsightly. You can remove it with a cotton bud dipped in water.