My favorite this week is also my first observation of the year. As I was getting dinner ready, I discovered that my block of cheddar had been colonized:
This lifer is also relevant to two other current threads:
Would mold growing on my food be cultivated? - General - iNaturalist Community Forum
House of a thousand species - Nature Talk - iNaturalist Community Forum
My first thought was Penicillium because of the flat, white colony that turns blue in the center. I did a web search for “species of mold on cheddar” – I had to be specific like that because just searching “mold on cheese” returned articles about blue cheese, or about spoilage in general. As it turns out, there are a surprising number of articles about the species of mold on cheddar. On the whole, they agree that Penicillium commune is the one that usually infects cheddar.
This makes sense, because the Wikipedia article on P. commune says that it is considered to be the wild ancestor of Penicillium camemberti, which is cultivated in the making of camembert and several other cheeses.
That same Wikipedia article also said that, although this species does not produce penicillin, it has shown antibacterial action against two particularly nasty hospital-dwelling germs, Pseudomonas aeruginosa and Staphylococcus aureus. You can learn fascinating things when you get past our culturally ingrained squeamishness.