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He wrote: "The problem is that animals such as snakes, spiders, crocodiles, rats and many invertebrates are already misunderstood and thus unfortunately vilified, despite the incredibly important roles they play in the world's ecosystems and our lives.
"By orchestrating a fear of them among your contestants, I'm afraid you're reinforcing and exaggerating a terrible ignorance and intolerance of these remarkable animals."
Packham also dismissed claims that none of the animals featured in the show are harmed in any way.
"I can guarantee that some animals are harmed during production, because they are fragile or easily stressed. Or simply killed, as they are in your bushtucker trials."
He added: "The show has been running for years now. Surely it's time for it to mature, for you to accept that, as pillars of the British broadcasting community, you should put an end to this inhumane, embarrassing and destructive aspect of an otherwise great show."
Animal welfare charity, PETA, echoed Chris's thoughts in a statement to HuffPost UK, saying: "Unlike the celebrity contestants who volunteer to be on the show, animals are not there by choice and deserve more than to be used in stressful and cruel situations in a desperate attempt to boost ratings.
"Packham is absolutely right to assert that – like the PETA motto says – animals are not ours to use for entertainment. All animals – not just the ones that are considered to be cute and cuddly – want to live free from harm.
"I'm a Celebrity's lack of kindness is matched only by the show's total dearth of creativity, evidenced by the fact that it has repeated the same irresponsible and inhumane tasks for more than a decade.
Meanwhile, ITV have issued a response to Chris Packham's letter, saying: "Ant and Dec are the presenters of the show, and as such are not involved with the formatting of the trials, which are devised by the show's producers.
"ITV takes animal welfare very seriously and expert handlers are on hand at all times."
ITV was fined in 2010, after contestants Gino D'Acampo and Stuart Manning killed and cooked a rat on the show.
The RSPCA in New South Wales, Australia said it was not acceptable that an animal had been killed for entertainment.
Gino and Stuart were originally charged with animal cruelty, but the charges were dropped after ITV admitted responsibility.