If I remember correctly it's thanks to showing the picture to the doctor, which had it sent to a zoo (!), that they realized how dangerous it was and thankfully another zoo (?) had the serum.
My memory is fussy but it happened, in the UK.
Turns out the spider traveled all the way from Brazil into... Bananas.
Another common name for the brazilian wandering spider is the "banana spider" : )
Too lazy too google it so I posted what I remember ; )