Wildlife experts say the Derbyshire haven is the best place in the country to see the Wall butterfly.
Phillip Allen was taken to hospital with head injuries on 27 June and died on Wednesday.
The app guides users through a urine test and allows the results to be analysed online by a pharmacist.
In the postcard, the author and poet described Shirebrook as "a most hideous place".
Popular trails have been blocked with rocks and had branches placed at head height.
British swimmer Adam Peaty breaks the 100m breaststroke world record with a time of 56.88, becoming the first man to break 57 seconds.
Kent and Derbyshire both begin their 2019 T20 Blast campaigns with victories, beating Somerset and Yorkshire.
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