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.
Kent and Derbyshire both begin their 2019 T20 Blast campaigns with victories, beating Somerset and Yorkshire.
Derby boss Phillip Cocu says he is unfazed by taking a job outside the Premier League ahead of his first season at the Rams.
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The story of how the first moon landing was saved
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