Assalamu 'alaykum wa rahmatullah wa barakatuhu Honourable Mufti, I pray you are well.
I have a question about snakes and killing them. I know there is a Hadith that tells us to kill snakes. Specifically, are the snakes cited in the Hadith dangerous snakes only or all snakes in general? For example, here where I live, there are various species of snakes in the countryside and in the streams, they are harmless snakes, not poisonous, and many of them are useful for agriculture since they eat a lot of mice, rats, insects etc.
Should these snakes also be killed?
بسم الله الرحمن الرحيم
In the Name of Allah, The Most Gracious, The Most-Merciful
In various hadith we see that the Prophet (pbuh) encourages killing snakes, especially in salah.
"Allah's Messenger (S) ordered killing the two black things in Salat; the snake and the scorpion."
In another hadith we see the Prophet (pbuh) also ordered killing certain types of snakes.
“Do not kill snakes except the short-tailed or mutilated-tailed snake with two white lines on its back, for it causes abortion and makes one blind. So kill it.”
In Raddul Muhtaar, it is mentioned that there is no dislike in killing snakes if harm was feared. 
Therefore, there is no harm in leaving these snakes if you are sure that they are not harmful to you or those around you.
Only Allah knows best
Written by Alimah Nasima Umm Hamza
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Jaami at-Tirmidhi, Hadith Number 390
 Sahih Bukhari, Hadith Number 3311
 Raddul Muhtaar, Volume 1, Page 650