If killing these would only require a small action on the part of the person in salah, then there is no harm in doing it. Abu Hurairah reported that the Prophet sallallahu alehi wasallam said: "Kill the snake and the scorpion during the salah." This is related by Ahmad, at-Tirmidhi, Abu Dawud, an-Nasa'i, and Ibn Majah. The hadith is hasan sahih.
'Aishah said: "The Messenger of Allah was offering salah in the house and the door was locked. I came and knocked on the door and he walked over to open it for me and then he returned to his place of prayer. The door was in the direction of the qiblah." This is related by Ahmad, Abu Dawud, an-Nasa'i, and atTirmidhi. The latter calls it hasan. It may be observed that in this hadith, he did not turn away from the qiblah either in opening the door, or in returning to his place. This is supported by what has been related that the Prophet would pray and if anyone knocked on the door, he would open the door provided the door was in the direction of the qiblah or on his right or on his left, but he would not turn his back to the qiblah. This is related by ad-Daraqutni.
Al-Azraq ibn Qais relates: "Abu Barzah Al-Aslami was at al-Ahwas, at the bank of a river, and he prayed while holding the reins of his horse. The horse started going back, and he (i.e.Abu Barzah) followed the horse. A man from the Khawarij said: 'O Allah, be rough on this man, see how he is doing his prayer.' When Abu Barzah finished his prayer, he said: 'I heard your statement. Certainly, I participated in six or seven or eight battles with the Prophet, and I am certainly aware of his leniency. Certainly, I would rather restrain my animal than let him run off loose as that would have caused me a great deal of trouble.' It was 'Asr prayer that Abu Barzah offered, and he prayed two rak'at." This is related by Ahmad, al-Bukhari, and al-Baihaqi.
Concerning taking a lot of steps, Ibn Hajr says in Fath al-Bari: "The jurists are agreed that taking many steps invalidates an obligatory prayer. They interpret the hadith of Abu Barzah as referring to taking just a few steps."