Locusts are a collection of certain species of short-horned grasshoppers in the family Acrididae that have a swarming phase. These insects are usually solitary, but under certain circumstances they become more abundant and change their behaviour and habits, becoming gregarious. No taxonomic distinction is made between locust and grasshopper species; the basis for the definition is whether a species forms swarms under intermittently suitable conditions.
It is not true to say that every locust is Halal to eat. Locusts which die in the water or on the earth are not Halal at all. The Hadeeth from Ali Ibn Jafar, the brother of Imam Musa Ibn Jafar (AS): I asked Abul Hasan (AS) (Imam Musa Ibn Jafar): About the locusts found dead in the water or in the desert, can it be eaten? Imam said: Do not eat it. (Wasaa'il Al-Shia, Hadeeth number 30067).
Only locusts which are taken alive then die are Halal (Hadeeth number 30068 in Wasaa'il Al-Shia).
The people in Arabia used to eat all types of locusts and many of them still eat it, but Islam forbade eating the dead locusts and the small locusts as well till it Fly.
Usually, non Arab Muslims do not eat and even do not like the idea of eating locusts, while many Arabs specially those wo live in the desert, do.
It is not necessary for the Imam (AS) himself to eat every thing which is allowed to eat or to do every thing which allowed to do. Imam (AS) is the Best and Most humble servant of Allah (SWT) and he does only the best deeds and not every deed which is allowed for general public who have their their own needs and circumstances.
Yes but with conditions. It becomes Halal if you catch it or if it has been caught by a Muslim. It is not allowed to eat it if it died before catching it. Small locusts which can not fly are not allowed.
This is mentioned in many books of Shia and Sunni scholars.
It is mentioned in Saheeh Bukhari , Hadeeth number 5176 narrated from Ibn Abi Awfa. Same Hadeeth is also mentioned in Saheeh Muslim, Hadeeth number 1952.