Who takes the souls of animals and what is their fate?

Allah, may
He be glorified, tells us that the Angel of death takes the souls of the
sons of Adam, as He says (interpretation of the meaning):
“Say:
“The angel of death, who is set over you, will take your souls, then you
shall be brought back to your Lord.””
[as-Sajdah 32:11]. 

With
regard to the souls of animals and birds, there is no text that speaks about
them in the Qur’an or saheeh Sunnah, as far as we know. Rather what has been
narrated concerning that is a hadeeth that is not sound (saheeh). This is a
report that was narrated by al-‘Aqeeli in ad-Du‘afa’: “The lifespan
of all animals, lice, fleas, locusts, horses and mules, all of them, cattle
and so on, their lifespans are all connected to their tasbeeh. When their
tasbeeh comes to an end, Allah takes their souls, and the Angel of death has
nothing to do with that.” Al-Albaani said in as-Silsilah ad-Da‘eefah
(4/188): It is mawdoo‘ (fabricated). 

Hence some
of the scholars said that the Angel of death is the one who takes the souls
of all creatures, whilst others said that Allah takes their souls Himself
and causes their life to cease.

See:
at-Tadhkirah by al-Qurtubi, p. 75; al-Fawaakih ad-Dawaani, 1/100 

Shaykh Ibn
‘Uthaymeen (may Allah have mercy on him) is of the view that asking about
that is unnecessary. He (may Allah have mercy on him) was asked: Is the
Angel of death appointed to take the souls of animals? 

He
replied:

What would
you think if I said that the Angel of death is or is not appointed to take
the souls of animals; what benefit is there in knowing this? Did the
Sahaabah ask the Messenger (blessings and peace of Allah be upon him) about
that, when they were more eager than others to seek knowledge, and the
Messenger was more able than others to answer, yet despite that they did not
ask? Rather Allah, may He be glorified and exalted) says (interpretation of
the meaning): “Say:
‘The angel of death, who is set over you, will take your souls, then you
shall be brought back to your Lord.’”
[as-Sajdah 32:11].
He (the Angel of death) is appointed to take the souls of the sons of Adam;
with regard to the souls of creatures other than the sons of Adam, nothing
is proven. And Allah knows best. 

But the
most important thing to say in response to this question is that man should
not go to extremes (inasking questions). The Prophet (blessings and peace of
Allah be upon him) said: “Those who go to extremes (in their words and
deeds) are doomed.” So do not ask about things in which there is no benefit.
By Allah, if there were any benefit in our knowing whether the Angel of
death takes the souls of other creatures, Allah, may He be glorified and
exalted, would have told us about it, either in the Qur’an or Sunnah, or
Allah would have caused someone to ask the Messenger about that. Hence the
Sahaabah would rejoice when a Bedouin came from the desert to ask about
something that they might feel too shy to ask the Messenger about. 

The point
is, for you and anyone else who is listening, that delving deeply into such
matters is wrong, because the Messenger said: ““Those who go to extremes (in
their words and deeds) are doomed.” And on one occasion he said: “Those who
go to extremes (in their words and deeds) are doomed, those who go to
extremes (in their words and deeds) are doomed, those who go to extremes (in
their words and deeds) are doomed”, three times. With regard to such matters
of the unseen, you should take what has been proven and leave that which has
not been mentioned… With regard to matters of the unseen, we should take
that which has been proven to us, and as for the rest, we should keep quiet
about it; if it was important for us, or if there were any interest to be
served by knowing it, Allah would have explained it. Allah, may He be
exalted, said to the Messenger (blessings and peace of Allah be upon him):

“And
We have also sent down unto you (O Muhammad SAW) the reminder and the advice
(the Quran), that you may explain clearly to men what is sent down to them”

[an-Nahl 16:44].

The
Messenger (blessings and peace of Allah be upon him) did not leave anything
that we need but he explained it to us.

End quote
from Liqa’ al-Baab al-Maftooh, 11/146 

Secondly: 

With
regard to the fate of the souls of these animals, it was narrated by ‘Abd
ar-Razzaaq in his Musannaf, by Ibn Jubayr, and by al-Bayhaqi in
al-Ba‘th from Abu Hurayrah, that he said concerning the verse
(interpretation of the meaning), “There
is not a moving (living) creature on earth, nor a bird that flies with its
two wings, but are communities like you. We have neglected nothing in the
Book, then unto their Lord they (all) shall be gathered”
[al-An‘aam 6:38]:
All creatures will be gathered on the Day of Resurrection, animals, beasts,
birds and everything. Then Allah’s justice on that day will reach such an
extent that Allah will settle the score for the hornless animal with the
horned one. Then He will say, ‘Be dust,’ at which point the disbeliever will
say: ‘Would
that I were dust!’
[an-Naba’ 78:40]. 

See:
Tafseer Ibn Katheer, 3/255 

Al-Albaani
said in as-Silsilah as-Saheehah (4/466): This was narrated by
as-Suyooti in ad-Durr al-Manthoor (6/310), but he did not say
anything about its isnaad as he usually does. According to Ibn Jareer
(30/17) it is qawiy. End quote. 

And Allah
knows best.