I saw a opossum (the North American kind) on a golf course the other day. It looked pretty dead - there was foam coming out of its mouth and flies buzzing all around it. However, I know opossums can convincingly play dead by involuntarily entering a catatonic-like state. Are there any tell-tale signs indicating a opossum is really dead? Would the flies be buzzing around it if it was actually alive?
How to tell if an opossum is truly dead?
The only safe thing you can do is wait. Commonly after an hour, the ears of the Opossum start to move slightly. This is your indicator to know that it's an actor :)
After four hours of stiff ears, you can be pretty sure that you are looking down on a dead animal. Call the competent authority (local veterinarian, wildlife rehabilitator, animal control etc.) for assistance.
From Wildlife Rescue Rehab:
Give a "dead" opossum the benefit of the doubt before disposing of the body. It may be "playing possum" as an involuntary response to a threat, in which the opossum becomes comatose in the face of danger and appears dead. This may last from 40 minutes to 4 hours. During this time, the opossum lies on its side, becomes stiff, the eyes glaze over, the opossum drools, the tongue lolls out the side of the mouth, and green anal fluid may be seen. This fascinating defense mechanism helps the opossum survive an attack from a predator because many predators give up the attack if they believe the opossum is already dead. Leave the area and give the opossum a chance to recover and move on. The opossum will not respond to prodding or poking. When the opossum is about to recover, the ears move very slightly.
I know that this may not be the answer you were looking for, but it's the only way to be absolutely sure, without touching the animal. Interacting with wildlife (poking with a stick, touching it with the bare hand etc.), is no way to go.
Are there any tell-tale signs indicating an opossum is really dead?
As mentioned above, the only real sign is that it hasn't made a single movement (the ears ;)) within at least four hours. So, there aren't any real tell-tale signs.
Of course, if the head is apart ... Well, I think you got the concept.
Would the flies be buzzing around it if it was actually alive?
The opossum releases a stinking fluid when in fear. So, yes, laying there releasing stinky fluid without any movement will result into buzzing.
Fear can cause release of a greenish-colored anal fluid. Opossums cannot “spray”, and the only way this unpleasant-smelling body fluid can come in contact with you is if your clothes brush the anal area. It washes off easily.