Group Transport by Ants

A group of 100 ants Pheidologeton diversus was able to transport a 10cm earthworm weighing 1.92.g (5000 times the weight of a single ant) at .41 cm/s.
Ants in solitary transport can only carry 5 times their wight at 1cm/s.

Is there an advantage to group transport?
When and how does an ant know that it cannot carry an item alone?
How are nestmates recruited when help is needed?
How do several ants cooperate and coordinate their action to actually transport the item?
How do ants ensure that there is the right number of individuals involved in carrying the item?
How does a group of transporting ants handle deadlock (when something is stuck)?