Ants
more than one lynx is call lynxes
you call them possums if your talking about more than 1
It is more efficient to have only one unit slowed by pregnancy than thousands.
More than one fisherman is fishermen
More than one platypus is two or more platypuses. The plural is not 'platypi'.
They don't have a tail. The fire ant as one but... its more of a stinger
There's a thing some people call ant traps. One places bait inside the ant trap, so when the ants wander into it looking for food, one can dispose of them easily.
Fish
swans
Pegasi I think.
Vampiresses.
Polygamy.