Bats are generally wonderful creatures and helpful to us. For example, they eat lots of insects that are annoying (like mosquitoes) and pollinate lots of plants. Of course, they also eat lots of good (for us humans) insects but the insects still seem to be able to fulfill their environmental niches so all is good.
And they are flying mammals which is, of course, cool.
But bats also transmit virus to us, which do us lots of damage. As the video explains as we have intruded into bat territory and chopped down their natural feeding spots we have come into contact with them more. And because bats evolved to be very resilient to virus and they live in large colonies (for easy transmission of the viruses to lots of bats) they can host viruses and survive long enough to infect lots of other bats, and to infect us if we meet them.
I actually didn’t know this (mentioned in the video): most viruses have a very difficult time surviving even with temperatures a bit above the normal human temperature (98 degrees Fahrenheit). Bats, while they fly, have internal temperatures that soar to 104 degrees (40 degrees centigrade) which kills off most viruses, but certain hardy viruses survive. This also explains why we run fevers when we are sick (which then can kill off viruses) – which I am sure I learned at some point but I forgot. But for the bat viruses that strategy doesn’t work.
Bats, of course, are not impervious to disease. In the USA a disease has killed more than 90 percent of the cave bats in Eastern states.
One of the causes of the current ebola outbreak is believed to be people eating bats in West Africa.