Exclusionary tactics

Where was I?
You had bats in your belfry.
Hey, no comments from the cheap seats!

  Ok. So, I have bats. You can't kill them; for two reasons.
  One, bats are good for the environment. They eat insects; and not just any insects: insects that are commonly referred to as pests. There are two common species of bat in my area: the large brown bat, and the small brown bat. The small brown bat likes to eat mosquitos. Really likes to eat mosquitos. Individuals can catch up to 1,200 insects in just one hour during peak feeding activity. You can imagine the effect of a colony on the local mosquito population.
  The large brown bats prefer beetles. Not just any beetles. Not Beauregard the Christmas Beetle. What large brown bats consider to be a particular delicacy are potato beetles and cucumber beetles. In fact, a colony of 150 big brown bats can consume enough adult cucumber beetles in one summer to prevent egg-laying that would produce 33 million of their root-worm larvae, a major pest of corn. Big brown bats clearly rank among America’s most beneficial animals.
  The second reason you can't kill them has to do with the fact that it's really hard to do. Bats are quite resistant to the types of poisons one might use to kill other similarly sized animals, like mice. So you have to use lots of it, or stronger poisons; both things one doesn't want to do in one's own home. It's also against the law. You know, to protect the stupid from themselves.
  So they are good for the environment. You want them around. Why even bother trying to get rid of them? That is a very good question. You don't want them in your home for a couple of reasons, as well. First, they are common carriers of rabies. Outside, in their natural environment, bat bites are virtually unheard of. Inside, if they manage to get into the living areas of your home, they are frightened and confused, and bites can occur. Second, there is an undesirable property to their feces. Yes, their crap. If it builds up enough, it starts to ferment, and a toxic gas is created. Definitely a good reason to get them the heck out of there.
  So, it's the old conundrum: can't live with 'em, can't kill 'em. What to do? Well, you have to perform a bat exclusion. Don't worry, it doesn't involve sitting in a circle, holding hands and chanting. What it does involve is finding a way of letting them get out of the attic without letting them get back in.
  Enter Charles Robertson, bat exclusionist extraordinaire. An exclusionary procedure involves four steps. Step one: locate all points of bat egress. There are always two, and sometimes three or more. Step two: Using high quality caulking, combined with physical barriers if the openings exceed one half inch in width, seal all possible openings into the structure, with the exception of the two primary points of egress. Step three: place exclusion shields over the two remaining openings. wait for all bats to exit premises. Step four: seal remaining openings.
  I know, I was going too fast. I'll go back to step three. An exclusion shield is a device that allows the bats to exit, but not to re-enter. The most common exclusion shields are simply plastic or nylon netting hung down over the holes they use to enter and exit the building. Bats have a somewhat unique way of taking flight. When they take off, they drop for about a foot until they get their wings open. An exclusion shield like the one shown here allows them to "fall" out of their doorway, but when they try to fly back in, following a more direct flight path, they encounter the net and are unable to get to the opening. This wasn't good enough for Mr. Robertson, though. He likes bats. He didn't want any of them getting caught up in the netting and hurting themselves.
  He wanted to determine the exact species of bat living in my attic. If he could identify them, he would know what frequency their sonar-like sounding system worked on. Then, he could pick a netting with holes of a very specific size, that would present itself as solid to the bat's sonar. As the bats approached where they thought their door was, they would not be able to "see" it, and would veer off. Very humane.
  To that end, he clambered up into my attic and started his scouting around. He had a tiny microphone contraption he pointed around and listened for the amplified sound of leathery little wings rustling. Once that pointed him in the right direction, he used a low intensity light to suss out where the creatures were roosting. After several minutes, he climbed back out and announced that we had a small colony of "Big Brown Bats" in our attic; only about 100-150 bats. Yeah. Small. He told us he had worked on some colonies of up to 1500 bats.
  The netting had to stay in place for three days, to be sure that all the bats inside the building had left. Apparently, a bat can go without feeding for as much as 48 hours, but on the third day, they absolutely have to come out and eat. After 72 hours he sealed up the two "bat doors" and presented me with a bill for $1500.00. No that is not a typo. There are the correct number of zeros in that amount. One thousand, five hundred dollars. Expensive, but we felt it was worth it. According to everyone we had talked to, he was the guy to get it right, and he gave us a two year guarantee of bat freedom. It's been ten.
  There was still the question of how the bats had been getting into the house in the first place. "Oh, that's easy," he said. "Through the basement." Our blank stares and drool must have clued him to the fact we didn't understand, so he filled us in.
  Your basement is unfinished, right? Right. They only got into the house in late July, right? Right. And they were only two to three inches long, right? Right. They were babies, he tells us. Here's the deal. The mama bat is taking her youngster out for his early flying lessons outdoors. This usually happens about the third or fourth week of July. She leads him to the edge of the attic, and hops over the space between the inner wall and the brick. The young bat misses the hop, and falls down into the stud bay. Well, bats almost never climb up. To a bat, down is out, so the baby bat climbs down, and down, and down. He can worm his way through openings only 1/4 inch wide. Eventually, he finds his way all the way down to the basement, where the walls are open and he can escape into the house. At some point, in his search for a further escape, he finds his way under the basement door and into the main floor of the house.
  In my expert opinion, I'd say our incredulity showed on our faces, because he led us down into our own basement, where he scouted around for a few seconds and picked up something from the floor.A really small, black something. He held it out on the palm of his hand for us to see. "What's that," I asked. He smiled. Bat dropping.