Friday, August 12, 2011

In the time without bats

Bats are virtually extinct in Nanticoke, and possibly throughout Northeastern Pennsylvania. While some people who live in the country have reported seeing some bats, they have been completely absent from the low skies of Nanticoke as twilight darkens into night. Up until now they have been a part of the ecosystem here, flapping in seemingly erratic paths across the not-quite-dark sky in search of insects. But now they are gone, apparently all of them.

The culprit is a fungus that produces a condition known as White Nose Syndrome, which disrupts the life cycles of bats in a way that may prove lethal. It has been reported for years throughout Northeastern Pennsylvania, primarily as a disease of cave-dwelling bats, but apparently now it has moved on to the more suburban bat populations in places like Nanticoke.

Are the bats gone for good? Maybe. Maybe a resistant population will emerge. Or maybe the disease will vanish as its host population crashes. But for now, like honeybees just a few years ago, the bats appear to have been removed from the ecosystem.

Ecosystems are funny things. They tend to be robust. Hit them in the wrong way - say, introduce predatory cats and Dutchmen and egg-eating rats to the Dodo population of Mauritius - and you will do permanent damage, eliminating a part of the system that can't easily be replaced by native or imported species. But other perturbations to an ecosystem may produce less dramatic adjustments as other species move in to fill available niches. The collapse of the honeybee populations is an ongoing tragedy and crisis, but it did not result in the pollination disaster that was feared; other species flew in to pick up the slack, feast on the pollen, and incidentally do the job of pollination that had previously been done by honeybees.

With bats gone, I got to wondering what would happen. I didn't have to wonder for long. A flying insect infestation on our back porch forced me to resort to using old-fashioned ribbon fly paper, which serves as a grim sampling system for insect populations. The physical evidence revealed an assortment of insects I had never seen before, in very large numbers. Most likely a consequence of the disappearance of insectivorous bats.

OK, fine. No bats, more insects, because there are no bats keeping their populations in check. But bats aren't the only things that eat insects. What about...spiders?

I had visions of an explosion in the spider population. Spiders living in communities of hundreds, all weaving their webs together in a sort of spider village. (I actually saw this happen once, years ago, under the lights of a local gas station.) Or maybe spider webs five, ten feet across, loaded with trapped prey? Or just spider webs everywhere, a nighttime landscape thick with sticky webs and their perturbed proprietors?

On the spider front I have noticed an increase in the number of highly ambitious spider webs, ones with horizontal guy lines of five or ten feet. And these lines tend to be thick and obvious, at least in the right light - more than once I have ducked under a line in my travels through our yard, careful not to destroy the web it was supporting, only to walk straight through it on my return trip, sometimes catching it across my forehead but occasionally right across the eyes. And these webs have seemed strong, less like walking through a gossamer strand and more like plowing through a bit of sticky dental floss strung across your path.

Last week I was nearly done mowing the lawn and I took a break in an Adirondack chair. It was getting close to sundown, and I spied a few birds careening through the sky above me, maybe twenty or thirty feet overhead. Then I noticed there were a dozen or more birds1, all swooping and diving through the air. Feeding. There must have been a swarm of insects up there, and they were eating through it like sharks through a school of sardines.

Today I had just wrapped up mowing the lawn again, and I was making my way through the backyard, and was surprised by the sight of another group of flying, insect-eating predators. Not birds this time.

Dragonflies. Over a dozen of them, all swooping and diving just six feet or so off the ground.

A few weeks ago a friend and I were traveling south on interstate 81 near Hershey, Pennsylvania when we came upon a traffic jam. We were stuck; the nearest exit was 3.9 miles away, according to my friend's GPS. All we could do is sit there and endure.

After a few minutes, a red dragonflyish thing landed on the antenna of the car in front of us and just sat there. I had my camera with me, so I pulled it out and started taking pictures.

I would later tentatively identify the insect as a red Banded Pennant, a dragonfly relative. (It may have been a Halloween Pennant, though I would swear that the body of this insect was candy apple red.) I had never seen one before, but I realized I had been seeing a lot more dragonflies than usual this year. Several other friends confirmed that they had noticed this, too. But what could be the cause? At first I speculated that it might be related to the collapse of the bat population - assuming that bats were dragonfly predators. But perhaps the truth is that bats were actually dragonfly competitors, feeding on the same insect populations as the dragonflies, and in the absence of their bat competitors, the dragonfly population exploded.

So is this a "new normal?" Are bats gone from these parts for good? I have no idea. I hope not. I always enjoyed seeing them flapping erratically across the darkening sky, and they played an important role in managing insect populations. Without them, there will be consequences. Maybe for the spiders and birds and dragonflies, these consequences will not be entirely bad. But the loss of any species is a tragedy for its ecosystem.

1. Birds, not "bats" as I originally typed. That error pretty much negated the point of this post.

No comments: