Signs of Spring 12: Spiders and Stink Bugs

Photo by D. Sillman

A couple of days ago I was down in my basement washing up my beer making equipment in preparation to brew a batch of a double IPA for the coming summer. The hardest part of beer making is getting everything clean and sanitized so that there are not too many extraneous, competing microorganisms battling with the introduced yeasts to take the sugars of the brewing wort into odd, biochemical directions. You want as simple of a microbial community as possible in your fermenting system in order to guarantee a predictable (and delicious!) outcome. Brewing, then, is just another branch of applied ecology!

Anyway, making beer mostly involves washing and cleaning equipment, and I was leaning over the big laundry tub sink in the basement, scrubbing my ale pail with hot, soapy water when a delicate cellar spider (Pholcus phalangiodes) (photo above) drifted down on a silk strand from the ceiling over the sink. I did not want the spider to fall into the hot water so I pinched my thumb and pointer finger on the silk line and tried to gently move it over to the safety of the wall shelf. The spider, though, reacted violently to my touching its drop line and immediately released its thread and pitched itself into the hot water below.

I have a long, mutualistic relationship with our basement spiders, and this sudden death (almost an arachno-suicide) upset me. These spiders are active and abundant all year round in our basement and besides eating each other also, I am sure, consume a wide variety of insects that might otherwise thrive in the cool dampness of the basement. I have even seen brown, marmorated stink bugs caught up in the webs of these small spiders (although I have only seen larger, more robust spiders actually feeding on the stink bugs (see discussion and pictures below!)).

So I looked up at the ceiling from which the pholcid spider had come and saw the reason why it was so eager to get away. Wedged next to the floor joist was a large, fishing spider (Dolomedes tenebrosus.) who had been undoubtedly hunting the frail little pholcid.

Photo by D. Sillman

Fishing spiders are impressive! Females have a body that can be slightly more than one inch long (about the length of a chap-stick tube!) and legs that can be 2 to 3 inches long! Holding one of these spiders in my hand (which is hard to do because they are very shy and hard to catch!) their legs easily span the width of my palm. We have had fishing spiders in our basement and garage for many years, but I hadn’t thought of their “super-predator” role in our basement ecosystem before. The pholcid spiders, who are active predators themselves, may be the primary prey of these larger arachnids.

The fishing spider stayed in its spot up on the ceiling until I finished scrubbing the ale pale. It was waiting for another snack to wander by and showed amazing patience and focus.

I have written about brown marmorated stink bugs four or five times over the past five years. Their sudden appearance in Western Pennsylvania in the fall of 2010 and their explosive numbers in the springs and falls ever since have made them a very unwelcome sign of both spring and fall.

The brown, marmorated stink bug (scientific name: Halyomorpha halys) is a native of northeast Asia (Japan, Korea, and China) and, apparently, is just as annoying there as it is here! Its use of human habitations as hibernation refuges, and its ability to communicate via pheromones and then aggregate in great numbers in some selected house, barn, porch, garage, or any other stink-bug-determined-suitable building makes their presence both in their native and also in their invasive regions impossible to ignore.

It is thought that this insect was first released into the United States in Allentown, PA in 1996. It apparently traveled from northeast Asia in a shipping container that was delivered either to the port of Philadelphia or Elizabeth, New Jersey and then trucked to Allentown. Five years later this new, alien, invasive species was recognized and identified by entomologists at Cornell University, but by then significant populations were being observed throughout eastern Pennsylvania, New Jersey and New York. This insect has spread to thirty-five states primarily in the eastern United States. It has very large populations in Pennsylvania, Maryland, Virginia, New York, New Jersey, Massachusetts, Delaware, Ohio, and North and South Carolina. It has also spread to California and Oregon allegedly via a car driven by a person traveling from Pennsylvania to California in 2005.

There is a consortium of university and government researchers who are looking into the basic ecology and biology of the brown marmorated stink bug. Their goal is to come up with effective control measures to stem this growing biological invasion. The group (called “Stop BMSB”) is funded by the US Dept. of Agriculture and includes fifty researchers from tem universities (including Penn State!). They even conducted a “citizen’s science” survey last fall to try to determine some of the ecological and behavioral features of this bug. Their “2014 Great Stink Bug Count” asked homeowners to go out around their houses every day to determine the numbers and locations of any stink bugs that are present. Every little bit of data might help!

But here is the interesting thing: when the stink bugs first made their appearance here in Western Pennsylvania almost every potential predator was actively repelled by their pungent scent. Spiders, birds and almost every other type of possible insect eating invertebrate and vertebrate species actively avoided contact with the stink bugs, and, subsequently, their populations grew out of control. In the fall of 2013 and in the spring of 2014 we caught thousands of stink bugs in and around our house. We filled up cases of one liter, plastic bottles with their carcasses! Last fall, though, the huge numbers did not come, and this spring I have caught maybe a dozen total stink bugs over the past month. A far cry from the thousands of just twelve months ago!

Photo by D. Sillman

What has happened? Spiders are now actively eating stink bugs. The picture Deborah took of this jumping spider (Phidippus spp.) chewing its way into the captured sink bug is a great example! Birds (especially titmice and chickadees) flare up to the window screens of the house and snag unwary stink bugs. They fly them over to nearby branches and gobble them down! The predator guild of our surrounding vertebrate and invertebrate community has adapted itself to this new (and formerly incredibly abundant) food source! Control has been achieved, at least in the area immediately around my house!

Anyway, my basement spiders are trapping stink bugs even while they are being hunted by the larger, fishing spiders. The birds and outdoor spiders are also establishing a new equilibrium with, apparently, controlled stink bug menace. Invasive species are not always this quickly contained. If anyone is having any stink bug experiences this spring, please let me know!

Next week, another great topic! Gypsy moths! The fun keeps rolling along!