I See Dead Spiders

I have been almost literally wading through vials of dead spiders in my lab at the University of Massachusetts (Amherst) the last few weeks. My supervisors had tried to come to terms with a real arachnologist in Canada to identify the pitfall trap specimens from last year’s samples, but apparently international relations were too complicated and it fell to me to try and make heads and tails (cephalothoraxes and spinnerets?) of the many members of the order Araneae that were trapped last summer.

The chemicals and processes used in collecting, cleaning, and preserving the specimens often leaves them in less than optimal condition for identifying them later on, and the biggest challenge I’ve had has been finding intact specimens, or at least assembling all the parts scattered throughout a given vial. Legless specimens abound, as do those without abdomens.

Another problem one encounters is finding mature adult specimens. Many specimens can be determined to the family level of classification as immatures, or even spiderlings, but genera and species can be impossible to conclude without having the external genitalia to examine. The majority of specimens I find to be juveniles or “penultimate adults,” the term for spiders one molt removed from adulthood. Arg!

Still, I am learning a great deal about spider anatomy and am able to execute identifications to a respectable degree despite the obstacles. I have at my disposal several fine literature references as well as excellent online resources. Ultimately, I must rely on patiently putting the specimens through “keys,” documents in the form of couplets that direct you to other couplets and eventually take you to the name of a genus or species. When it works, it is a joyous occasion. More often than I’d like, though, the result is one of sheer frustration.

The diversity of the spider fauna that I’m finding is truly amazing. Among the more dominant families are the Linyphiidae, which includes the tiny “dwarf spiders,” subfamily Erigoninae. There seems to be no end to the number of different species, and some of them sport bizarre formations on the cephalothorax . Males of Oedothorax trilobatus sport tumor-like swellings that give the species its name. Meanwhile, some males of Walckenaeria communis can have a horn-like extension of the cephalothorax. The spiders themselves measure only about two millimeters in total body length.

At the other end of the spectrum are relative monsters like Wadotes hybridus, a member of the hacklemesh weaver family Amaurobiidae that can reach 14 millimeters at maturity. These are powerful, brutish arachnids with heavy legs and enormous chelicerae (jaws).

You can see some of the other strange and wonderful species I’m identifying and imaging by following my string of images at Bugguide.net, which start with the most recent uploads. Live vicariously in arachnid land.

A Day in the life of an Entomologist

I thought I would share just how exciting it is to be in a laboratory doing critically important work as an entomologist, processing pitfall trap samples. I’m kidding, of course, when it comes to the “exciting” part, but it truly is important.

The project I am involved with is striving to develop a protocol for assessing the ecosystem health of forested watersheds, a common yet complex habitat in the northeast U.S. The University of Massachusetts has partnered with the Massachusetts State Department of Environmental Protection and the United States Environmental Protection Agency to carry out this research. Dozens of people have been working in the field and in the lab for nearly ten years already. What started as one person’s project has mushroomed into something much greater. Ok, I know what you’re thinking: How does this affect me, Al Franken?

The habitat under scrutiny here includes many streams that run for most of the year, but run dry in the heat of the short summer. Hence, pitfall traps can be set in mid- to late July in places that are under water the rest of the year. Even then, a freak storm can set the watershed running again and flood the traps, or a beaver can dam the place and do the same thing. The former event happened last year, so I am able to process only a portion of the total pitfall trap samples collected in 2008.

A pitfall trap is a container sunk into the soil (or sand, or other such substrate) such that the lip of the container is flush with the surface of the substrate. Any insects, spiders, mites, and other creatures that come strolling by then fall into the trap. A trap is typically set for a week before being collected and the contents preserved in ethyl alcohol.

The resulting sample I see is in a plastic container with a label detailing the site identification and plot number, and date the trap was set and the date it was collected. Comments indicate the type of location (such as a sphagnum moss mound) and the condition the trap was found in when it was retrieved. I pick out the insects, arachnids, and other invertebrates that I can see with my naked eye, placing each taxon into its own glass shell vial. The vial is labeled both inside and out with the plot number, site ID, and taxon name (Coleoptera – beetles in this photo). The inside label also includes the number of specimens.

I also record the same data on a sheet, counting the number of specimens as I go. Once I’m done with the “big” specimens, I then put the container under the microscope and sort out the smaller things. The effect the alcohol preservative has on the specimens can be dramatic. Spiders fall apart. Even beetles start losing legs and abdominal segments. Springtails, normally pigmented, become literal shadows of their former selves, the alcohol having “cleared” them. It is a strange sight to see a ghostly springtail float across your field of view (cue the spooky music).

The amount of debris in a given sample, and/or the number of invertebrates, can greatly extend the time it takes to process a sample. It can also be very confusing at high magnification to tell a segmented plant part from an insect larva!

Stay tuned for further episodes in the life of an entomologist. Next week, Eric goes insane while trying to identify micro-Hymenoptera to family level….