Friday, October 30, 2009

Halloween Special: Ghosts and Pirates

What is more appropriate for Halloween than ghosts and pirates? We are not talking about trick-or-treat costumes, though, but spiders. Come to think of it, what is more appropriate for Halloween than spiders?! Just last week I found both kinds on an unseasonably warm night (October 21) here in South Deerfield, Massachusetts.

Both ghost spiders (family Anyphaenidae) and pirate spiders (family Mimetidae) prowl in search of prey. The similarity ends there, though, as they don’t resemble each other in the least, and their lifestyles are very different.

Ghost spiders are, not surprisingly, pale in color for the most part, and generally nocturnal in their habits, haunting foliage in pursuit of insects to eat. By day they hide in curled leaves that they tie together with silk.

Despite their name, ghost spiders are not very intimidating to humans. Adults reach a maximum of only a bit more than 8 millimeters. This one, a specimen of Hibana gracilis, was probably about six millimeters in body length. Big enough to take down the midge it is munching on, though. I think spiders recognize on some level the attractiveness of outdoor lighting to insects, as that is the situation I found this one in, and the pirate spider as well.

Pirate spiders are easily identified by their four eye patches and two wooden legs. But seriously, folks, the long spines on their legs help differentiate them from the cobweb spiders and sheet-web weavers that they otherwise might be mistaken for. The resemblance to other spiders is further complicated by the fact that you sometimes find pirate spiders in the snares of cobweb weavers. Their appearance there is as sinister as their name suggests.

Pirate spiders eat cobweb spiders, as well as orb weavers and other spiders. They dispatch the rightful owner of the web by biting the other spider on its legs, feeding from one after the other until the victim is totally drained. One reason for attacking the legs of its prey might be that the jaws of pirate spiders are fused at their base, not permitting the spider to open its mouthparts wide enough to bite other parts of its victims.

The specimen I found last week was Mimetus puritanus, the most common species in the eastern United States. There is a total of fourteen species in the genus in North America, however, and another ten that remain undescribed (awaiting the assignment of names by arachnologists).

BOO! Just making sure you are still paying attention. Ar-r-r-r-g, matey! Be on the lookout for ghosts and pirates in your own neighborhood.

Tuesday, October 27, 2009

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.

Sunday, October 25, 2009

The End of Extension in Michigan?

My good friend Bug Girl just posted a very disturbing entry to her own blog. Apparently the Michigan legislature intends to abandon the state’s Cooperative Extension Service.

This is just simply embarrassing, akin to the legislation in Kansas concerning evolution and creationism. Is that the kind of reputation that Michigan wants? Of course not. Extension agents help people across the entire globe because they are literally and figuratively plugged into networks of other professionals, trading ideas and helping each other in myriad ways. No state can afford to essentially operate in a social, economic, or scientific vacuum, but that is what is going to happen if the legislators don't see the error of their ways.

It is my humble opinion that there are no more important people than extension service personnel because they serve as the public face of science, educating the masses in a variety of formal and informal ways. They also serve as mentors to young students of science and agriculture via 4-H and other programs.

I urge you to lend your voice of support to the comments calling for an end to this budget-cutting nonsense over at Bug Girl’s Blog. Together, we can stop this and help ourselves as well as Michigan residents who would be so terribly hurt by an end to the Cooperative Extension Service. Thank you.

Tuesday, October 20, 2009

Spider Season


Fall is also spider season, at least in temperate climates. I am asked about spiders much more often in autumn than at any other time of the year. Why is this so? What does it mean?

Orb-weaving spiders in particular are much more conspicuous later in the year than in the spring and summer. This is true for several reasons. The spiders are mature, and therefore larger, for one thing. Females are also competing for the best “web sites” to optimize their prey-catching opportunities. This means that some end up spinning in less-than-ideal spots, like across your door. They could conceivably be there by choice, though. Spiders are quick to learn that outdoor lighting attracts lots of insects, so your front porch might be great real estate for the arachnids.

Indeed, a few species seem to actually prefer human constructions. The “barn spider,” Araneus cavaticus, is seldom found anywhere else. The females are quite large by North American spider standards, and can be rather intimidating when they stretch their snares across the rafters and under the eaves. Ironically, the webs are rather small compared to the spiders themselves.

Females of many orb weavers spin their webs at night, remaining concealed in “retreats” in curled leaves and other shelters by day. They connect a “signal thread” to the hub of their circular snare to literally keep them in touch with the web, alerting them to the impacts of any insect victims that might become entangled during the day.

Other orb weavers sit in the hub (center) of their webs at all times, like the “cross spider,” Araneus diadematus, pictured at the top of this entry. When disturbed, the spider may shake violently in its web, perhaps startling the potential predator into abandoning its intended attack.

While female spiders are stay-at-homes, male spiders wander in search of mates, even those species normally confined to webs. Autumn is the season in which many of these nomadic suitors find there way indoors by mistake, freaking out female humans in the process. The male spouse is then recruited to dispatch the male spider. I encourage folks to consider simply ushering the spider into a container and taking it back outdoors where it can resume its romantic pursuits in a more appropriate habitat.

Mature male spiders can often be identified by their more slender bodies, longer legs, and modified “palps” or “pedipalps,” leg-like mouthparts that often resemble miniature boxing gloves.

Some spiders simply hunt on foot and don’t bother with a web. One of the more common examples of this kind of hunting spider are members of the genus Trachelas in the family Corinnidae. They are often encountered indoors at this time of year. Once considered mildly venomous to humans, they are now classified as harmless.

Wherever you find spiders, enjoy them in their roles as master weavers and pest control patrol. You can safely relocate indoor spiders with the “cup and card” trick. Simply place a cup, glass, or other container over the spider, slip an index card under both the spider and the mouth of the container, turn them over, and take them outside. The spider and your spouse will thank you for it.