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Volume 38 Issue 17 • August 21-27, 2008
now in our 37th season

Creepy Crawlers

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

Editors Note: Be warned, this article is not for the faint of heart!

One of the most visceral fears many people harbor is the fear of spiders. In fact, some of you may not even want to read this column and instead should take a calming walk. Although we are much bigger than spiders and are usually aware of the important role they play in our environment, we still tend to view them with dread. My mother was so afraid of spiders that she wouldn’t let us use the word “spider” in the house; we had to say “arachnid” which was probably my first scientific word. Arachnophobia, or the abnormal fear of spiders, is a very common phobia. The etymology for arachnophobia is simple and direct from the Greek words “arachne/arachnos” for spider and “phobos” for fear. Phobos was the embodiment of fear in Greek mythology, and he accompanied his father Ares into battle. According to Greek mythology, Arachne was a conceited weaver from the town of Lydia who claimed that her skills surpassed Athena's. They had a contest where Arachne was declared the victor, and in her rage, Athena turned her into a spider.

Fortunately I did not inherit this fear (although my brother did), and I am able to enjoy the spider nature walks and research being done on island by Nantucket Biodiversity Initiative (NBI) funded researchers Andrew Mckenna-Foster and Cheryl Comeau Beaton. Before we learn more about what types of spiders can be found on the island, it is helpful to learn a bit more about spiders in general.

Spiders are the most familiar of the arachnids, which also includes the especially lovable scorpions, harvestmen, ticks, and mites. Spiders are in the order Aranaea as distinguished from the ticks and other arachnids. Arachnids are a class (Arachnida) of joint-legged invertebrate animals in the subphylum Chelicerata and the phylum Arthropoda, which includes animals with hardened, jointed exoskeletons. A close cousin, the horseshoe crab, is in the same subphylum and phylum as spiders, but in a different class (Merostomata, i.e., “mouth surrounded by legs”). Like horseshoe crabs, spiders must molt to grow larger; many of the terrifying objects that look like dead spiders are actually old molts. Arachnids are chiefly terrestrial arthropods, but are also found in fresh water and, with the exception of the pelagic or deep zone, in all marine environments. It is commonly understood that arachnids have four pairs of legs, and that arachnids may be easily distinguished from insects by this fact (insects have six legs or three pairs).

Interestingly, arachnids generally have a total of 6 pairs of appendages - two pairs of which have become adapted for feeding, defense, and sensory perception. The first pair of appendages, the chelicerae, is used for eating and defense. The next pair of appendages, the pedipalps, has been adapted for feeding, locomotion, and/or reproductive functions. Since this is a family column, I won’t go into much detail on the pedipalps, but let’s just say, they can be a very obvious feature.

All spiders produce silk, a thin, strong protein strand extruded by the spider from spinnerets most commonly found on the end of the abdomen. Many species use silk to trap insects in webs, although there are several species that hunt freely. Silk can be used to aid in climbing, form smooth walls for burrows, build egg sacs, wrap prey, and even for flying. Spider silk cannot be dissolved in water and is the strongest natural fiber known. Spiders produce seven kinds of silk, ranging from the sticky stuff to trap and wrap their prey to super strong threads for support, but no one spider can produce all seven. The military and other federal research groups specifically focus on producing synthetic versions of silk for a variety of combat and industrial uses.

More fun spider facts: most females are larger and stronger and will eat the males; spiders have two kinds of breathing organs - tracheae and book lungs; and spiders typically have eight eyes although only a few have good eyesight. Spiders usually depend on detecting light changes or rapid movements for hunting, defense, and communication. Spiders have evolved numerous ways to catch their prey, which is mostly insects but can also be frogs, fish, lizards, snakes, and birds. Some spiders are masters of disguise, blending into their background so that they look like parts of a flower or a leaf. Others hide under "trapdoors," jumping out of their hiding places to snatch a passing meal. Still others can leap many times their body length, covering great distances to grab their prey.

Most spiders can inject venom to protect themselves or to kill and liquefy prey. Only a few species (brown recluses, banana spiders, black widows, common sac spiders) have bites that can pose health problems to humans. Many larger species' bites may be painful, but will not produce lasting health concerns. Spiders also tend to be pretty timid and non-aggressive and rarely bite unless mishandled, cornered, or injured. Spiders are found all over the world, from the tropics to the Arctic, with some extreme species even living underwater in silken domes they supply with air, and on the tops of the highest mountains. And to answer a question I had a few weeks ago, NO, we do not have brown recluse spiders on Nantucket unless they took a very long plane or car ride. Go to http://spiders.ucr.edu/images/colorloxmap.gif to see the extent of the range of brown recluse spiders. The two best known venomous spiders in the U.S., the black widow and the brown recluse, have not been proven to have caused any deaths in more than two decades due to the accessibility of antivenom.

Basically, there are two types of spiders: web spinning spiders and hunting spiders. Web spinning spiders include orb and funnel weavers. Orbweaving spiders produce the familiar flat, ornate, circular webs usually associated with spiders. Orbweavers come in many shapes and sizes, but the brightly colored garden orbweavers, Argiope, are the largest and bestknown. The yellow garden spider, Argiope aurantia, is marked with yellow, black, orange or silver. The female body is more than one inch long with much longer legs. It is also known as the black and yellow garden spider and sometimes the writing spider because of a thickened interwoven section in the web’s center that looks like a zipper. We have many garden spiders on Nantucket. Male Argiope, often less than one quarter the size of females, can sometimes be found in the same web with the female. Garden orbweavers are so named because their webs can be found in fields, on fences, around homes and in other locations. Here at the Field Station, one of my favorite spiders is a tiny, bright green spider that lives on the red cedar (Juniperus virginiana) and is a member of the Tetragnathidae family (long jawed orb weavers).

Hunting spiders include the jumping spiders and wolf spiders. Jumping spiders, all of which are in the family Salticidae, are among the most interesting spider groups to watch. Jumping spiders come in many sizes and color patterns. Active hunters during the day, they have good eyesight, relying primarily on movement to locate prey. They stalk their prey before attacking in a fast leap. Jumping spiders put out a line of webbing when they jump and can sometimes be seen dangling from this silken dragline after a leap that fails. Many jumping spiders are bold, stocky and often brightly colored. They often have conspicuous bands of black and white on their bodies or legs. Others have velvety red abdomens and some even have metallic colors on the chelicerae. Jumping spiders have eight eyes, with one large pair in the front. Like most spiders, jumping spiders are not considered hazardous to humans and are unlikely to bite unless cornered or handled.

Wolf spiders hunt at night. Usually brown and black, they may have longitudinal stripes. Wolf spiders are large and often seen under lights. They can be seen at night when their eyes reflect light from a flashlight, headlamp or car headlight. Members of the genera Rabidosa and Hogna are some of the most conspicuous wolf spiders. They form webbing only to provide daytime shelter, not to capture prey. Many wolf spider females carry their egg masses below their abdomens until after the eggs hatch. Young spiderlings cling to the mother’s abdomen for a short time after hatching. Wolf spiders frequently enter homes and backyards but pose no danger to people.

The spider that usually jumps first to mind when thinking of venomous creatures is the black widow spider, Latrodectus spp. This adult female spider is readily identifiable because of its unique coloration: a shiny black body with red hourglass on its belly (not on its back as lots of people think). However, the black widow looks very different as a juvenile because it starts out life bedecked in tan and white stripes. As spiderlings mature, more black pigmentation is deposited in the integument with each molt until they turn completely black. Males retain the coloration of the juvenile striped pattern

This leads us back to our intrepid spider scientists working with the assistance of the Maria Mitchell Association (MMA) and with funding and support from the NBI. So far, Andrew Mckenna-Foster (University of Wisconsin-Green Bay) and Cheryl Comeau Beaton (MMA) have found 301 species and have collected 3,762 spiders from all three islands in the past two years with ongoing work this summer. They are attempting to find out how many species are still found on Nantucket as identified by eminent arachnologist James Emerton during his island research in 1928 and 1929. In addition to their research, they conduct public walks and collection trips and enlist volunteers to help them collect spiders and become more familiar with them while also easing the distress that most people may have when they first realize they will go looking for spiders. Collection methods include using sweep nets, limb beating (trees and shrubs, not humans), pitfall traps, and the very popular spider siphon device which consists of flexible tubing, a mesh screen, metal tubes, and a small vial. You place the metal
tube around the spider you want, then suck on the other end (hopefully with the mesh in place!), and your spider ends up trapped in the vial if all goes well. Seriously, kids love it.

One of their most interesting discoveries involves a possible variant of the Northern Black Widow, Latrodectus various. They have found a color variant that features two red bars on the belly instead of the typical triangular marks. In addition, the female black widow spiders they have observed (now set up in a tank at MMA natural history museum) are much more tolerant of other black widows in the vicinity and appear to be less aggressive than normal. The captive female black widows have recently had babies and Cheryl is the proud overseer of a large brood of spiderlings. Currently, they are calling the Tuckernuck northern black widow a latrodectus sp. while they do genetic testing and additional behavioral tests to see if this is truly a new species. They are also investigating a purseweb spider species called Sphodro rufipes that they found in relatively high densities on Tuckernuck that builds its web in grass and dead sticks instead of on trees or rocks.

Spiders are terribly misunderstood; once someone has heard of a relatively rare venomous attack, almost all spiders are lumped into the category of "squish first and ask questions later." Overall, spiders are beneficial to humans because they eat many insect pests that infest our food, are vectors of disease (flies, mosquitoes), or are aesthetically-challenged (cockroaches, earwigs). And spiders are not very susceptible to pesticides. The highly mobile eight-legged animals will come back to an area that's been sprayed because, unlike insects, they're not strongly affected by residual pesticides. To prevent spiders from coming inside the house, arachnologists suggest sealing off any cracks or gaps where spiders can slip in. But to control insects that can cause damage to your property - such as termites- why not let their natural predators, spiders, inside to do the work? And if you get a chance, join Cheryl and Andrew on a spider collection walk to gain a new respect and admiration for our 8 legged friends.

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