||Susan Riechert as seen on Going to Extremes and Spiders!: Spider Canyon
Click on Susan's photo to read a brief bio.
I saw your show in my science class and what I want to know if have you ever been afraid of spiders or have you always had a fascination with our 8-legged friends. J.W.
Have I ever been afraid of spiders? No. I grew up in a semi-rural area and a group of friends and I spent our summer vacations collecting butterflies, raising frog eggs through the tadpole stage to adults, and making forts out of natural materials. No one ever told me to be afraid of spiders and so I wasn't. I have to admit that I am not real fond of snakes. That is just because I have been bitten by many over the years and they are a bit hard to hold on to when they start squirming, I have only been bitten by spiders a couple of times when I have accidentally squooshed them. No worse than a mosquito bite and when they get loose, they just think I am a tree to walk on. I frequently ask my colleagues to locate a spider that has gotten loose on my clothes somewhere!
If a live fire ant could kill a spider, why doesn't the poison in the ant kill the spider when it eats the ant? (asked by several viewers)
The ants I use in my studies are harvest ants not fire ants, but the question remains the same. Harvest ants have one of the most potent venoms of all hymenopterans (bees, ants and wasps). This is the difference between something that is poisonous and something that is venemous. Many mushrooms are poisonous. They are dangerous to eat. When absorbed by the digestive tract they cause damage to the liver or some other organ. Black widow spiderlings, like mushrooms are poisonous, but ants and adult female black widow spiders are venemous, but not poisonous. They inject a venom that causes your tissue to react. Ants are not poisonous to spiders who eat them, but the formic acid they produce may make them a bit bitter (to my taste anyway).
How long is the process of making a spider web? Is it similar for all spider species? Amanda
It make take as little as 30 minutes to several hours to produce a web, depending on the spider species and the amount of silk that goes into the web. Sheet-line weavers, like Agelenopsis aperta, produce permanent webs that have a lot of silk. The energy spiders take in from about two days of feeding is invested in the initial construction of these webs. Silk is added daily to make them larger and stronger and also to repair damage done by wind and insects caught in them.
How do spiders know where to build their webs so they will safe and catch prey? Erin
Spiders respond to cues that permit them to build their webs in places where insects are abundant. Agelenopsis aperta, for instance, can detect insect odors and vibrations and will build its webs where these cues are strongest. They also look for shade and favorable temperatures when selecting a web-site. Some spider species (e.g., orbweavers) set out a few test lines of silk for a day or two at a site before building a full web. These test lines can provide an indication of the prey levels that are available at the site.
Why do different types of spiders weave different webs (e.g. funnel or orb)? Peter
Web designs have evolved over millions of years from just a few silk threads that allowed spiders to sit in a protected environment while monitoring the world outside for both prey and predators to efficient traps. Different web designs, then, in part reflect advances in trap efficiency but also where these traps are placed and what types of insects a kind of spider might expect to capture. The orb web is the most advanced of the spider webs and its open design permits spiders to place the webs up in the air currents in the flight paths of moths and butterflies. Orb webs have evolved in two major lines of spiders, in the hackled-band weavers that have a mechanically sticky web (many fine threads) and in the araneids that produce a chemically sticky spiral trap. The open space between capture lines is needed to let air pass through. Otherwise the web would be destroyed by the winds. Because of the small amount of silk used in these webs and all of the open space, the sticky silk is needed to deter the escape of the prey while the spider is reaching it.
The comb footed spiders (the black widow is the most famous example) and cellar spiders use a vertical scaffolding to knock down prey which the spider must run out and capture before it escapes. These webs also have a fair amount of structure but do not achieve the size of the orb webs. They are located in bushes, at the base of plants and on rock faces.
The sheet-line weaver webs are very sensitive to wind damage. They are generally built low to the ground or in wooded areas. Only small prey are captured on these webs. The spiders must attack larger prey items immediately. In the case of the funnel web spiders, like Agelenopsis aperta, the web serves merely as an extension of the spider's sensory system (for the detection of prey).
How do you measure aggression? What is the unit called and what tools do you use? Or do you just rate them yourself from, say, 1 to 10 or something?
Aggression in Agelenopsis aperta involves the combined interaction of two conflicting tendencies: the tendency to flee or run away (for simplicity I call this fear) and the tendency to attack (or aggression). As I have mentioned in answer to another question, each of these traits has a different mode of inheritance. We use a whole series of behavioral tests to determine where a spider fits on a range of scores from being very fearful to very aggressive. These include a spider's tendency to escalate to fighting or to retreat and withdraw in contests over web-sites, the distance at which a spider tolerates a neighboring spider, how quickly it responds to an insect encountering its web, how quickly it comes back to a foraging position after encountering a predator or predatory cue, and what prey types it includes in its diet.
Our scale is actually a relative one in most of our work. It merely predicts the position of different genetic classes of individuals relative to each other. Thus the dry woodland spiders will win contests (be more aggressive) than the riparian spiders, the cactus scrub spiders will be more aggressive than the dry woodland spiders, and the hybrids between dry woodland and riparian spiders would be more aggressive than any of the other classes as in: < hybrid dry woodland X riparian. In simulations of spider behavior, we actually assign numbers to aggression and fear components of behavior as well.
Have the hybrid offspring of the desert spider and the river spider formed a new design of webs that show qualities from both breeds' original design of their webs? Students at WAS
No, the only difference we can detect without completing genetic structure studies in the laboratory is a difference in their fitness-linked behaviors: contest behavior, territory size demanded, aggressiveness towards prey and the types of prey they will include in their diet, and boldness towards predators.
Do all spiders have 300 babies? Chris
No, not all spiders have 300 babies. The more social spiders that live in huge colonies in the tropics might have as few as 10-15 spiderlings. These colonies are family groups and there is a lot of care taken by older spiders of the babies. On the other hand, spiders that live in temporary habitats like orb weavers in old fields or along roadcuts, may produce over a 1000 babies in an egg case. These babies disperse on air currents through a behavior called ballooning. Most of the offspring are lost as they may land in parking lots, lakes, and other inhospitable environments.
You have studied some 1500 spiders in the Arizona area. Is it common to have a population of spiders that size in many similar areas throughout the country? David
Local spider populations can often be very large and in natural areas, spiders may achieve densities of 120 individuals/m2 with 100 species represented
In the story "Spider Canyon," you said you might be watching a species split into two. How do you know when you have two different species, because some species can cross breed and still have fertile hybrids. Do you do genetic test to figure this out? Mark
While two species may indeed produce fertile hybrids, this rarely happens in animals in which speciation occurs in sympatry. That is where a species splits into two entities at the same locality. What we currently have with the spider canyon problem is hybrid breakdown. The hybrids are indeed fertile, but there is a behavioral problem that limits their survival and reproduction. This problem becomes even more pronounced in subsequent generations involving hybrid individuals in the riparian habitat: individuals that either attack all potential mates or run from all potential matings never produce offspring. This represents a postzygotic (after offspring production) barrier to population mixing and is a waste of gametes to the individuals that breed with unlike types. It is the first stage in the splitting of one species into two. To prevent wasted gamete production, some kind of prezygotic (before offspring production) deterrent to mating with unlike types should evolve. I predict that this could be in the form of female discrimination against males of unlike type. Prezygotic barriers often involve courtship problems. If this discrimination mutation were to arise, then hybrids would no longer be produced and the two populations would probably diverge over time (1000s-millions of years) as a result of genetic drift (random mutations) into distinct species that would no longer produce viable offspring.
Will spiders bite for no reason, or are they like bees and bite only if you make them mad? Kevin
I have never had an Agelenopsis aperta bite me despite the fact that I hand collect them and do all kinds of nasty things to them like heating them up to look at heat stress and placing paint marks on their abdomens. Spiders generally have very poor eyesight and view humans only as objects to walk on. Most spiders, then will bite only if they find themselves being crushed as when they are in a piece of clothing that you put on. This may also occur when you walk into a web where the spider is pinned between its web and you. (Most black widow bites occurred in outhouses by this mechanism.) I would not stick my finger between a tarantula's fangs though. The same is true for the large wolf spiders.
I saw the "Spider Canyon" story on Frontiers a couple of seasons ago. I'm curious how your project is going. Can you bring us up to date on the progress and recent findings in your research? Barry
We have made a lot of progress on the spider canyon project since the segment was produced a few years ago. We have found, for instance, that matings between the aggressive arid-land spiders and the more fearful riparian spiders account for 10% of the matings in most years (hot and dry). In unusually wet years, the between population mating is much lower (around 5%). In wet years, the arid-land spiders may obtain sufficient food at web-sites in their native habitat to prevent them from wandering in search of better habitat. We have also learned that over 20% of females in the riparian population run from all potential mates, while another 5% attack all potential mates. This is a direct consequence of the mixing of arid-land and riparian genes, and as described in the answer to the question above, represents a postzygotic barrier to gene flow between the two local populations.
Through selected breeding experiments, I am currently learning the relative contribution of the genes controlling aggression (located on the sex chromosomes) and those controlling fear (many genes on the autosomal chromosomes) to various aspects of spider behavior. For instance, spider fighting behavior in contests is largely controlled by the genes for aggression. This is also the case for what is called superfluous killing (i.e., your eyes are bigger than your stomach).
With collaborators in Germany, I have also identified a pheromone (odiferous volatile chemical) that female Agelenopsis aperta release at maturity to advertise their availability to males. This turns out to be a very potent pheromone that might be detected at a distance of 0.1 kilometer. Females start releasing this pheromone at maturity and it continues to increase in strength until the female has mated. At this time production ceases.
Finally, I am extending this project to riparian islands throughout the desert southwest USA. Scientists are always in search of the generality of their findings. Thus, a logical question is whether this spider in other desert riparian situations experiences the same gene flow problem as the one I encountered in Portal Arizona. There is another reason for looking elsewhere. Alan Alda suggested that I was prepared to spend the next 30 years waiting for a mutation to arise in the canyon that would lead to the splitting of this single species into two entities. Because such an event may take thousands of years to occur, my visiting the site every year to look for it is not a very productive use of my time. However, there are hundreds of riparian islands in the desert southwest (three dozen in the grand canyon alone) and it is possible that a solution to the gene flow problem may have already been derived in one of these local situations. If I were to find such a discrimination mutation in one of these populations, I could introduce individuals to selected experimental locations and study the spread of the mutation (i.e.,the creation of a new species). Now that would be exciting!
Are there "timid" male spiders, and if so, have you done any studies on introducing aggressive females to timid males?
Unfortunately, we cannot pick up on what happens to timid males in the field except to note their carcasses in female boxes or successful matings. If they run off upon meeting an aggressive female, we are unlikely to see this as we can only check each female about every 45 minutes. The test you mention can be done in the laboratory and, in fact, we will be completing these laboratory trials this summer, with lab-reared individuals and another group that will be collected just before they mature.
Have you ever been bitten by a poisonous spider? We live in Arizona and see many black widows and brown recluses. Are either of these considered "aggressive"?
An interesting question because we need to distinguish between a poisonous animal and a venomous one. Baby black widows, Lactrodectus mactans, and adult males are poisonous. That is they are harmful to eat, just as many mushrooms are. Adult female black widows are not poisonous, but they are venomous. Their bites can harm people. Most spiders are venomous, rather than poisonous, but their venoms are not harmful to people. In fact, scientists are using the venoms spider produce to make drugs that help us. So far spider venoms have been found to control seizures, parathyroid problems, Alzheimer's disease and osteoporosis (loss of calcium from our teeth and bones).
I have been bitten twice in my 25 years of study of spiders. One of the bites was by a brown recluse, Loxosceles reclusa, which is known to cause skin lesions (open sores) in people. I suffered the same itching you would have after a mosquito bite. I apparently am not sensitive to the venom this spider produces.
I assume by aggressive in this question you mean towards humans. Spiders view us as an object in their environment to walk on. A spider's eyesight is so poor that it primarily detects light/dark and movement. Spiders bite people when they are squooshed in shoes or under clothing or when someone pins them onto their webs as happens when people sit on outhouse seats without checking for a black widow web first. So the answer to your question is that neither the brow recluse nor black widow are aggressive towards people. They happen to do well in man-made habitats closets, cinder blocks etc. and thus come in contact with people in unfortunate ways.
Do you perform genetic analysis of the hybrids or do you observe them for cross breeding behaviors? On the program it mentioned that you returned the spiders to the field after observing behavior and I was just wondering how you could determine which spiders were mating since there would presumably be a very large number of individuals in an your enclosure. Or do you just observe traits and assign them to their respective populations?
At this stage in my studies, I can only hypothesize that individuals that behave with a certain level of aggressiveness on a continuum from very fearful to super aggressive belong to a particular genetic class. From crossing a desert population of this species collected in central New Mexico with the Arizona creek population, I and my colleagues have developed a genetic model that explains the mechanism of inheritance of fear and aggression in this species. The two are actually separate traits that interact with one another in determining an individual's behavior. From various breeding experiments we have found that aggression is carried by the sex chromosomes while fear is on the autosomes (paired identical chromosomes). Because, we have no way of marking spiderlings in the egg case and following them through their lives (one year), we cannot distinguish the family history of individual spiders in the field. We do hope, however to use DNA fingerprinting techniques that would permit us to distinguish each individual as to which genetic type it belongs to. I am seeking the help of one of our molecular geneticists at Tennessee in applying these techniques to my canyon spiders. It may be 3-4 years before we will be able to apply this technique in the field. For now, I have to be satisfied with having each individual individually paint-marked following its collection and behavioral scoring. In this way, we can at least track individual mating success in the field relative to the behavioral attributes it has exhibited in our laboratory tests.
In the episode Spider Canyon was mentioned one curious behavioral trend in the hybrid spiders. Spiders would attack their prey despite the fact that the prey was not killed/subdued and without any visible concern for the other hunters, such as birds in the eco-system. Question: Why do these spiders behave like this in the first place? Neither of the ancestors exhibited such behavior: one was very cautious about all factors (such as sun, behavior of the ant, etc.), and the other, even though it was very aggressive, was cautious about the birds (one of the inherited traits during evolution of this particular kind of spiders). None of these behavioral trends were exhibited by the hybrid spider. Is it possible, that there was some mutation in the genes of the hybrid, which could have been caused by some external factor and not just from the genes of the "parents"?
This an excellent question but a difficult one to answer because of the understanding of complex genetic factors it requires. I'll give it a try. The strange and maladaptive behavior appears to occur because of the underlying genetic control of the two traits aggression and fear. As mentioned in the question answered just below this one, our genetic model indicates that aggression and fear are controlled by different sets of genes. In the desert populations of Agelenopsis aperta, high aggression is dominant over a high fear level. In the creek spiders, however, low fear is dominant to low aggression. If you cross the two populations then, you obtain animals that have dominant high aggression and dominant low fear. The outcome is a very aggressive batch of spiders. You are right that at some point a mutation or crossover of chromosomes would have had to occur in the creek population (not the hybrids themselves) to change the dominance relationship between fear and aggression from what is observed in the desert ancestors of these spiders.
Our class would like to know how you first became interested in working with spiders. Also, what do you like best about your work and what do you like least?
How did I first become interested in working with spiders? I have always liked animals and thus thought that I might be a veterinarian. When I entered the University of Wisconsin, I majored in zoology to obtain the biology background I would need for this career. I found that I had to take at least one field course. Field zoology involved spending fall and early winter in Wisconsin visiting streams and marshes to collect fish and other cold-blooded (ectothermic) animals that later would be identified and deposited in a museum collection. I was one of 2 girls in the class and, of course, there were no hip boots or waders that were small enough to accommodate our shoe sizes. I was always stepping out of the boots or tripping over stones in the streams and was constantly wet and cold. So I teamed up with two fellows in the class. They did the seining for fish and I followed them from along shore with the bottle to which we added our catch periodically. While waiting for the seiners to come in, I collected hundreds of spiders as these are very abundant animals in the fall. To get a decent grade in the course then, I had to identify all of these specimens to species. After spending the fall catching spiders and then looking at them under a microscope, I was hooked for life.
What do I like best about my work? Spiders are fascinating creatures. I find that working on their biology is like working on a puzzle. Each time I solve a piece of the puzzle and put it into place, several new problems show up. My work on spider biology is like a never ending story: it has taken me all over the world and into many different areas of scientific research. I started out working on physiological problems, and have added, behavior, ecology, evolution, genetics, and even biochemistry to my research areas.
What do I like least about my work? As a field biologist, I am often away from my family, friends, and pets for long periods. While the places I work often are quite spectacular and fascinating they make life for me difficult as well. For instance, I have spent as long as 7 months camped alone with my dog in one of my desert study areas. I had no running water, bathroom facilities or relief from the desert heat and I had to spend far too much time repairing tents that were torn or carried off in wind storms. In Gabon, West Africa, I had a different dilemma. Tennis shoes were best for running from angry forest elephants, but these offered no protection from driver ants which had nasty bites. The rubber boots I had to wear to keep the ants off slowed down my retreat from elephants. Because I am still here to answer your questions, you probably can guess what I wore when working on social spiders in the rainforest. While such situations might have been difficult when I was in them, I look back on each of them as having been a neat experience.
Are there more signs of divergence in the spiders' behavior or in their appearance (perhaps in ultraviolet light)?
We are unable to detect any morphological differences in the two local spider populations, woodland/aridlands, though they do have genetic differences that can be detected through DNA fingerprinting and electrophoresis. Any size differences that we are able to detect in animals collected from the woodland (hill) habitat versus the creek bed (riparian) habitat are lost in individuals reared under the same feeding levels in the laboratory. The behavioral differences between the two types remain in the common rearing environment.
With a long-term study like yours that takes place right in an animal's natural habitat, is it necessary to consider what effects you may have on the subject's behavior -- the presence of you and your researchers, the structures you've set up, removing and returning the spiders, capturing other species in the traps, etc.?
Of course, we do have to consider what effects our research activities-protocols have on our subjects' behavior and we try to minimize such effects. Spiders make great test subjects in this sense because they show no evidence of being disturbed by observation and manipulation. Agelenopsis aperta, like most spiders can see only a distance of a few centimeters. It views people as objects in its environment to walk on then rather than as some threat. The only problem that I have encountered with the study that was presented in the canyon spider story involved my use of red flags to mark web-sites. Hummingbirds glean insects off spiders webs, will take spiders if they spot them as well, and use the silk from spider webs to line their nests. One day at the research station I saw a hummingbird fly into the window of my cabin room. I puzzled over this fact and came to the conclusion that the bird was attracted to the red curtains hanging on this window (hummingbirds are attracted to red flowers which they gather nectar from). I tested losses of spider web-sites that were marked with red flags versus those marked with yellow, blue, or white flags and found that the hummingbirds were apparently attracted to my red flags. I no longer use red flags to mark web-site locations!
How long does it take to make a web to catch insects?
It takes Agelenopsis aperta approximately 2 hours to build a web. While orb weavers may eat their webs and replace them each day, the funnel-web spider has a permanent web. Thus in addition to the two hours of initial web building time, some time is spent each day adding silk to the web and repairing damage caused by insects, wind, wandering mammals, etc.
Would a hybrid spider with parents from both the desert and the river be able to live in both areas?
Hybrid animals living in the riparian habitat do not do as well as pure river spiders because they are more aggressive than even the desert spiders. As a result, they spend more time out on their web-sheets attacking prey and fighting with other spiders. While outside of its funnel, this spider makes an easy catch for a bird. Hybrids thus won't survive well in the river habitat. I have less information as to how hybrids will do in the desert habitat. I do know that hybrid desert/river individuals frequently kill each other in fights over web-sites because of their high aggressiveness. Thus many will be killed during the course of fights over territories. If hybrids survive to breed with desert or riparian spiders they further produce super fighters (the offspring of a hybrid parent and a desert parent) or super chickens (the offspring of a hybrid parent and a river parent). Super aggressive animals tend to attack all potential mates while chickens run from all potential mates. Neither type then would produce offspring to carry on their genetic lines. The answer to this question then is in the long term no.
Why is the female spider bigger than the male?
The females of many organisms are larger than males, because they put much of their body mass into the production of offspring while males only offer genetic material. Females need to be larger in size to carry large egg clutches
How many spiders are in the square you have made to do your research?
Spiders are very dense in the river area and quite sparse in the dry woodland beyond the hill. Early in the growing season of this spider, in fact, it is difficult to walk without stepping on the webs of Agelenopsis aperta in the river habitat. The enclosed area houses around 1500 spiders, most of which belong to the river population.
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