I was thinking about presenting some of this information to younger students. The scientific criteria for classification is rather detailed.
It seems to me that younger students could benefit from simply sorting spiders into groups according to whether how/if they use webs to catch their prey .
It seems some spiders are more passive (or patient) in that they lay a web and wait for their meal to come to them. Others like the jumping spiders and wolf spiders seem to have more of a hunting instinct.
Presumably spider webs are designed to catch the most suitable prey in the most efficient manner for a given type of spider. But I wonder about the evolution of spider webs. Is it more efficient to go and look for prey, (even though this probably requires a greater energy expenditure requiring more food)
I wonder if someone would comment on the article in
which discusses the differences between 2 dimensional and 3 dimensional webs as a protective device for spiders.
Scientist Martin 7 Jul 1:25 PM
Hey Tammy: You raise some interesting questions. What evidence would you or your students accept to support the contention of which strategy; sit and wait or go looking, might be selected for?
Classifying spiders by their ecological characters might be useful for an ecologist studying feeding guilds, but can you see it does contain any information about the history of the spider taxa that construct specific web types.
Thanks for the article link. We know that the orb web evolved at least by the Jurassic (from morphological fossils not the presence of silk) and that some 3D webs evolved in spider groups that at one time also spun orb webs (2D). I find the evidence somewhat plausible, but unfortunately sphecid wasps prey on a large variety of spiders, some that make no web at all. All of which leads to the understanding that evolution really does occur in strange ways!
Tammy 9 Jul 6:45 AM
Martin asked What evidence would you or your students accept to support the contention of which strategy; sit and wait or go looking, might be selected for?
I have been thinking about this and the more I consider it the more questions come up. Before evaluating these strategies I think I would need to know a lot more ....Spiders who use webs to collect prey eat what is caught. But do they eat everything that is caught. My initial thought was to start by counting the effectiveness of the webs in catching prey as compared to the number of catches made by the hunters. BUT
1. Are some "catches" not palatable. The book talked about purse spiders netting aside a critter that was not palatable and in another spot talked about wasps with a nasty taste. So gross totals of critters captured in a web may not be valid..
2. How much can a spider eat in one day? There was a reference to spiders surviving without food for a number of days. Is this generally true of genus specific?
3. The web spider has a really good day with lots of catches. Some of them are wrapped and stored. But for how long is a stored prey edible?
4. Do all web spiders store their extra's?
Here is the scenario. Spider A caught 8 critters in its web but only three were edible.
Spider b only caught 4 creatures and 3 were edible.
Do you say they were equally effective. I wondered about the energy spent in housekeeping (getting rid of the useless catches and repairing the web.) With regard to the active hunters, How accurate are they in terms of getting edible prey. Do they spend any energy on non edible prey? My guess would be no so they could be considered the more efficient. And I do realize that the answers may vary among the many types of spiders. A second set of considerations concerns how you would go about making these observations. Spot checking the contents of a web may not give a true indication of results. What if the spider has already eaten and done its housekeeping. What looks like an empty web might be one ready for the next kill. And how do you know what a purse or funnel web spider has inside its web.
Keeping track of the diet of a jumping spider is another problem. If you are lucky to see it inaction that is one thing but how do you know what is happening the rest of the time. Do spiders have particular hunting times -- I know there are nocturnal hunters and daytime hunters but are their certain times of the day (or night ) they are more likely to be hunting.
The book talked about how spiders have split second timing in terms of pouncing. How do you know what it got since there is really no time between its targeting and eating? I am thinking of Diane Fosse spending hours just observing her gorillas. Do arachnologists spend their hours just staring at a piece of territory observing a spider? And how do you observe subterranean spiders... or those that live under the tree bark. Even those that live in leaf litter.... if you move the leaf to see the spider haven't you changed its environment?
I guess controlled experiments could be done in a lab situation but how real a setting can be setup? In terms of field work, is data collected on a rainy or just damp, or cool day significantly different from that collected on a warm or dry day. It seems to me that each condition sets up different results.
There must be spiders that hunt in the rain.... in rainforests at least.
So many things to consider. And I have lots of other ideas along this line.
Bottom line -- I have a deeper appreciation for the work arachnologists (and entimologists) do. It is one thing for me to identify a critter from an enlarged picture. Quite another thing to even see it in the wild!
I would need a web cam in my garden with an option to zoom in and record over a long stretch of time......
Paul 12 Jul 9:09 AM
Tammy, Here's a few more complications to throw into your questions:
How about determining the hunting effectiveness of web building spiders that have more than one spider in them, such as the communal web dwellers, the spiders that keep their young in their webs with them for a period of time and the pirate spider?. Is there a difference in what kind of prey the pirate spider gets versus what the spiders of a single species get? in other words, does the pirate spider get the dregs while the other spiders share more equitably?
I wonder if any of these questions could be feasibly answered in an elementary science classroom. Any suggestions on how to investigate these matters?
Luke 7 Jul 1:29 PM
There seems to be a great variety of silks used for different functions in different spiders. I suppose, after doing the reading, that the genes that carry the code for spider silk have been isolated. How many genes are involved in this process? Has a comparison been done between the sequences of various species?
Scientist Martin 7 Jul 1:41 PM
Luke: There are many genes involved as you might imagine for so complex material. Molecular biologists have isolated genes which code for about 3-4 different silk types. The proteins have, as you know been expressed in several taxa E. coli, goats etc. but we are a long way from synthesizing a composite material we would consider spider silk. I'm not sure how far along whole sequence comparisons between taxa are.