A Little Bit More
I think it’s reassuring for budding scientists to realize that most of the “good stuff” hasn’t already been discovered. Most of the “good stuff” is just waiting to be discovered and there are plenty of unknowns for everyone to unravel!
The genus of Argiope (R-gee-ope) spiders (pictured on the unit poster) is a large group of colorful spiders that are often called garden spiders. These spiders have long been known to construct stabilimentums in their webs but the function of these zig zag additions has so far eluded scientists. Although originally, studies in the 80’s seemed to point to the function of the stabilimentum as a way to provide a visual clue to prevent birds from blundering into webs, this hasn’t proven to be correct. Studies in 1999 also showed that webs with a stabilimentum actually caught 30% fewer insects when compared to spiders that did not spin a stabilimentum. Whether it’s a defensive mechanism or even an attraction to prey species remains a mystery – the answer is just waiting for someone to discover. Who knows, maybe you’ll be the one to figure this out!
Argiopes are often rather large spiders that are important predators of grasshoppers in open country habitat. Their preference for open areas in which to construct their webs frequently places them in garden and flower beds where people find them so it’s quite possible you’ve seen these colorful spiders at some time. The Black and Yellow Argiope reaches its maximum growth by the end of summer and is quite a sight as it hangs, head down, in its web. Females are much larger than males and are the ones most of us are familiar with.
Definitions
Speculate: to think about a subject
Activities
Science – Hungry Spider
Objectives: Experience how an orb-weaving spider feeds
Materials: Spider web with spider and live food
How many people have ever seen a spider capture an insect in its web and then feed on it? Although this behavior takes places millions of times each day across North America, most people have never seen it. This is a simple activity that you can participate in even if you live in a city.
CAUTION: Since this activity requires that live insects be fed to a spider, it’s probably wise to discuss this with your students before they’re involved. As always, a respectful approach to this is encouraged. Some individuals may be upset with this activity so use your discretion.
- Announce to your students that you’d like for them to see a spider in action. Ask them all to keep an eye out for an active spider web in the vicinity. They need to be sure that there is a live spider monitoring whatever web they find and then they need to avoid disturbing the web until you’re ready to try this exercise .
- Once an “active” web is found, ask them to report its location back to you. You can now inform them that you need to obtain some live food to feed the spider. This is a bit tricky since you need the selected insects to be the right size (too small or too large won’t work) and they must be alive and “kicking”.
- Once you have several live insects (you’ll want several insects to insure that at least one will “work”), you can carefully assemble around the spider web and assign one person (good to have someone who is rather dexterous) pick up the insect with hands or tweezers and toss it into the web.
- It may become immediately apparent that if anyone disturbs the web, the spider will either leave or refuse to pounce on the prey so be careful not to disturb the web in any way. Furthermore, if you choose an insect that’s too large, the spider will probably ignore the insect’s struggles or advance toward the insect and then retreat. Whatever happens, will be valuable for the students to see so be prepared for a variety of possible scenarios – no guarantees!
- If all goes as planned, you and your students should be able to watch the struggles of the insect in the web, the spider’s advance and pounce, and then either a wrap placed around the insect or an immediate feed. It’s really an impressive sight!
Some good questions to discuss after they’ve observed the spider’s behavior
- How did the spider know the insect was in its web? Most web-making spiders do not have good eyesight but they are very good at feeling any vibrations in the web. Once the spider felt vibrations from the struggling insect, it knew there was prey in its web and it knew right where it was located. This is why it’s important to have a struggling insect, not a dead one.
- We were cautioned not to have an insect that was too large. Why? Somehow a spider is able to gauge the size of its prey. If the insect is quite large, probably the spider is likely to be harmed if it tries to subdue it in the web so it simply leaves it alone. If it is too small, it may simply ignore a “snack” and wait for a meal.
- What was the spider doing when it ran up to the insect and bit it? The spider sank its fangs into the insect and injected venom into it to subdue the prey. This venom also acts on the internal organs of the insects by dissolving them. The spider can now return at its leisure and feed on the insect without any chance of being harmed itself.
- Immediately after a meal, would a second insect in the web bring the spider back for more? This might be a good question for the students and one that you could try out just to see what would happen.
Key Concepts
Structures and Functions, Predator/Prey Relationships, Identification, Behavior and Regulation
Questions
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