A spider is not an insect, although it is commonly mistaken to be an insect. Spiders, along with ticks, mites, and scorpions, belong to the class arachnida. A spider has eight legs with no visible antennae and a two-piece body. A spider has silk-spinning organs, called spinnerets, at the back end of its abdomen, and usually eight eyes of various sizes and shapes. In addition, a spider's mouth parts are different from an insect's. Instead of mandibles capable of chewing, spiders have fang-tipped jaws called chelicerae used to inject digestive enzymes into it’s prey.
Araneus diadematus, the garden spider, is a very common resident of homes and gardens. It has a distinctive white "cross" mark on the abdomen which has given rise to the alternative aliases “cross spider” and “diadem spider.” It produces the traditional orb web, characterized by a pattern of concentric circles of silk threads that are small in the center of the web and get larger towards the outer area of the web. Since the spider senses its own weight when constructing the web to determine the required amount of silk to make the web, gravity plays an important role in the construction of the web. Therefore, the objectives of this experiment were to observe how microgravity affects the weight sensing mechanism for web construction in the common cross spider.
A bag with two "brackish water" minnows known as "Mummichog Minnows" was added to the flight at the request of Scientist-Astronaut Dr. Owen K. Garriott. The objective of this experiment was to show what disorientation the fish experienced when exposed to weightlessness. The fish were flown to obtain a better understanding of the vestibular or otolith organ, which enables an animal to maintain its balance or normal orientation to the gravity force of its natural environment.
The minnows selected had to meet several fundamental requirements. They had to be small and require little or no care by the crew. Also, they had to respond quickly and consistently with regard to their vestibular function. Their vestibular system had to be similar to that of higher forms of life, and they must have been the subject of correlative studies on Earth. The obvious candidate was a small fish, the common mummichog minnow, found along the United States Atlantic coast. Two fingerlings and 50 fertile eggs were flown. The Skylab aquarium (bag) simulated a natural environment for the fish, except for gravity, by providing a dark background (bottom of pond) and a lighted surface (sky).
Spider: One day following the deployment of Arabella, a rudimentary web was constructed in the corners of the cage which was thought to be the web frame. A day later, a complete web was observed. These results prompted crewmembers to extend the original protocol by feeding the spiders rare filet mignon, providing an additional water supply, and deploying Anita at mid mission. On August 13, the Science Pilot removed half of Arabella’s existing web to initiate the construction of a new web. Arabella ingested the remaining half and refused to rebuild another web. Subsequently, water was provided where upon she proceeded to build a new web. The new web was better than the previous web indicating that Arabella had started to adapt to the microgravity environment. Arabella was returned to her launch vial and Anita was established in the cage. Anita’s reaction to the openness of the cage was recorded on video and described as being similar to Arabella's reaction, characterized as an erratic swimming motion. Both spiders died during the mission and both showed signs of dehydration which was thought to have caused their death. Examination of the returned web samples indicated that the thread spun in flight was significantly finer than that spun preflight, giving evidence that the spider utilized a weight sensing mechanism to size the thread.
Fish: After 3 days in orbit, their plastic aquarium was opened, and the fingerlings were observed to be swimming in an odd, circular pattern. The fish looped sideways, keeping their backs to the light. Loops of small radius alternated frequently with loops of larger radius. The fish swam in left loops about as much as they swam in right loops. This looping swimming decreased slowly in orbit until a normal pattern of swimming prevailed. Within 21 days, the two fingerlings appeared to have adapted to weightlessness, but they would still loop when their plastic acquarium was shaken. The eggs started hatching after 19 days, with the majority of them doing so during the fifth and sixth weeks of the mission, approximately 2 weeks after the control eggs on Earth hatched. Visual orientation was immediate upon hatching; the young fish kept their backs toward the light as their Earth-hatched cousins also did. However they also exhibited the abnormal swimming in tight circles only when the bag aquarium was shaken.
It appears that the Skylab fish utilized visual orientation, turning their backs to the light, as a substitute for gravity. Earth studies on a centrifuge have indicated that the orientation of fish is influenced both by the direction from which the light comes and the direction of the pull of gravity. In Skylab's zero gravity, the fish kept their backs to the light with no measurable deviation. The phototropic (orientation toward light) orientation and the relatively flat aquarium probably explain why they swam in loops. The fish were probably responding to signals from extremely fine hairs in their otolith which straighten out in the absence of gravity. They reacted by swimming in a forward loop which was distorted into a sideways loop by the tendency to keep their backs to the light.
|Mission||Launch/Start Date||Landing/End Date||Duration|
|Skylab 3||07/28/1973||09/25/1973||59.5 days|