For Scientists, Falling in Love Is a Lifetime of Research ALBUQUERQUE - Glauco Machado's plans for his future were not working out the way he had hoped. It was 1996, and he was an undergraduate in São Paulo, Brazil. He knew he wanted to be a biologist and to study amphibians with a professor who specialized in their behavior. Then the professor died in a car crash. An adviser was essential to starting a research career, but no one else at his university worked on amphibians. He was bereft. For a field biologist studying behavior, the animals that are the subjects of study may turn out to be lifelong companions. The young biologist had already given up on tortoises, his first love, because there were none nearby. Now amphibians were out. What was he to do? A friend and fellow biology student reminded him that his real interest was in studying behavior, not a specific animal, and told him about a cave with large numbers of a relatively unstudied order of arachnids (spiders, ticks, mites and other creatures that people commonly call insects, but are not), easily observed, with a wide range of behaviors. The creatures in question were harvestmen; the most familiar North American member is the daddy longlegs. As Dr. Machado, now head of the Laboratory of Arthropod Behavior and Evolution at the University of São Paulo, recalled recently, he had never heard of this group, but he was intrigued enough to go to the cave, where he encountered one small problem. "I am a little arachnophobic," he said, "a little bit." And "there were huge spiders inside the cave." For a moment he hesitated, but the harvestmen drew his gaze, some of them gathered in tangled groups of spindly legs and small bodies, others guarding nests of eggs. "They were amazing," he said. In three months he had enough information to persuade an ant specialist at the university to advise him, and to publish his first scientific paper; he had found his life's work. "It was," he said, "completely accidental." Now, a decade and a half later, Dr. Machado is one of the foremost experts on the creatures he first saw in the cave. He was at the annual meeting of the Animal Behavior Society here this month to describe the extraordinary amount of care that males in some varieties of harvestmen take of nests and eggs, and how he and his colleagues had experimentally demonstrated the reason. Within those groups, the nest-guarding males attracted more females and had more opportunities to copulate. He was an editor of the definitive work on the creatures, and the research he and colleagues in his lab have done is drawing the attention of other scientists to a once obscure group. This kind of career is often recounted by field biologists, an accidental start leading to a lifelong passion for an animal others might ignore. Although the framework of science may seem hyper-rational, some decisions are more like choosing a spouse than designing an experiment, with room for serendipity and accident. The childhood of the biologist Edward O. Wilson offers one of the best-known tales of turning an accident to good use. Dr. Wilson, among his many other achievements, is a world authority on ants. He is an author, with Berth Holldobler of "The Ants," the definitive tome on this subject, which won a Pulitzer Prize in 1991, a rare achievement for a book of serious science. But birds were his first love. He lost the sight in one eye in a childhood accident, and with it the depth perception needed to pick birds out in the forest leaves. He turned instead to close observation of the forest floor, and ants. He wrote in his autobiography, "Naturalist," that "most children go through a bug phase. I just never grew out of it. Some passions are easily understood. Jane Goodall loves chimpanzees, which she described as, "next to Homo sapiens, the most fascinating and complex in the world today." Elephants, lions, wolves and ravens have caused scientists to fall in love with them as well as study them. Other loves are more difficult for people outside of the field to grasp. Mark Siddall at the American Museum of Natural History is a great fan of the animals he studies - leeches. He told The New York Times in an article a few years ago that as a child, he hated leeches. They would attach themselves to him while he was swimming. Now he collects them all over the world. It may be that field scientists, in their professional lives, learn to love the one they're with, so to speak, or the one that will interest an adviser, and get a grant. Certainly, scientists are not trained to pick the animal that they love to study. And there is no rule that they have to stick with one animal, even if that often happens. I asked Marlene Zuk, a professor in the department of ecology, evolution and behavior at the University of Minnesota, who wrote a book about insects, "Sex on Six Legs," whether she had stayed with insects, or one variety of insect. She said that she had studied several animals, including red jungle fowl, the ancestor of chickens, and had a strong interest in birds as well as insects, but that crickets had been her main focus for many years. She said that graduate students in animal behavior are encouraged to think of what question they want to ask, not what animal they want to study. If a romance ensues, well, scientists are human. And when passionate connections are formed, they can be contagious. She said in an e-mail that because of the work of Dr. Machado and his lab, "I have developed a huge love of harvestmen." Dr. Zuk said that insects have a strong appeal to her partly because they are so different from people that it is hard to anthropomorphize them. She has stuck with crickets, she says, because "I keep finding out interesting things with them, some of them serendipitously. Also, I wanted an animal that had a sexual signal that was easy to analyze, and one that got parasites. "But," she added, "I do really like them, also."