Pheromones--which Jacobs defines as chemical substances sensed by smell or taste, produced by animals in special glands, which carry information within species--are not new to children's animal books (especially re insects), but this overview of the subject per se has its own rewards. Besides their earliest discovered function as sex attractants, these powerful message systems also work to gather the clan, recruit a following, sound an alarm, mark boundaries, establish peace, or even speed or retard maturation. Jacobs further discusses how we're putting pheromones to use (mostly as insecticide substitutes), and she ends with the still open question of their existence in humans. (One intriguing bit of evidence: ""The menstrual cycles of human females living together tend to coincide."") It is to be hoped that the book's large print format doesn't put off readers who can handle Jacobs' vocabulary and writing style--it would be their loss.