Many people look forward to summer, which brings the promise of pleasures like long days in the sun, picnics, beaches and baseball. Warm weather, however, also brings some not-so-welcome visitors in the form of stinging insects. For most people, these small creatures are an annoyance that threaten to ruin outdoor fun. But for some 2 million Americans, these insects pose a far more serious threat of a life-threatening allergic reaction.