In the summer of 1780, anti-Catholic riots led by Lord George Gordon in London left hundreds dead and stretches of the city burnt and destroyed. Eighteen months later, during a tense period in the city's history, London was invaded by brown-tail moth caterpillars. The metropolis and surrounding countryside disappeared behind the tents and nests of the insects, prompting widespread fear of famine and plague. With the memory of the riots still fresh, philanthropists such as Jonas Hanway and entomologists like William Curtis sought to assuage the public's fear, insisting that the brown-tail moth outbreak was part of the normal operations of nature, that the infestation bore no danger to the public, and that efforts to alarm the public or describe them as dangerous were contemptuous. At the same time, the conjurer and philosopher Gustavus Katterfelto, performing in the city, sought to profit from the public agitation, developing spectacles and performances that promised the insects would soon deliver famine, plague, and ruin on the city. This article examines the intersection of scientific authority, public fear, and performance, showing that the outbreak placed tremendous stress on the relationship between scientific authority and security in the metropolis.