The behaviour is a form of phoresy, and the botfly is its best-known practitioner. The female seizes a carrier insect, most often a mosquito or a muscid fly, holds it while she cements a batch of eggs to the abdomen or thorax, and lets it go apparently unharmed. Dozens of eggs may ride on a single carrier.
Hatching is triggered by the warmth of a mammal or bird when the carrier settles to feed. The emerging larva enters through the feeding puncture or a hair follicle and remains in the dermis, breathing through a pore kept open at the skin surface, for something in the region of five to ten weeks before dropping out to pupate in soil.
The arrangement solves an obvious problem. An adult botfly is conspicuous and slow, and a host that can see it will swat it, so the fly delegates the approach to an insect the host tolerates every night.