#bladder flies

Most people are familiar with the relationship between spiders and flies; spiders weave webs, flies get caught and eaten. However, there are some flies that have decided to flip the script. These are aptly named the spider flies, and when the tiny larva of these species encounter a spider they crawl inside and attach themselves to the spider's lung, where they slowly feed on the spider over the next several years.

(Image: An adult Panops baudini spider fly feeding on a flower's nectar by Dan Schocknecht)