wasps
Explanation
The Joke
A child asks her mother, "Mommy! What are those two wasps doing?" The mother, clearly uncomfortable, launches into the standard awkward parental explanation of sex: "When two creatures love each other a whole, whole bunch, and one is a boy and one is a girl, and you know, they kinda, well, one of..." But the child interrupts: "OK, what?" The mother then explains that these are not actually the same species -- the female is ovipositing (laying eggs) into the other insect, and the larvae will eat the host insect from the inside, consuming non-vital organs first to keep it alive as long as possible.
The child's final response is simply "Please."
The Humor
The comic executes a double subversion. The setup leads us to expect the classic awkward "birds and the bees" talk, which is already a reliable source of comedy. But the mother's actual explanation is far worse than a sex talk -- she is describing parasitoid wasp behavior, one of the most horrifying reproductive strategies in nature. The child, who was presumably fine hearing about sex, is now the one who wants the conversation to stop. The humor also works because the mother was initially embarrassed about explaining something relatively innocent (mating), but then matter-of-factly delivers a description of something genuinely nightmarish without any of the same discomfort. Parasitoid wasps are famously cited in discussions of whether nature is "designed" -- even Darwin wrote that he could not reconcile a benevolent God with the existence of wasps that lay their eggs inside living caterpillars.
References
The comic references parasitoid wasps (such as those in the family Ichneumonidae), which reproduce by laying eggs inside or on other insects. The larvae consume the host from the inside, strategically eating non-vital organs first to keep the host alive longer -- a real and well-documented behavior that has long disturbed naturalists and philosophers.