Science never fails to deliver on the creepy, and today's fact to try to avoid thinking too deeply about is that the tsetse fly lactates. Not only that, but its lactation can help save human lives.
Tsetse flies lactate and give milk to their young. While leaving you to contemplate that, over your cup of coffee with (hopefully) cow's cream, I'll add the even creepier fact that they express milk internally. Unlike most other flies, which lay bunches of awful eggs and give us swarms of young, tsetse flies go ahead and lay one egg, which they put in their uterus until it hatches out a larva. While inside the fly uterus, the larva drinks tsetse fly milk, expressed from special glands, and which helps its cell membranes develop until it can go out into the world.
The enzyme that helps with this development is called sphingomyelinase (SMase). SMase encoding genes are in humans as well, and a specific flaw in them causes Niemann-Pick Disease, a neurological disease that can kill, in severe cases, before age three. Although the insect and human SMase structures are slightly different, they're alike enough that modeling tsetse fly lactation and the genes involved could serve as a way to test out ways to correct the disorder in humans. This could save a lot of lives, which has to help us stomach the lactation thing.
Top Image: PLOS