Mosquitoes are one of my favorite venomous animals. These natural phlebotomists have efficient venoms which allow them to effortlessly violate our most precious tissue—our blood—while manipulating our immune system to remain under the radar. You can just imagine how hard that venom has to work to hide the invading mouthparts, which poke around in search of a suitable capillary, as this awesome video from KQED's Deep Look shows:
Mosquitoes don't just have a single, straw-like mouth that they insert to draw blood; instead, they have a set of needly-like parts called stylets encased in a sheath called the labium. The labium pushes up like a sleeve when the female mosquito plunges her stylets in (male mosquitoes don't bite—only the females do).
Two of the needle-like mouthparts, called maxillae, have saw-like teeth which allow her to cut through your skin to help the hunt for blood. Two others, called mandibles, keep your tissues pried open while she searches.
The main needle, which you can see flexing this way and that to find the capillary it seeks, looks like a single tube, but it's actually two stuck together: the labrum, which actually sucks the blood, and the hypopharynx, which slowly drools venom into the wound, delivering a potent chemical cocktail which increases blood flow, quiets our immune reaction, and keeps the penetrating parts oiled so they slip about with ease.
In my upcoming book Venomous, I talk a lot about mosquitoes, as well as other hematophagous (blood-eating) animals. While their dietary preferences might gross us out, they drive the selection of some really useful venoms.
After all, half of the FDA-approved, venom-derived pharmaceuticals come from bloodsuckers! Of course, that venom is also their knack for tapping into one of our most vital systems is what makes mosquitoes such good vectors for diseases like zika, malaria, and dengue. If they didn't have venom, they wouldn't be effective carriers for some of the planet's deadliest scourges.