Saliva and sweat are super diluted blood, they can smell that on your skin but there's no definitive proof they smell hemoglobin specifically. I found an article on the saliva and sweat and them generally being more attracted to type O blood. I think it smells good to them the way food smells good to us. I have type O blood and I get bit way more than people I'm around with different blood types. Also in my opinion it might have something to do with them being pregnant, when humans get pregnant they crave stuff depending on what vitamins their body needs and sometimes the sense of smell can get hypersensitive I kinda imagine it's the same for other land creatures that are pregnant. https://www.healthline.com/health/mosquito-blood-type#research edit: a word