Home ›› 19 Dec 2022 ›› Opinion
Billions of years ago, sometime during the dinosaur era, ancient arthropods experimented with an unusual new diet: blood. Those ancestors of today’s mosquitoes, ticks and bedbugs were some of the first, but certainly not the last, to try haematophagy.
Though relatively rare as far as diets go, haematophagy – or blood-feeding – isn’t something that evolved once, or even in a small collection of closely-related animals. Haematophagy evolved independently at least 20 times in arthropods alone, as well as in a bunch of worms, some fish, and a few birds and mammals. Despite all this diversity in animal form, each coven of vampires had to tackle similar problems to refine their grisly lifestyle.
A diet as specialised as blood, a renewable but not easily accessible resource, doesn’t appear out of nowhere. Mouthparts originally used for piercing or cutting other food, like plants, gave prototype blood-feeders a head start. Many were also fortunate to live in the right place, on and around potential hosts, as scavengers, parasites, or even predators. Supported by these ‘pre-adaptations’, it was perhaps only a matter of time before some creature struck blood, discovering deep wells of untapped sustenance flowing just beneath the skin, like a Cretaceous-era oil prospector.
The nutritional benefit of blood can be clearly seen in lampreys, a group of primitive, jawless fishes with hook-adorned mouths. Lamprey species can be divided into two groups: parasitic, which feed on fish blood and flesh as juveniles, and non-parasitic, which don’t feed on blood.
“Non-parasitic lampreys are pretty much indistinguishable from parasitic lampreys as larvae, but the two types ‘part ways’ during metamorphosis [into juveniles],” says Dr Margaret Docker, an expert in lamprey biology at the University of Manitoba, Canada. Once mature, non-parasitic lampreys are “quite small… much smaller than parasitic lampreys, and even smaller than the largest larvae, since they shrink during metamorphosis.” This suggests that the nutritional benefits of blood could help the parasitic lampreys grow larger than their non-parasitic kin.
Another example of the health benefits of ‘liquid red meat’ comes from vampire moths, some of which feed on humans, and from whom blood-feeding has a clear sexual divide. The male goes through the trouble of blood-feeding, and passes on the extra sodium obtained from his blood feast to his mate as a nutritional child support.
Science Focus
