The Reason only Female Mosquito Sucks Blood:
The female mosquito is the only one of the Culicidae family that consumes blood because, unlike other parasitic creatures that survive exclusively on the fluids of living animals, the mosquito only uses blood as nutrition for the development of their eggs. Surviving predominantly on nectar, the female mosquito will only risk parasitic behavior because the protein and iron found in living blood will allow her to lay more eggs and yield stronger young than on a diet of nectar alone. To ensure the largest number fit offspring possible, the mosquito has evolved numerous adaptations that aid it in the location of warm blooded animals. Luckily, artificial chemicals like DEET make it possible to counter these adaptations.
Hematophagy is the animal behavior of parasitically consuming the blood of other organisms. Many insects such as ticks, lice and fleas are hematophags and survive exclusively on diets of bodily fluids drained from hosts. The female mosquito, despite what many people may believe, engages in hematophagia only for the sake of her offspring. Mosquitoes individually survive on nectar, fruit juices, and any other nutritional fluid they can sustain themselves with. All male mosquitoes have evolved without a proboscis (the needle-like appendage that a female mosquito uses to extract blood), and the females will not seek out hosts unless they have had their eggs fertilized first. A female will even develop her eggs on nectar if there are no hosts available to sustain them.
To understand why a mosquito bites, it is important to first understand evolutions naturally occurring cost/benefit calculations in species behavior. The single most important purpose of a female mosquito is to have as many of her offspring survive to sexual maturity and carry on her genetics as possible. Granted, this process on average can take little more than a week for a mosquito, but her behavior will greatly determine how many of her eggs will survive to have eggs of their own. Besides the fitness of the male whose sperm she used to fertilize her eggs, the most important contribution she will make is the amount of nutrition she can invest into her eggs to ensure as many of them hatch into healthy strong larvae as possible.
This balance between cost and benefit comes into play for the female mosquito because parasitic behavior is very dangerous and significantly decreases her chances of surviving her full lifespan. The practice of hematophagia, however, also instantly produces significantly more nutrients than the gradual accumulation and processing of plant nectar. In a single bite, a female mosquito will gorge and produce more nutrients for her eggs than she could in days of collecting nectar. It’s for this reason that a female mosquito engaging in hematophagia can, if successful, lay significantly more eggs that can hatch into stronger larvae in her lifetime than if she raised them on nectar alone. In this right, even though she risks her life by biting hosts, the rewards for surviving the venture far outweigh the risks.
The mosquito, in order to be more successful at their hematophagic strategy, has evolved an outstanding repertoire for the location of their host prey. While much of the mosquito’s hunting strategy is still a mystery, its process can be empirically broken down into two phases. The initial phase is conducted predominantly by smell. The olfactory system of the mosquito is honed to the detection of both carbon dioxide and the chemical octenol, commonly found in mammalian breath and sweat. The mosquito will initially pick up the scent of and then follow it to use the second phase: an ultraviolet sense that can detect the heat from a warm body. Because most mosquitoes are either crepuscular or nocturnal, these articulately evolved sense means they can hunt and bite without even the need of eyesight.
It’s this heavy reliance of senses besides sight that mean human chemicals such as DEET can play a major role in keeping the number of biting mosquitoes to a minimum. DEET, in combination with other chemicals, is what we find in most popular forms of bug repellant. DEET, a simple chemical that can be carried as a gaseous vapor through the air will essentially block the mosquito’s octenol receptors, making their chances of even initially detecting you far less likely. It’s for this that when you dress lightly, avoid perspiration, stay out of tall grass, don’t use any scented perfumes or hair products, and have on a layer of DEET based repellant, you can enjoy a relatively mosquito free day.