and about mosquitoes... i believe that everyone living in non-polar areas know them.
that said, i think that the relation between endurance and mosquitoes becomes quite clear: they can help us develop the third element of endurance training, mental toughness.
female mosquitoes need a daily amount of protein for the development of eggs so they suck blood from other animals. they sense carbon dioxide, so it's quite easy for them to find a living animal, human or non-human, and feed themselves. when they reach our body, they put their sting under our skin and inject a coagulating agent which brings in that area a good quantity of blood. this coagulant is exactly what makes mosquito bites so itchy (notice that once they have sucked enough blood, they suck back the same coagulating agent, so if you want to minimize the itchiness you'd better let them finish their meal and fly away spontaneously from your skin). once you've been bitten the itching will start but... if you resist a short time without touching the area (usually less than a minute) you'll avoid the coagulating agent to spread under your skin, the area of the bite won't swell and the whole trouble caused by the bite will be over. really, all it takes is resisting without scratching for a bunch of seconds. it's as easy as it sounds, still for many people it's an impossible task and mosquitoes are a big problem.
but, as said at the beginning of this post, tolerance to minor discomfort can be trained, and the same training will apply on any type of physical annoyance, be it from insects' bites or from a little blister in our foot during a marathon. there's something that technically is called cross-adaptation: we train our body to tolerate a single type of discomfort, but at the same time it learns how to deal with all type of discomfort, be it unfriendly weather, minor pain or fatigue. this is just another way to hack our body and modify its responses, and that's one more reason why mosquito bites have to be considered an opportunity to improve our standards and not a problem. plus, they live in our same environment and being able to resist to all the minor problems deriving from the environment that surrounds us will make our daily life more easy and enjoyable.
if you are an endurance athlete, it becomes even more important. just consider this: the most challenging and fascinating endurance events take place in harsh environments (think of the badwater marathon or the rovaniemi 150), and, for this type of events, adaptation to unfriendly environmental conditions has to be considered part of the training. so why not considering mosquito bites an easy way to improve our training? mosquitoes are part of the environment, and once again, it's not just the environment where we have to train and eventually compete, it's the environment in which we live daily so it's crucial that we condition our body and our mind to tolerate all its traits. and this applies to ultrarunners, couch potatoes and anyone in the middle.