These are tiny, almost invisible gnats. The bites usually don't itch very long, but outside of Cancun there are varieties that can be as bad as mosquitoes and even get right through screens and mosquito nets. Proper clothing and insect repellent are the only remedies. Fortunately, chakistes are quite variable depending upon season and climate conditions. The best strategy when they do swarm is to move inside. When the wind shifts or the sun moves, they tend to disappear.