In summer other perils take their toll. Large predatory wolf spiders, dragonflies, and killdeers pray upon and eat the small flies and their larvae. By looking closely at the microbial mats with the naked eye it is possible to find the tiny hot spring mite. No larger than a pin head they are mainly visible because of their bright vermilion color. They are structurally adapted for creeping beneath the surface film at the water's edge and for moving in open water.
Temperature controls their distribution.
When the temperature is below 113 F they move up stream. When it is above 122 F they move down stream. This behavioral adaptation assures the animals of nearly constant temperatures year round. Adults are predatory upon fly larvae and nymphs are assumed to be parasitic, but their host is not known. The hottest natural waters that fish inhabit does not exceed 104 F, although there may be fish able to tolerate water of 110 F for a few minutes.