Here in Indiana we have maybe two or three short (3-4 day) periods of low humidity each summer, otherwise it is hot, sticky, muggy, moist and chewy from May to September.
On days (and nights) when the humidity is low, the bugs are nowhere to be found. Flies, mosquitos, deerflies, dragonflies, chiggers, gnats, are never around bugging you. It is especially noticiable while driving since the windshield stays clean of bug guts for days on end. As soon as the weather changes it seems like the bugs are back out in force: biting, buzzing, flying to their deaths on the windshield.
Why do the bugs hide during low humidity? Should I move to a desert to get away from these freakin’ mosquitos?
Mosquitos breed in tiny pools of water. Maybe there are more of these when the humidity is high, and therefore more mosquitos. Not sure about other insects, though maybe flies benefit from more decomposing stuff available when the humidity is high.
Another WAG - maybe flying or other activity simply tends to dry an insect out. Then during dry weather they’d be less active to avoid drying out, and humid weather would allow more activity.
Yet another WAG - maybe it also tends to be hotter during the more humid weather. Since they can’t regulate their own temperature, cooler weather would cause less activity and hotter would increase it.
I go with the humidity makes it easier to move about theory. After all, in baseball, balls are hit further and more home runs happen during the muggy summer months than the cooler months at the beginnings and ends of seasons.
Given a mass of air at, say, 20 degress with nought percent humidity and the same mass of air saturated with water vapour, it would seem to me that the latter would be more dense, that is contain a greater amount of mass per unit volume. Where’s the flaw in my logic Jonny LA?
::Off to retake GCSE physics::
This is yet another WAG to add to the list, but water loss is a major problem for insects, so I suspect those who have said that insects tend to be more active on humid days and nights to conserve their precious bodily fluids have got it right.
Insects use incredible amounts of oxygen while flying (insect flight muscle uses about 200 cubic cm of oxygen per gram per hour, more than any other known animal tissue); since they’re using so much oxygen, they have to keep their spiracles open more often in order to keep oxygen flowing to their muscles and carbon dioxide flowing out. The spiracles are one of the primary routes of water loss, and increasing the amount of time these are open will increase the rate of water loss. In dry air, about 0.9 mg of water will be lost through the spiracles for every cubic centimeter of oxygen used. More water will be lost throught the cuticle, because it is not perfectly waterproof. For every minute our insect friend decided to fly in dry air, it would have to spend at least 3 mg of water per gram of flight muscle. If water loss through the cuticle is at the same ratio as in Eleodus, a desert beetle (this is being really favorable to our insect friend, since the desert beetle is presumably well adapted to prevent water loss), then it would lose 1 mg water though the cuticle for every 0.18 mg it loses through the spiracles, then it loses an additional 16 or 17 mg of water per gram of flight muscle per minute. I don’t think there are many insects that are willing to lose 19-20 mg of water per gram of flight muscle per minute. If they just don’t fly, they’ll lose a lot less water.
If the air is humid, the rate of water loss through both the spiracles and the cuticle will be reduced depending on how humid the air is.
Whether it is easier to fly in humid air or dry air, I don’t know. I suppose that could play a role also, but I think water loss is a sufficient explanation.
All figures in this post were found in: Alexander, R. M. 1990. Animals. Cambridge Univ. Press. p. 257-263.
