# Bugs and Humidity **URL:** \ **Category:** Factual Questions\ **Created:** [June 27, 2000, 1:28pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719 "2000-06-27T13:28:36Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![H8\_2\_W8](https://avatars.discourse-cdn.com/v4/letter/h/c77e96/32.png) [@H8\_2\_W8](https://boards.straightdope.com/u/H8_2_W8)\ **Post date:** [June 27, 2000, 1:28pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/1 "2000-06-27T13:28:36Z")
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? ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [June 27, 2000, 2:49pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/2 "2000-06-27T14:49:36Z")
I have absolutely no idea but here in Chicago (with very similar summers to yours) humidity seems to be a favorite time for bugs as well. As a WAG maybe humid air, being more dense, makes flight easier for the little critters. Or it could be that weather conditions that produce warm, humid air also just happen to be a bug’s ideal weather so they all go outside to party. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [June 27, 2000, 3:06pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/3 "2000-06-27T15:06:47Z")
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. ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [June 27, 2000, 8:25pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/4 "2000-06-27T20:25:04Z")
WAG and bumping this up - really like an answer. Insects don’t have lungs, maybe the humidity helps them absorb more oxygen. I’ve seen nebulisers used in hospitals and these assist breathing in some patients by increasing humidity. ---
**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\ **Post date:** [June 27, 2000, 9:17pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/5 "2000-06-27T21:17:41Z")
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. ---
**Author:** ![H8\_2\_W8](https://avatars.discourse-cdn.com/v4/letter/h/c77e96/32.png) [@H8\_2\_W8](https://boards.straightdope.com/u/H8_2_W8)\ **Post date:** [June 28, 2000, 1:26pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/6 "2000-06-28T13:26:12Z")
not a definitive answer. How do I bump this up to be considered by Cecil to get the SD? ---
**Author:** ![Montfort](https://avatars.discourse-cdn.com/v4/letter/m/d6d6ee/32.png) [@Montfort](https://boards.straightdope.com/u/Montfort)\ **Post date:** [June 28, 2000, 7:55pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/7 "2000-06-28T19:55:20Z")
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. So, Jeff\_42’s WAG sounds good to me. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [June 28, 2000, 8:04pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/8 "2000-06-28T20:04:45Z")
> [@](#): > > As a WAG maybe humid air, being more dense, makes flight easier for the little critters. Humid air is **less** dense than dry air, so it would be **harder** for them to fly in it. ---
**Author:** ![Andy](https://avatars.discourse-cdn.com/v4/letter/a/aeb1de/32.png) [@Andy](https://boards.straightdope.com/u/Andy)\ **Post date:** [June 28, 2000, 8:46pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/9 "2000-06-28T20:46:23Z")
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:: ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [June 28, 2000, 9:03pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/10 "2000-06-28T21:03:07Z")
**android** , Here is part of an article you can find at [http://www.usatoday.com/weather/wdenalt.htm](http://www.usatoday.com/weather/wdenalt.htm) > [@](#): > > **Humidity and air density** > > Most people who haven’t studied physics or chemistry find it hard to believe that humid air is lighter, or less dense, than dry air. How can the air become lighter if we add water vapor to it? > > Scientists have known this for a long time. The first was Isaac Newton, who stated that humid air is less dense than dry air in 1717 in his book, _Optics_. But, other scientists didn’t generally understand this until later in that century. > > To see why humid air is less dense than dry air, we need to turn to one of the laws of nature the Italian physicist Amadeo Avogadro discovered in the early 1800s. In simple terms, he found that a fixed volume of gas, say one cubic meter, at the same temperature and pressure, would always have the same number of molecules no matter what gas is in the container. Most beginning chemistry books explain how this works. > > What this means is that if some lighter gas molecules went into a “box” filled with a gas and the volume, temperature and pressure stayed the same, some of the heavier molecules in the box would leave. If we didn’t allow gas in the box to escape, adding more molecules of another gas would increase the pressure. Avogadro and many, many scientists after him have proved that number of molecules in the box stays the same. Adding the lighter molecules decreases the density of the gas in the box because they replace some heavier molecules. > > This is what happens when water vapor evaporates into dry air. Air is made up mostly of nitrogen molecules, which have an atomic weight of around 28, and oxygen molecules with an atomic weight of 32. Oxygen molecules consist of two oxygen atoms, which have an atomic weight of 16 each. Water molecules, which consist of one oxygen atom, atomic weight 16, plus two hydrogen atoms, atomic weight one each, have an atomic weight of 18. > > In the free atmosphere, adding water vapor to the air replaces some heavier nitrogen or oxygen molecules with lighter water molecules. Wait a minute, you might say, “I know water’s heavier than air.” True, liquid water is heavier, or more dense, than air. But, the water that makes the air humid isn’t liquid. It’s water vapor, which is a gas. > > Compared to the differences made by temperature and air pressure, humidity has a small effect on the air’s density. But, humid air is lighter than dry air at the same temperature and pressure. As a pilot, I am very aware of the effects of heat, humidity and altitude. ---
**Author:** ![wevets](https://avatars.discourse-cdn.com/v4/letter/w/e9a140/32.png) [@wevets](https://boards.straightdope.com/u/wevets)\ **Post date:** [June 28, 2000, 10:45pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/11 "2000-06-28T22:45:01Z")
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. ---
**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\ **Post date:** [June 28, 2000, 11:02pm UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/12 "2000-06-28T23:02:46Z")
Johnny L.A., that is very interesting. Thanks for posting the info! ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [June 29, 2000, 12:54am UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/13 "2000-06-29T00:54:45Z")
**zgystardst** , My pleasure… even if it _didn’t_ answer the OP! **wevets’** WAG sounds reasonable. ---
**Author:** ![Andy](https://avatars.discourse-cdn.com/v4/letter/a/aeb1de/32.png) [@Andy](https://boards.straightdope.com/u/Andy)\ **Post date:** [June 29, 2000, 2:44am UTC](https://boards.straightdope.com/t/bugs-and-humidity/23719/14 "2000-06-29T02:44:30Z")
Thanks Johnny L.A., I’d figured it out about an hour after posting. ::note to self: think before posting:: 🙂