Last weekend, I made a long recording which started on a hot summers day and ended on a much cooler night.
 
The grass was plenty wet.
 
I can't hear any impact of water on the condenser mics I was using.
 
Should I have done something to protect them? Umbrella? cellophane? I saw a video once of a guy splashing milk by a mic and he covered his mics in cellophane. Seems like it could have some negative impacts on sound though.

Dew is caused by condensation. The air has water in it and when and object  gets cool enough relative to the air around it water drops will form on it. Looking at it from that perspective there isn't much you can do except get a water proof sound transparent container. 
 
Let the mic dry out and it should be fine.   

Condenser mics are relatively sensitive to humidity. Their capacitance changes in very humid circumstances and the circuit can begin to oscillate. In a worse case scenario you can discover a high pitched whine persists until everything drys out.
 
The impedance of a condenser capsule is so high that the voltage it produces will look for alternative paths to travel towards ground. If the capsule gets a little moisture built up on the Mylar and the diaphragm ring, the electric current can crawl across the insulation and the result will be the sound of crackles and pops.
 
The capsule is polarized with a supply voltage. A 48vDC phantom system may even use a voltage step up for the capsule. The capsule is polarized at 48vDC and maybe up to 120vDC. If the moisture builds up enough you can end up shorting out the circuit and this may result in damage that requires a repair.
 
I've found myself using condenser mics (covered in thick fluffy windscreens) in the pouring rain with out failure, but it is never something that should be done casually as it could end up costing lots of money.
 
As a side note, I once worked a stage at a music festival where it rained for one set and then it got extremely humid. We were using an old monitor mixer that had global phantom power rather than specific per channel switches. We had many dynamic mics (SM58) that were seeing 48vDC and seven of those dynamic mics died do to shorting that day. Shure said they have rarely seen anything like it when they repaired them for us.
 
Moisture and microphones is not a real good combination.
 
Glad you survived and had fun with the music. :-)

Most electronics don't like to get wet. Simply placing a covering over the device is sufficient to keep the dew off. A small umbrella should work fine to keep the dew and rain off if it's absolutely necessary to record under such conditions.
 
If the equipment is warmer than the ambient air, no dew will condense on it. 
 
I recall playing a number of outside gigs and jam sessions where the gear got wet from dew. Mostly just on the top surfaces.
 
Stage mics get wet all the time.  You have cool or ambient temp mics getting breathed on by singers all the time. I remember my SM-58 being "nasty wet" during gigs both inside and outside and that mic still sounds as good as the day I bought it..... 35 years ago or more and still rocking it. A condenser or ribbon mic, on the other hand, I would not want to get wet or damp in any manner.

The Sock Monkey recommends a SOCK. 
 
All my mikes will have socks when used outdoors.
You can even order socks that fit perfectly on SM 57's and with a little black tape on a pencil condenser. Proper good quality socks do not seem to block the sound. 
I also keep the socks on my SM57's all the time. This protects them from all sorts of nasties like being dropped. It also turns them into a vocal mike. After all the biggest difference is the pop screen on a 58. 

Good way to dry out electronics that have got wet is to put them in a zip lock bag with a hand full of rice.  Leave for a day at least.
 
Works for cellphones, should work for a mic.
 
JR

Thanks everyone!!
 
To tell the truth, I'm only now realizing I packed the mics away right away. I should def put them out to make sure they dry properly. Of course they had to be packed out of the show, but now that they're home, they just reposing in the bag... I'll break them out when I get home.
 
Mike, your info was awesome as always. Very complete. Thanks!!
 
Sock Monkey, of course!! A sock is such an obvious solution. I even had a couple of pair of clean gym socks in the car I could have easily used if I'd thought of it. Next time!!
 
Guitar hacker, the dew seemed to be actually falling. I think an umbrella might have helped. When I read your post I thought of putting a light on the mics to make them apparent so people wouldn't trip on them (or tie their dog to the mic stands haha). But in this case, I don't think shining a hot light down on the Mics would have actually kept them dry.
 
Thanks for all the posts!