AYER — He came to visit, not to stay, but maybe he’ll be back some other day.

Such was the enigmatic nature of a temporary visitor to the mailbox of West Main Street resident Denise Krieger. She came out of her home one day last week to discover a new tenant had taken up housekeeping in what, up to then, she had assumed was restricted federal property.

“It was kind of a green and brown frog,” testified Krieger, a 20-year resident of town. “I came out to check the mail and found him living in my mailbox.”

That would have been Aug. 18 and after a short visit, the frog vacated the premises sometime by the evening of Aug. 19.

“The day we discovered there was a frog in our mailbox, the whole family went down to investigate and found that, truly, there was a frog in the mailbox.” insisted Krieger. “He was just sitting there on top of the mail. He stayed with us for almost two days before disappearing on the evening of the second day. I never had a frog in my mailbox before.”

Making the incident even more mysterious, Krieger’s mailbox is affixed to her house a good 3.5 feet off the ground. Either the frog, which was soon dubbed “FredDo,” succeeded in making an Olympic-sized leap into the inviting cavity of his federally protected home, or flew to his perch on heretofore unsuspected wings.

Alas, the explanation was likely far less fanciful.

Quite common to the New England area is the gray tree frog which has the unlikely ability to climb surfaces with few holds, even glass. Little wonder it found the rough surface of Krieger’s home less than challenging.

Not quite as large as the more common bull frog, the tree frog is medium-sized and usually comes equipped with a natural-looking light-greenish to brown-gray coloring; just as FredDo was described by Krieger.

And although Krieger said she was not cognizant of there being much in the way of croaking going on in the neighborhood of her West Main Street home (nor for that matter, in frog sightings further afield), the tree frog is known for its hearty trilling sound, the only way that it can be differentiated from other species of tree frogs that might be in the neighborhood.

Research reveals that gray tree frogs are considered “very cryptic” and are “usually hard to find,” so it’s no wonder that FredDo seemed to select the least likely of places to call home, even if only for a day.

Tree frogs are also known to prefer eating insects such as house flies, aphids, crickets, moths, termites, grasshoppers, and beetles.

It was Krieger’s theory that this diet could explain how FredDo chose her mailbox as its temporary home.

“I’m not sure what the draw was, but I think he saw our light, which we leave on all night, with all the bugs flying around it,” theorized Krieger. “I think he was a very smart frog.”

FredDo’s apparent intelligence was a factor in Krieger’s affection for the critter, prompting her not only to give him a name, but protected species status as well.

“I put up a sign on the mailbox reading ‘Please, no mail. Frogs in here!” said Krieger. “And when the mail carrier came around and saw it, he asked if it was meant as a joke. I said, ‘No, there’s a frog living in my mailbox.’ He said ‘What? What are you talking about?’ So I repeated ‘There’s a frog living in my mailbox.'”

And there FredDo remained, happily dining on delicacies of the insect world for almost two days before vanishing.

Krieger had a theory about that too, suspecting that a new mail carrier, ignoring her sign, tossed mail in the box and frightening FredDo out of his abode.

What the frog’s ultimate fate might be, Krieger could not say.

“All I know is that he hasn’t popped up anyplace else around here,” said the saddened resident.

The moral of the tale? Never disturb a frog in your mailbox if you want to control the bug population around your front door.