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Photo of the week: A harbor seal hitches a ride on a kayak. Do you have a wildlife photo to share? Send a high resolution jpg to jmorris@bayareanewsgroup.com.

DEAR JOAN: I noticed the other day that one of the vent screens under my house had been tampered with and a very small hole had been created. I suspect something has either crawled in or out. How large of a hole do certain critters need to pass through?

Gary Cullen

Bay Area

DEAR GARY: The general rule of thumb is that if an animal can fit its head through a hole, it can get the rest of its body through.

A cat can get through an opening just 3 inches wide. A squirrel needs only 1½ inches. A raccoon can get through a space 4 inches wide. The reason this seems so improbable is that their bodies just look too darn big to fit. But that's all show -- a lot of hair or fur covering a very scrawny little body.

Mice can get in through an opening no larger than a dime.
Mice can get in through an opening no larger than a dime. (William F. Steinmetz/Philadelphia Inquirer)

Now here comes the part that could give some people nightmares. Mice need a hole only about a quarter-inch wide and young, slender rats can zip through a space as small as a half inch. We're talking the size of a dime for mice and a quarter for rats. Not all rats can fit through a space that small. Older, plumper rats need a about an inch.

Some people say rats and mice are so good at this because they can collapse their rib cages, but that's a myth. These animals simply are sleek, cylindrical creatures accustomed to navigating narrow spaces. And as with other animals, if their heads fit, their bodies will follow.

If you have a concern about visiting animals, I'd replace the screen as soon as possible.

DEAR JOAN: Several days ago, I saw a flying insect with a black, shiny, elongated body of considerable size, roughly 1½ inches long and half an inch wide; the belly side looked bulbous.

The bottom of the body was a little tilted upward. It had a head and feelers.

When it first flew near me, I really thought it was a small hummingbird. It flew into a cobweb but immediately had the strength to get out of it. I came inside.

Can you throw some light on this?

Jean Corp

Half Moon Bay

DEAR JEAN: It's very difficult to determine what type of insect you saw from just a description. The insect world is massive.

After consulting some experts, my best guess would be a tarantula hawk wasp or some sort of beetle.

Anyone else have a guess?

Home for the holidays

In the spirit of the season, South Bay animal shelters are working together on a special adoption campaign now through the end of December.

All adult pets will be adoptable for $12.

The participating shelters are City of San Jose Animal Care Center, Humane Society Silicon Valley, County of Santa Clara Animal Care and Control, Silicon Valley Animal Control Authority, Palo Alto Animal Services and Towncats of Morgan Hill.

All of the shelters are operating at maximum capacity and are counting on the community to give a pet a loving home for the holidays.

Go to www.sheltersfirst.org, the joint website for the groups, and view all of the adoptable animals.

When introducing a pet to a new home during the holidays take the time to be with them and provide a quiet place for them when things get a little too festive -- all things you should do when you have an established pet as well.

Contact Joan Morris at jmorris@bayareanewsgroup.com. Follow her at Twitter.com/AskJoanMorris.