NEW YORK (CNN/Money) - Americans young and old love Halloween. They dress up in scary or funny clothes and try to shock one another silly.

Lately, another member of the household is sticking its snout into the festivities: the family pet. Sales of costumes made especially for Fido and Muffy are flying off retail shelves.

What's more, the trend of dressing pets as Spiderman or Dracula seems to really have, well, legs. Diana Krohn, spokeswoman for BuyCostumes.com, says her company's sales of pet costumes have exploded, up 300 percent this year over last. BuyCostumes has increased its offerings to more than 40 costumes for sale on its Web site, up from just 10 in 2003.

The fad is much more popular among dog owners than people with cats. Krohn says her company sells 10 dog duds for every cat costume.

That's unsurprising. Halloween seems much more suited to the canine personality – fun loving, sociable, eager to please – than to notoriously fastidious and uncooperative felines. Cats, frankly, don't have time for such foolishness.

If you plan to dress your dog up, however, some caveats apply. Costumed canines can run into some of the same kinds of problems that small costumed kids face.

Heed this advice from the American Pet Products Manufacturing Association:

• Make sure the costume doesn't restrict breathing or vision. You don't want them running into hazards because they can't see them.
• Check to see that the outfit isn't too loose. Trailing fabric could hang a dog or cat up on a snag or fence top.
• Don't leave costumed pets unattended. They may get into unexpected trouble and need quick help to free themselves.
• If a pet resists dressing up, don't insist on it. This can stress nervous animals.

Also remember that sugary Halloween treats aren't good for your animals. So keep a tight watch on Fido to make sure he doesn't get into the trick-or-treats.