I’m not much of a winter hiker, so during snowy months I get a nature fix from a different source: working on my growing collection of banner images. With January’s additions, the collection numbers more than 180, and you can view the whole gallery here.

At some point I want to write a blog post about the fun yet often tricky process of cropping photos into the strange shape of 596 by 175 pixels, but today I’m focusing on one image only:

This is a Weidemeyer’s admiral butterfly (Limenitis weidemeyerii), photographed on the Goshawk Ridge Trail in June 2010. This butterfly was perched only a short ways up the fire road, which was great because that day I was recovering from a bad sprain and couldn’t hobble far.

He caught my eye because he was sitting where I didn’t expect: on a drying piece of dog doo in the middle of the trail. Every time I see this photo it makes me chuckle because without looking closely at the photo, one would never notice what the butterfly is perched on.

Actually, there is a second joke in the photo: the Weidemeyer’s admiral has company on the dog doo, a smaller, orange-brown butterfly, probably a fritillary, hidden in the shadow of the larger butterfly’s wingspan. Together, the butterflies make a combined shadow on the ground that echoes the coloring on the Weidemeyer’s admiral wings—but again, without stopping to notice, one might not register that the shadow on the stones is made by two butterflies, one whose wings are open, the other’s closed.

Spotting this pair was the first time I noticed that butterflies like to hang out on dog doo. So of course it raised tons of questions: Why dog doo? What are the butterflies getting from it?

I put my questions to the experts, Jan Chu and Steve Jones, coauthors of the marvelous guidebook, Butterflies of the Colorado Front Range. They agreed: these butterflies are male. They are soaking up nutrients from the dog doo.

What kind of nutrients? Jan explained: during mating season male butterflies snack on dung to pick up minerals and proteins, which then go into forming the spermatophore, a capsule that encases each sperm. While mating, the male passes these packages of sperm and nutrients along to the female.

The day I photographed these butterflies was also the first time I’d seen a Weidemeyer’s admiral, one of the special butterfly residents of the Rocky Mountain region stretching from southern Alberta down to southern New Mexico and Arizona. They live in stream areas, where females lay their eggs on the undersides of willow leaves, sometimes also cottonwood or aspen. One fun fact about these butterflies: caterpillars may overwinter during their third stage of transformation, curling up in a tiny white sac that hangs from the bottom of a leaf and looks like a bird dropping, thus discouraging predators. The caterpillar simply hibernates during its third stage, taking a several-month-long wintry pause in its development.

Many butterflies, it turns out, prefer dung or carrion to flower nectar; for some beautiful close-up photos of butterflies on dung, see this blogger from Vancouver. For ideas on attracting dung-loving butterflies to your yard—without the dung—see this page. You can try setting out a banana peel or a bunch of compost made with cow manure. Apparently many types of rot keep these butterflies happy.

Finally, a special shout-out to my web developer, my own sweetheart, Timothy Falb, who not only put together the page of banner images but also devised a clever automated system that prevents my site from bogging down with images. Instead of loading all 180 images at once, the system randomly picks 15 at a time and changes those 15 each time the page is refreshed. (Tim programmed this whole site, for which I am grateful!)

Tim’s innovation means that I can add banner images ad infinitum. Or until winter ends. Whichever comes first.