What's on Dat Scat?

My last post addressed what kinds of insects can be found in dung, but today I want to show you what can be found on animal poop. While blow flies, family Calliphoridae, are often overwhelmingly abundant on fresh manure, you'd be surprised what else comes in for a taste.

Acmon Blue and Reakirt's Blue enjoying some refreshing scat with broad-headed bugs

Would you believe many butterflies will visit scat? Last year I happened upon this scene on a concrete nature trail in a popular park here in Colorado Springs. There were two species of gossamer-winged butterflies imbibing from some kind of predator poo. The ones with the orange bands on both the front wings and hind wings are Melissa Blues. The one with orange on the hind wing only is an Acmon Blue. The other one, without orange bands, is a Reakirt's Blue.

Melissa Blue joins Reakirt's Blue and broad-headed bugs

Males of many butterflies require mineral supplements that they can pass along to females during mating. Dung is one such mineral-rich resource.

Some butterflies feed mostly on dung, or carrion, and hardly ever visit flowers. Among them are the satyrs like this Northern Pearly-eye that was visiting dung on a bike trail in a suburb of Chicago, Illinois.

Northern Pearly-eye butterfly

The Red-spotted Purple is also notorious for preferring dung and corpses for nourishment, though one usually sees the territorial males perching on the ground or up on leaves in the canopy along stream or river corridors, or forest edges.

Red-spotted Purple butterfly

Other surprising visitors to scat are true bugs that normally feed on ripening seeds or other plant material. Finding so many broad-headed bugs, family Alydidae, sharing the poo-pile with the butterflies was quite surprising. There are at least two species here: Megalotomus quinquespinosus is the brown one, known as the "Lupine Bug." The other, smaller and blacker, is a species in the genus Alydus.

Male Golden Dung Fly

Different kind of excrement seems to attract different kinds of insects, at least to a degree. Fresh cow and horse dung is a favorite breeding ground for dung flies in the family Scathophagidae. The males stake out pats of poo and defend them from other males, while also intercepting females receptive to mating. The female lays her eggs in the manure and the larvae that hatch feed and develop there. You can easily recognize males of the Golden Dung Fly, Scathophaga stercoraria, but their fuzzy, bright golden appearance.

Various blow flies on what is probably bear scat

The blow flies (Calliphoridae) come in two basic varieties: "greenbottles" that are wholly metallic green, mostly in the genus Lucilia, and "bluebottes" that are usually larger, and gray with a metallic blue abdomen. Most of the common bluebottles are in the genus Calliphora. There is also the Black Blow Fly, Phormia regina, that is black or deep metallic blue-black. All can be present at dung.

Black scavenger fly

Tiny and wasp-waisted, black scavenger flies in the family Sepsidae are not easy to see immediately given their size, but their behavior is unmistakable: they walk around "rowing" their wings as if they needed the extra propulsion to get around.

Flesh flies of the family Sarcophagidae are gray with black "pinstripes" on the thorax, and usually red eyes and a red "tail." They are about the size of the blow flies, though some are smaller. The females "larviposit." That is, they lay tiny maggots in dung or carrion, rather than laying eggs. Bypassing the egg stage gives them a head start in exploiting the food resource.

A mating pair of flesh flies

Dung-watching is probably not going to become the next big thing in the world of naturalists, but if you can get over the "yuck factor," you might find some interesting creatures among the clean-up crew. Just make sure you are up wind.

King of the Dung Heap

Some of the most beautiful insects in the world are found under the most disgusting of circumstances. Take, for example, the subject of this week’s “Fly Day Friday.” The Golden Dung Fly, Scathophaga stercoraria, is a common species, especially in early spring and autumn. Unfortunately, it is most abundant around cow and horse manure.

The male fly, about 7-9 millimeters in length, is covered in long, bright yellow or golden hair. The insect positively glows when the sunlight strikes its body at just the right angle. Females are often smaller, and rather dull brown or gray. Males are quick to colonize a fresh heap of dung, many individuals descending on the meadow muffin. The flies are predatory on other, smaller flies that try and compete with their monopoly on the dung.

Females covet fresh scat as food for their offspring, but they first have to endure a mob of bachelors attempting to mate with them. Larger males are usually more successful at copulation than smaller individuals, but in the frenzy they sometimes mistake others of the same gender for females. Males repel such unwanted advances by pushing themselves up on their front and hind legs and kicking the would-be suitor off their back with their middle legs.

Even after mating a female is usually accosted by other males trying to “get in the last word,” so to speak. The kicker is that the female has three, sometimes four, spermathecae, internal storage chambers for sperm within her abdomen. So, not only is there external competition between male flies, but competition among their sperm, inside the female. Still, the last male to mate with a given female will fertilize about 80% of her eggs.

He often guards the female while she deposits her eggs. According to one study it takes her an average of forty-five minutes to complete oviposition. Manure that dries out, forming a crust, is nearly impossible for the flies to penetrate when laying their eggs, so there is a premium on freshness.

There is a surprisingly voluminous amount of information about the mating habits of this species, which any Google or Google Scholar search will reveal. There are even some online videos, and not all of them R-rated. The flies are easy to observe in the field, and easy to propagate in the laboratory, so they make good subjects for students and scientists, no doubt.

When not engaged in sexual behavior, or searching for poop, dung flies can be found peacefully sipping nectar from flowers, especially in early spring. I often see them on willow catkins, where they will also prey on smaller flies (see photo above). There are several generations of these insects throughout the warmer months, but they seem to be most conspicuous in spring and fall.

The Golden Dung Fly has a nearly worldwide distribution, and is not surprisingly most abundant in habitats frequented by livestock and large, wild mammals. So, forest edges, meadows, fields, farms, and ranches are good places to find them in great numbers. Not that you would want to go out looking for feces or anything….

Sources: Preston-Mafham, Rod and Ken. 1993. The Encyclopedia of Land Invertebrate Behaviour. Cambridge, Massachusetts: The MIT Press. 320 pp.
Ward, Paul I. 2000. “Cryptic Female Choice in the Yellow Dung Fly Scathophaga stercoraria,” Evolution 54(5): 1680-1686.