Compost Insects

It is the season for sharing, and eating, and if you throw the cooking and table scraps onto the compost heap you are providing a wonderful feast for a variety of insects as well. A recent visit to my in-laws in Illinois, across the Mississippi River from St. Louis, allowed me to discover a multitude of insects over the Thanksgiving holiday, thanks to their compost enclosure.

Having insect activity in your compost is a good thing. It means you have a healthy mini-ecosystem that includes decomposers which break down decaying organic matter into nutrient-rich natural fertilizer. Thus, the vegetable scraps from this year's harvest go on to feed next season's crops. Decomposers are more properly known to scientists as saprophytes, and they often require microorganisms and/or fungi to take full advantage of rotting organic debris.

Look at this yummy buffet!

I did not go digging into the already, uh....fragrant pile of material, but had I done so I certainly would have uncovered a host of invertebrates like springtails, insect larvae, millipedes, maybe woodlice, earthworms, and snails or slugs. Besides food, a compost heap offers insulation from cold weather, and even warmth given off in the process of decomposition.

Minute black scavenger fly, Coboldia fuscipes

Instead of digging and turning, I merely watched for insects appearing on the surface of the pile, or on the walls of the enclosure. These were mostly adult insects, especially flies, the larvae of which are the ones doing the work of decomposition. Chief among these were minute black scavenger flies, Coboldia fuscipes, in the family Scatopsidae. They are only 2-3 millimeters in body length, and can be mistaken for other flies of similar size.

Recently emerged adult minute black scavenger fly

I found a fair number that had just emerged from the pupal stage, with their wings in a rudimentary state awaiting full inflation. Their larvae feed in the mycelia of mushrooms, or on decaying fungal, plant, or animal tissue.

Pomace fly, Drosophila sp.

The next most abundant flies were pomace flies in the family Drosophilidae. Most people call them "fruit flies" because these are the tiny flies that hover around the overripe bananas on your kitchen counter. Indeed, they are drawn to fermenting matter where the females lay their eggs. The larvae feed mostly on the yeasts that invariably attach decaying sugars in fruits and vegetables.

Male Spotted-winged Drosophila, Drosophila suzukii

What was a little surprising was that the common pomace fly species was an exotic one: the Spotted-winged Drosophila, Drosophila suzukii. The males of this species of east Asian origin have an obvious dark spot near the tip of each wing. This fly started appearing in the northeast U.S. in 2011, and has since been recorded over most of the eastern half of the U.S. It is a known pest of a variety of fruits and berries, so it may be one of the few "bad guys" to be seen on your compost pile.

Dark-winged fungus gnat

Dark-winged fungus gnats, family Sciaridae, are abundant pretty much year round, even indoors where the larvae flourish in the soil of overwatered houseplants, feeding on roots and fungi. They are only slightly larger on average than the minute black scavenger flies.

Moth fly

Also present were moth flies in the family Psychodidae. You are probably familiar with their indoor relatives, the "drain flies" that you often see perched like tiny fuzzballs on the bathroom wall or sink basin. The larvae of moth flies enjoy eating algae, bacteria, and fungi, especially if it is exceedingly wet or sludge-like. Yum.

Male Forcipomyia sp. biting midge

Another surprise was to find an adult biting midge, probably in the genus Forcipomyia, or closely-related. Males of these tiny flies have fairly unique, bushy antennae. Depending on the species, the adult females may bite birds or mammals, or suck the blood of moths, dragonflies, and other large insects. Meanwhile, the larvae feed on algae, plant debris, or fungi.

Winter crane fly, Trichocera sp.

The largest fly I found was a winter crane fly, genus Trichocera (family Trichoceridae). It turns out the larvae of these slender, long-legged flies are scavengers on decaying leaves, vegetables, dung, fungi, and material found in rodent burrows. A few are even pests of stored tubers in your root cellar. You do have a root cellar, right?

Predatory mite

The vegetarian "bugs" also attract carnivores in the form of predatory and parasitic insects, and mites. I spotted one mite that made a cameo appearance near another insect I was photographing, but mites are typically among the most numerous of all soil-inhabiting animals. Next in line might be ants.

Japanese Pavement Ant?

I found two species of ants in and around the compost heap. Ants are difficult to identify without putting them under a microscope, but I am pretty sure these were the Japanese Pavement Ant, Tetramorium tsushimae, an Asian introduction now common around the St. Louis area and adjacent Illinois; and the Odorous House Ant, Tapinoma sessile.

Odorous House Ant

The Odorous House Ant is more of a scavenger than a predator, so it is likely to be seeking meat scraps and/or dead insects as sources of protein and fats. It is also fond of sweets.

I saw what I initially mistook for another species of ant, but it became quickly apparent it was a wingless female wasp. The ovipositor (egg-laying organ) protruding from its abdomen betrayed it as a female ichneumon wasp in the genus Gelis. So interesting is this one that you will have to wait for a separate post about it alone. Sorry!

Wingless female ichneumon wasp, Gelis sp.

Another wasp, this one fully winged, was crawling around the perimeter of the top of the wood enclosure. At this time I am unsure if it has any relationship with the compost, or is merely something that blew into the area and became too cold to fly off. I await a proper identification and will supply update this post when I have one.

Unidentified wasp

The benefits of composting to your yard and garden should be obvious, but look at what you are feeding in the meantime: an entire biosphere in miniature, pretty much. Just remember that if you're hungry, they're hungry. Bring them inside. Wait, that's not how it goes....

More Beetles from Bones

Last week I wrote about a few beetle species that I recovered from nearly dry bones here in Colorado Springs. I now have an update, plus additional species found in carrion on a recent trip to a private ranch northeast of Pueblo. It is interesting to note the succession of carrion beetle fauna over time; and the differences in diversity depending on whether the carcass is a large mammal, small mammal, bird, herp (reptiles and amphibians), or fish.

I went back to the bones I found earlier, and discovered some changes as of April 18. I spotted another Northern Carrion Beetle, Thanatophilus lapponicus, before it quickly disappeared, and more dermestids that I previously identified as Dermestes marmoratus. However, a different, smaller species was now more abundant.

Hide and Tallow Beetle, Dermestes talpinus?

I have decided I cannot readily conclude what species are involved here. Twelve species of Dermestes are recorded from Colorado, many of which look nearly identical to each other. The smaller species present on the bones appears to be the Hide and Tallow Beetle, D. talpinus. It is covered in gold or coppery scales on the pronotum (top of thorax), and silvery scales on the elytra (wing covers).

I also found a single specimen of yet another species that is possibly the Fringed Dermestid, D. frischii.

Dermestes frischii?

My wife and I travelled to Chico Basin Ranch on Monday, April 21, mostly seeking spring migrants of the feathered variety. This is a sprawling, working ranch that straddles El Paso and Pueblo Counties, and is managed for both livestock and native wildlife.

Unfortunately, one of the first birds we came across was a deceased Bobwhite quail. Turning it over revealed a shocking diversity of beetle life.

Rove beetles in the family Staphylinidae are predatory, and the ones that visit carrion feed mostly on fly maggots. They are easily recognized by the shortened elytra (wing covers), and are perhaps reminiscent of earwigs.

Hairy Rove Beetle, Creophilus maxillosus

The Hairy Rove Beetle, Creophilus maxillosus, is enormous by staphylinid standards, measuring 11-23 millimeters. These insects fly well, but quickly dig themselves out of sight when uncovered.

Rove beetle, Philonthus politus

Another rove beetle species, Philonthus politus, was also present. It is much smaller, about 10 millimeters. Special thanks to Philip Howe and Max Barclay for suggesting the genus, and Adam Brunke for volunteering the species. Facebook interest groups are a wonderful thing.

Sexton beetle, Nicrophorus sp.

Two species of the family Silphidae were also under the bird carcass: Thanatophilus lapponicus again, and one of the sexton beetles, Nicrophorus sp. Sexton beetles, also known as burying beetles, are big (11-22 mm or so), stocky, and strong. They often work in pairs to dig under the corpse of a small animal, sinking it into the ground. They then chew the carcass into a literal “meatball,” and the female then deposits a small number of eggs in a crater atop the food ball. She’ll chew up small bits of meat and feed them to her larval offspring, cleaning the food of mold and other potential contaminants in her spare time.

Clown beetle, Saprinus lugens

Clown beetles in the family Histeridae are small, spherical, highly-polished insects that play dead or dig when disturbed. They are predatory on other small insects found in carrion, dung, and other unsavory mediums. This one is Saprinus lugens, a common and widespread species measuring 5-8 mm. Thanks to Alexey Tishechkin for the species identification.

Male Scooped Scarab, Onthophagus hecate

Many dung beetles will also visit carrion, such as the little “Scooped Scarab,” Onthophagus hecate. Males have a broad, forked horn projecting over their heads from the top of the thorax. They battle each other for the right to mate with a female. At only 6-9 millimeters, O. hecate is one of the smaller dung beetles.

Hide beetle, Trox sonorae

Last but not least, were cryptic “hide beetles,” Trox sonorae, in the family Trogidae. They are closely allied to scarab beetles. Trogids are rough in texture, and usually so caked in debris as to be nearly unrecognizable as insects. They also play dead so convincingly as to be easily dismissed as living creatures. They freeze in a random, rigid posture when disturbed. This species is only 8-11 millimeters in size, which only makes it even harder to spot. Trox consume dried skin, feathers, and other material when carcasses are in the last stages of decay.

Silphid carrion beetle larva

Dermestes larva

Later in the day, Heidi and I came across the remains of a large livestock mammal, and virtually none of the beetles found on the dead quail were on this much larger vertebrate. Instead, it was carrion beetle larvae, dermestid larvae and adults, and Red-legged Ham Beetles, Necrobia rufipes. There are three common species of Necrobia, all in the family Cleridae. While most clerids are predators, Necrobia adults and larvae actually do feed on carrion, cured meats, and other dried animal products. They can be pests in museums and taxidermy businesses. Ham beetles are about 4-7 mm., but are a lovely metallic blue. They glint in the sunlight as they run over the surface of a dried corpse.

Red-legged Ham Beetle, Necrobia rufipes

Forensic entomology is the study of insects that infest dead bodies. Blow flies (family Calliphoridae) play the most prominent role in crime scene investigations because they can help ascertain the time of death. The life cycle of flies progresses in a predictable fashion, faster at higher temperatures, slower at cooler temperatures. By collecting adults, larvae, and pupae, a criminalist can determine at what time a body was first visited by ovipositing female flies.

Obviously, other insects play a critical role in decomposition as well, and beetles are chief among them. Those of you with strong stomachs may want to examine animal carcasses you come across, as the insects found there can usually be found nowhere else. Just remember to pack the hand sanitizer.