Yucky but useful: Maggots make compost

I've been composting my kitchen waste for 20 years, and there's not much in the way of rotting food that can gross me out anymore. But last summer, the maggots appeared.

For years we'd had an open-air compost pile that we'd manage by layering food scraps with leaves and soil, then turning it over periodically. We saw bugs occasionally, but the turning kept them from getting too comfortable.

Then the city of Santa Cruz sold us a set of plastic, rodent-proof compost bins. The shape of the bins prevented turning of the compost, which then took ages to decompose and left layers of deoxygenated slime that stank to high heaven when you shoveled it out.

One afternoon, during a midsummer heat wave, I went to toss a bucket of food scraps into the bin. The surface of the pile was gently undulating. A carrot top appeared to be waving at me, a scrap of bread bobbed up and down. I bent in for a closer look. Big mistake.

The bin was boiling with brown and beige maggots, big leathery fellows 3/4 inch long and nearly 1/4 inch wide.

My scalp tingled, and I frantically checked my bare legs for creepy crawlies. I hurled the scraps into the bin and fled.

I didn't know what to do about this infestation, so, once my alarm subsided, I decided to do nothing. I was curious to see what would happen. If the result was unpleasant, I figured, those rodent-proof bins would be history.

Hungry, hungry maggots

Over a period of weeks I noticed a few things about my new tenants: They ate like crazy. If you tossed it in, it vanished within hours. And the compost no longer stank; it now had the mild odor of damp straw.

The maggots were very responsive; they pounced on new food and retreated from direct sunlight. You could hear them. The mass of moving larvae made a wet rustling sound, exactly like falling rain.

Yet nothing appeared to be hatching from the larvae, which had increased in number to oh, say, a billion. Oddly, the compost flies had vanished.

I became rather fond of my maggots. I took frequent breaks from the computer to watch them at work, and fretted about them when we went on vacation. I found myself saying things like, "Come and get it!" when I brought out a new load of scraps.

Vegetable peels, plate scrapings, the newspapers that lined the compost bucket - about 5 gallons of waste per week - all were gobbled up so fast that the compost pile began to recede. I tossed in squishy plums and wormy apples from our trees, 5 or 10 gallons at a time. They'd be gone by morning.

They'll eat anything

There are things you're not supposed to put in your compost pile, such as cheese, meat and oily cooked food. But I wondered what the maggots would do, so one day I cleaned out the refrigerator. My bucket was brimming with forbidden items: old sour cream, chicken parts, a wad of newspapers soaked through with bacon grease. I felt like a bad, bad gardener.

I tossed it in anyway.

An hour later I peeked in and there was a party going on. The maggots were thrashing about in a feeding frenzy. Most arresting was the fate of a fist-size ball of formerly fresh mozzarella. The maggots had tunneled into the cheese, which held its shape but quivered violently. Within a half hour it was gone.

I took my husband out to show him the action. He gazed into the mosh pit, raised an eyebrow and said, "Don't fall in!"

I decided it was time to find out if our bugs had any dodgy habits that the health department might be interested in.

Useful, native flies

A little Internet surfing revealed: Our maggots were the larvae of black soldier flies (Hermetia illucens), often referred to as BSF, a native fly whose amazing environmental usefulness is just now being explored.

While BSF have probably always lurked around my compost pile, they didn't thrive in large numbers until the rodent-proof bins prevented me from turning the pile. Mice, rats, raccoons and birds all consider BSF larvae quite delicious, and had probably picked off the ones that managed to hatch.

When kept warm and protected, BSF larvae are probably nature's best composters. They can consume the manure from factory farms, food scraps from homes and restaurants - almost any type of wet and icky organic waste.

The worst thing about falling into a vat of maggots would be the resulting nightmares: BSF can somehow tell the difference between living and nonliving tissue and eat only the dead stuff.

Because they eat so quickly, microbes can't begin to break down the waste and produce smelly methane gas, one reason why my compost stopped stinking. In addition, the larvae secrete chemicals that kill bacteria, converting even pig poop into a safe, non-smelly soil amendment, according to one study.

The lack of adult flies was because of the BSF's solitary nature. Adult flies live less than a week and don't eat. The mature larvae crawl away from the compost pile to pupate, and the flies quickly mate, lay eggs and expire.

Our other compost-loving flies had vanished because the BSF eat so fast that other flies can't get established and they are prevented from breeding. And unlike other flies, BSF are not attracted to human homes or food and do not spread disease.

Sluggish in the cold

The disadvantage of BSF larvae is that they become sluggish as the temperature drops below 68 degrees. A hard freeze will kill them, but in moderate climates they survive by burrowing deep into organic matter and going dormant until the weather warms. Commercial bug farmers (yes, there's a market) have figured out how to keep their grubs warm and happy all winter long, but my free-range population dwindled away by Thanksgiving.

I could have waited for them to reappear as spring arrived, but lacked the patience. Thank heavens for mail order!

I contacted the Phoenix Worm Store in Tifton, Ga., and within two days received 600 small BSF larvae, hungry and ready to go. The Phoenix Worm Store sells mostly to reptile owners because BSF larvae are packed with calcium, and their wriggling stimulates the reptilian appetite.

Phoenix Worm founder Craig Sheppard, a retired entomologist and expert on BSF, raises his larvae on a sterile grain-based diet. But his pampered maggots instantly burrowed into my icky compost, ate like champs and began to pupate within three weeks.

I'm now waiting for the next generation to turn my pile back into a teeming maggot buffet. My refrigerator is due for another cleaning.

Resources Contacts for maggot information and supplies: For black soldier fly larvae, go to www.phoenixworm.com. For black soldier fly information, larvae and composting supplies, go to www.thebiopod.com. For ESR International's research on bioconversion using black soldier flies, go to www.esrint.com and click on Food.