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Epic Battles 

Indoors and outside

click to enlarge glow-worm-iv_mag.jpg

Anthony Westkamper

Man vs. Fruit Fly

Confined to my house for some weeks by illness, I missed my usual walks along the Van Duzen River. Fortunately for me, there is seldom a shortage of insects wherever I go. While I was more or less bedridden, an inordinate number of tiny flying bugs invaded my home. Although I had no fruit rotting in the house, I was pretty sure they were fruit flies (Drosophila melanogaster). Tiny and tan, with ruby red eyes, they are usually drawn to rotting vegetable matter or red wine. I followed them to my currently working batch of sauerkraut. Fortunately, my crock has a water seal that prevented them from getting in and polluting the lot. I set about getting rid of them.

The best method I've found so far is to cover the bottom of a small bowl with soapsuds and stick a piece of old fruit (banana seems to work best) in the middle. The little critters try to land on the bubbles, the soap destroys the integrity of the water balance across their skin and they die in seconds. I renew the suds once or twice a day.

And a note to all you rugged outdoorspeople anxious to get out there despite the rains and drizzle, my first two brief outdoor excursions yielded half a dozen glowworms under my redwood trees at night and a tick I picked up while walking along the side of the road. Be careful when you go out — our local ticks flourish in damp weather.

Glowworm vs. Snail

One night I counted four glowworms (Pterotus intergrippinis) under my redwood trees. I have counted as many as 27 in the leaf litter beneath my small 20-foot-by-50-foot grove. The first ones I ever saw were beneath redwoods at Grizzly Creek Campground.

So far, I've seen them in every grove I've checked out on nights when the weather and moonlight were ideal. They seem to come out and display their glowing tail segments when it's dark and drippy. It is on such nights the prey to which they are particularly adapted comes out. They hunt, capture and devour small snails and slugs.

I think I've seen about all of the steps. I suspect they locate their intended prey by tracking the snail's slime trail with their short antennae. Once it catches up, the glowworm attaches its caudal appendage to the snail's shell. This gives it an anchor point from which to stretch out and bite the victim's soft body, injecting toxic saliva. The snail then reacts violently, often excreting a great mass of sticky clinging bubbles. I've been surprised that the snail didn't just withdraw into its shell as they usually do when disturbed. Instead, it stampeded (well, as much as a snail can stampede) through the tiny world of mosses and grass stems. In one case the snail actually succeed in scraping its tormentor off and escaping. I do not know if the snail survived the toxic bite but after about 10 minutes the worm did succeed in escaping the sticky clinging suds.

When the glowworm is successful, it can take up to three days to clean out the snail's shell, often glowing eerily, illuminating the hapless mollusk's shell from the inside.

This drama has played out for millions of years. The power of evolution has adapted the players through a neverending arms race. If my little grove is typical and there are about 1.6 million acres of redwoods, it means there are somewhere between 32 and 216 million Pterotus obscuripennis out there. Considering that their common name is the "Douglas fir glow worm," and there are probably many more acres of Douglas fir than redwoods, this insect may be incredibly numerous, but they are largely unseen and unknown because who goes out looking for tiny green LED-looking bugs on wet, dark, sloppy nights? Well, me.

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