The Natural Enquirer: The bot fly, part 4
A bot fly was caught and studied by the children.
The deer turned and ran, dodging this way and that, attempting to hide his head or evade the insect, but it followed him persistently. This was a robust bot fly, a heavy, swift-flying beelike insect which was now highly intent upon laying an egg or two on the deer where they would be most likely to survive, which meant in the nostrils, on his lip or on the fur at the wrists of his hooves.
She was accustomed to the frantic exertions of mammals such as this deer to get away and knew all the tricks of breaking their defenses. She employed them now. She paced the deer, biding her time, and when he briefly raised his head to look for her she arrowed in with great speed and unerring accuracy. She touched his lip just below the nose and in that instant deposited an egg there. The deer stopped and shook its head as she drove in again and this time another egg was attached to the wrist fur of his right hoof.
The deer galloped into the underbrush fringing the field and ran pell-mell into the woods, but he was no longer being pursued. Satisfied with herself, the bot fly had withdrawn and was now buzzing lazily toward a barnyard.
She alighted on a fence post a short distance from the barn and commenced cleaning her legs, wings and antennae, a procedure followed each time she had finished exerting herself to lay eggs upon some mammal. The maneuvering necessary in such a function was very tiring, she inspected the top of the fence post and found a hole just larger than her body which angled downward into the wood and which seemed an ideal place for her to rest, free from the watchful eyes of predators. She entered into the dark interior and followed the little passageway downward until it came to an abrupt dead end three inches from the opening. And here she became still and slept.
There was little doubt that those two eggs the bot fly had laid upon the deer would hatch.
The one deposited on the animal’s wrist fur would probably take somewhat longer, for it would not be stimulated until the next time he cleaned himself. As he licked the fur on his feet and legs the egg would dislodge onto his tongue and be withdrawn into his mouth and hatch there very quickly.
As for the egg deposited on his lip, chances were that it had hatched within minutes of being laid there. The female bot fly herself had been deposited as an egg similarly on the lip of a fat woodchuck last year about this time. The instant a bit of moisture had touched that egg, the fragile shell had disintegrated and she had emerged as a tiny larva almost too small to be seen. Instinctively she had squirmed toward the inner mouth. It had only taken a few minutes to reach the saliva, and subsequently she had been swallowed.
She had no eyes then so the interior darkness of the animal had not concerned her. The juices of the stomach stimulated her immediately and she clung tenaciously to the stomach wall and began to burrow. It had taken many strenuous hours of alternately burrowing and resting to make her way through the infinitesimal hole she chewed in the stomach lining.
A short time later she had began her long journey to the surface, forcing her way into muscle fibers and fatty tissues, stopping often to feed and leaving behind a little trail of partially destroyed and slightly inflamed tissue. For the most part she did not stay to feed in one place long enough to do any really serious harm to her host, but it would be some time before the woodchuck’s system could repair the minor damages she was causing.
Of this she knew nothing. Her only concern was to gorge almost continuously on the tissues through which she slowly moved. Now and again she paused for long periods to feed in one spot deep in the muscle fibers and here, each time, a small cyst would develop as the host animal’s body attempted to protect itself. It took many weeks for the larva to eat its way to the subcutaneous membranes below the woodchuck’s fur and outer skin, and here she paused a final time to feed in earnest. The point of her emergence was just in front of the woodchuck’s left hip and only an inch or so from the spine. This was among the least disturbed areas during the mammal’s daily cleansing operations, for it was one of the hardest areas for the animal to reach.
The female bot fly larva fed and grew here for quite a long time. The days became weeks and the weeks stretched into months. When she had first reached this area just under the skin of the wood chuck she was scarcely a quarter-inch long and less than a third that in diameter, but as summer dwindled into autumn and then the winter winds began to howl, she grew remarkably. By late February she was as large as she would get in her larval state and she was a decidedly ugly creature. She was now a segmented maggot an inch and a half in length and over a half-inch thick. She was an unappealing dingy gray in color and her body was essentially formless except for her head, which had grown large, sightless eyes.
The strange, rasp like mouthparts, with which she could continue to shred the muscle tissue so that the fluids could more readily be swallowed and digest, had enlarged greatly and were daily causing discomfort and damage to her host. The increase in her size had, of course, made quite a large lump on the back of the woodchuck.
To be continued…
Peter Dring is a retired nature biologist and phenologist who lives in the Land ‘O Lakes area. To comment on this story, visit the “Outdoors” section of StarJournalNOW.com.