Squirrels, Wolves, and Bot flies

Squirrels, Wolves, and Bot flies

Introduction:

Squirrels, wolves, and botflies represent a phenomenon of nature that is frequently not totally understood. Perhaps part of the confusion is due to the numerous species of botflies and the variation of hosts that they parasitize. This article intends to provide some clarification to that confusion.

Hunters frequently say that rabbits or squirrels like the featured image of this post are “full of wolves.” However and more accurately stated, the grotesque appearance of the pictured squirrel is due to an infestation of the parasitic larva of the botfly. Listening to the standard description and looking at the featured image, one might erroneously think that a wolf mauled the subject.  Accordingly, the pictured squirrel is suffering from a parasitic infestation of the botfly larva. 

Despite the large number of botfly species, they all do follow a general pattern of infestation with some minor variations. Typically the female botfly will deposit their eggs directly on the body of some mammal or on an intermediary vector who will later deposit the eggs on the host. Mosquitoes or houseflies are common examples of vectors that might be used.  After being deposited, the eggs will hatch and burrow into the skin where the will spend their entire larval stage of life.  Once the larva matures sufficiently, they will emerge and tumble to the ground as a pupa until they appear as a mature botfly.

Bot Fly Variations:

The botfly family of insects is represented by numerous species that follow a life pattern similar to that described above with a few variations.  Accordingly, he many species of botflies are often referred to as warble flies, heel flies or gadflies.  The deer botfly hovers near the deer’s head where she deposits the eggs in the host’s nostrils.  Once hatched, the larva migrates to the base of the tongue where they will become attached and spend the larval stage of development. 

The Deer Botfly
The Deer Botfly

One species of botflies access horses as larval hosts.  The equine botfly usually deposits its eggs on the horse’s legs. Later when the horse licks the area or brushes it with their nostrils, the eggs are transferred to the mouth and later to the intestinal tract.  There they become attached to the wall of the stomach where they remain until maturity when passed with feces.

The majority of botfly infestations, including those that afflict squirrels, rabbits and humans, are deposited as eggs to the host’s skin via another insect vector or directly.  When hatched, they will burrow into the skin and spend the larval stage of development.

Botfly Larva
This is the larva of the deer botfly.

Squirrel and Rabbit Infestations:

Squirrels and rabbits follow the typical botfly life cycle pattern.  As such the area where the larva imbeds itself produces a large lump that enlarges as the larva grows.  The feature photo, taken during mid to late summer, well illustrates the infestation.  However, it is not uncommon for the larva to still be present in game shot during hunting season.  Unfortunately, some hunters will discard the infested game, despite the fact that it poses no danger to the consumer.  Likewise the infestation poses no threat to the host.  Homeowners can observe infested squirrels through the entire period of infestation and will surely witness the squirrel’s complete recovery by mid-winter.

Photograph Attribution:

Photo of deer bot fly:
Author: Karsten Heinrich (& G. Kothe-Heinrich)
Description: Cephenemyia stimulator, Deer Botfly, Oestridae
Alterations: The only photo modification was some alterations in size.
License documentation: A copy of the GNU Free Documentation License, allowing reproduction is located at the specified link.
The author provides no endorsement related to the usage of the photograph.

Photograph of Botfly Larva:
Author: Kalumet, selbst erstellt Datum: 22.12.2005
Description:  Larval stage of the Gasterophilus intestinalis
Alterations: The only photo modification was some alterations in size.
License documentation: A copy of the GNU Free Documentation License, allowing reproduction is located at the specified link.
The author provides no endorsement related to the usage of the photograph.

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