Dermatobia
hominis (Linnaeus Jr., 1781) (Diptera: Oestridae):
Facts About Their Eggs
Dermatobia hominis females lay eggs on vectors in a specific orientation and attach them
using a very reliable adhesive.
These characteristics ensure the arthropod vector is not overly encumbered by the egg mass and
that unhatched larvae safely reach a suitable host. Cogley and Cogley
(1989) studied
the morphology of human bot fly eggs and elucidated details contributing to their low mortality rates. The eggs are approximately
1.3 mm long and whitish-yellow in color.
The ventral portion of the egg is relatively flat and has small ridges, whereas the dorsal portion has a curvature that is more
pronounced at the anterior end. The
eggs are laid side-by-side along their longitudinal axis with subsequent rows of eggs tiered one above the other. This orientation
ensures that opercula (lid-like structures) are not obstructed and thus allow larvae to readily exit the egg. Cogley and Cogley (1989) also
suggest this configuration is conservative in terms of the area needed for egg deposition.
The adhesive used by D. hominis
females to attach her eggs is also of significant import. The substance has been described as: "a varnish," "a
translucent amber," "a glue-like substance," "a chitinous substance, which hardens upon exposure to air," and "an adhesive quick-drying
cement" (see Cogley & Cogley, 1989). Regardless of the terminology used to describe the egg adhesive, the bonding
strength of this substance is extraordinary. For the sake of effect, I will quote Cogley & Cogley (1989) directly: “...the material continues
to keep eggs on carriers for at least 50 years without any obvious cracking or deterioration in its integrity…the egg mass of pinned
specimens was so firmly glued to the abdomen of stout-bodied flies that the abdomen would become detached from the thorax
before the mass would loosen” and “The fusion among eggs is so tight that the total thickness of two 4 µm chlorions side by side is
not increased beyond 8 µm.” Perhaps, we should determine the chemical composition of this cement for synthesis and use in industrial applications?
They also noted that secure adhesion is further enhanced by both egg-to-egg and egg-to-vector attachment.
You may have
been wondering whether or not these egg masses affect the flight or other activities of the vector. Well, here too, Cogley and Cogley
(1989) and Mourier and Banegas (1970) shed light on how the aerodynamic properties and configuration of D. hominis eggs
decrease the
vulnerability of the vector to predation that may otherwise be high with an unwieldy egg mass. The tiered orientation in which
D. hominis eggs are laid reduces the overall aerodynamic profile thus decreasing drag while the vector is in flight.
Lastly, the orientation of the operculum hatch line is proximal to the anterior end of the vector. Therefore, if the operculum has already
opened, air flows over it to keep it closed to protect larvae in flight until a proper host is found, and furthermore prevents air
from entering the egg which may cause desiccation and increase drag in flight.
Illustrations & Photos | Distribution | Vectors | Eggs | Myiasis | Literature
Content by Jonathan M. Eibl and Norman E. Woodley. Last Updated: August 31, 2004.
