Natural Enemies of Blackflies and Midges
Gastromermis
The genus Gastromermis includes important parasites of both black flies and midges. Welch (1962) described Gastromermis viridis as a parasite of Simulium vittatum. A similar mermithid occurs in Southern California. G. viridis may also be an complex of morphologically cryptic species which have yet to be clearly deferentiated. The following illustrates of some features that are characteristics of Gastromermis viridis as seen in a parasite from the mountains of Southern California. This parasite or a similar one has been found in Simulium canadensis, and S. arcticum. An undescribed species of Gastromermis has been collected from an undescribed midge in the genus Rheotanytarsis. Some unusual characteristics of this mermithid are also shown below.
Gastromermis viridis complex
Eggs
The eggs of Gastromermis viridis are attached singly to the substrate with a thin sticky substance
Preinfective larva
The infective larva of Gastromermis viridis has a long, sharp tail.
Infective Larva
The infective larva of Gastromermis viridis is characterized by a short tail. T
Adult Male
Males have a single, long, curved spicule with sharp tip. 
Adult Female
Females have a s-shaped vagina . Eggs may be seen in the vagina.
Gastromermis species from Rheotanytarsus sp.
Eggs
Clusters of eggs are embedded in gelatinous material, similar to those of snails.
Adult Male
The long, single spicule.
Adult Female
Females have a s-shaped vagina . Eggs may be seen in the uterus.
Mermithid Page
Last modified 19 December 1999