Species: Aedes vexans


Ae. vexans is the most common mosquito in Montana. It is widespread throughout the state and is an aggressive biter of livestock, wildlife and man. Although a few pools of Ae. vexans collected in Montana have been positive for WNV, it unlikely plays a significant role in transmission of this or other encephalitic viruses. This species is a vector of canine heartworm.


Ae. vexans is found in every state in the United States including Alaska and Hawaii. In Montana, it has been found in every county where surveillance has been conducted. During the summer and fall, females deposit eggs individually on the soil substrate in a variety of habitats (floodplains, pasture depressions, partially shaded woodland pools, roadside ditches, etc.) that have a history of flooding the following spring and summer. Larvae will hatch three to five days after flooding. Development to adult can take 10 – 30+ days depending on water temperature. Adults primarily blood feed on mammals. Analyses of blood from engorged Ae. vexans collected from Medicine Lake (Sheridan County, Mont.) showed the majority of mosquitoes had fed on deer and some on cattle (Friesen and Johnson 2013). This species overwinters in the egg stage. This is a multi-generation species with the number of generations produced related to seasonal rainfall and flood events. A late summer or early fall generation can occur when extensive rainfall results in accumulation of floodwater. As a survival strategy, only a portion of the eggs flooded will hatch; subsequent flooding will cause additional eggs to hatch. This is called installment hatching. In the absence of flooding, eggs of this species and other floodwater mosquitoes, can remain viable for several years.

Identifying Characteristics:

Abdomen pointed, narrow pale leg bands only on basal side of leg joint, pale scalloping pattern on abdominal segments.

Distribution Map:

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Mosquito and Vector Surveillance Program

MSU Extension - Department of Animal and Range Sciences

Montana State University
P.O. Box 172900
Bozeman, MT 50717-2900

Location: Marsh Labs, Room 59

Veterinary Entomology Research Associate:

Marni Rolston

Professor Emeritus of Veterinary Entomology:

Dr. Greg Johnson


Dr. Grant Hokit (Carroll College)