Biology of the Spotted Wing Drosophila


SWD are very similar in size, shape and appearance to other vinegar flies (i.e. our common “fruit flies”).  Adult SWD are small, 1/16 to 1/8 in long (2‐3 mm) with red eyes and a light brown thorax and abdomen. Larvae are small, legless, up to 1/8 inch long, cream colored and round in shape.


Figure 1 – SWD Male vs. Female

Photo Credits: Sheila Fitzpatrick, Agriculture & Agri-Food Canada, Pacific Agri-Food Research Center, Agassiz


Figure 2 – SWD Male vs. Female

Photo Credit: M. Hauser, CDFA

Luckily, SWD adults have certain characteristic features that help with identification.  Males have a single dark colored spot at the tip of each wing and two dark colored bands on each foreleg.  Females lack the wing spots.  Females possess a unique, serrated ovipositor (egg laying device), which distinguishes them from other vinegar flies. The serrated ovipositor is only visible with magnification.

Life Cycle

SWD adults prefer moderate temperatures and can complete a generation in as little as 8-9 days.  Adult females use their serrated ovipositor  to cut a slit into healthy fruit to deposit from one to three eggs. Several females may lay eggs on a single fruit. Eggs hatch in as little as 1-­3 days and the larvae can complete feeding within several days depending on temperature. Adults may live for several weeks and females can lay several hundred eggs in their lifetime. Because of this short generation time, buildup of large number of adults may be possible.  


Figure 3 – Life Cycle of the Spotted Wing Drosophilia

Photo Credit: Beverly Gerdeman, WSU NWREC


Figure 4 – 1 – SWD Egg on Strawberry-pale, indicated by arrow.  The two yellow objects are achenes (“seeds”).

Figure 4 – 2 – SWD Larva on Raspberry-whitish, indicated by arrow.

Photo Credits: Phil Pelliteri, UW-Madison Insect Diagnostic Lab


Figure 5 – 1, 2, 3 – Life Stage – Egg 

Photo Credits:
1 – Beverly Gerdeman, WSU NWREC
2, 3 – E. Beers, WSU


Figure 6 – Life Stage – Pupa

Photo Credit: E. Beers, WSU


Figure 7 – Life Stage – Pupa

Photo Credit: E. Beers, WSU

It is unknown how, or if, SWD can overwinter in Wisconsin. However, even if SWD does not overwinter in WI, it can be readily reintroduced each year in fruit that is shipped from warmer regions.