Monday, 31 October 2011

The Eyes Have It

Tis the season! With onset of warm spring weather March Flies (in America Horse Flies) make their annual pesty appearance. Fortunately, their season is short but while they are on the move, they can be very annoying--especially if you are a kangaroo or wallaby. They are active by day. If you have ever thought of travelling by car throughout Alaska, you will experience these flies (and Blackflies) like never before). Australian Tabanidae comprise about 100 or more species.

The larvae of these flies breed in wet soil, along streams, in beach sand and in tree holes and the like. With the exceptional wet season and its augmentation by spring rains, it has set the stage for an exceptional year for March Flies.

This is a well studied group of flies because of their medical and veterinary importance. Livestock can be driven frantic by attacks of the flies. Most species suck blood but there are a few, as with mosquitoes, that feed on flowers. And as with mosquitoes, if you are bitten, you are bitten by the "weaker" sex. No human diseases have been transmitted by March Flies in Australia but "loaiasis" of humans (loa loa) occurs in Africa and trypanosome infections of stock is common in certain Old World countries. Anthrax can be transmitted by March Flies. Within Australia, disease transmission of a filaroid nematode is known in kangaroos and wallabies. Humans do not seem to be affected by this.
A female March Fly (Tabanidae). There is a "bridge" between the eyes of females that identifies them along with the developed mouthparts. The protruding portion, the labellum, serves as sponge to lap up the blood as it accumulates form the wound.
A male March Fly. Note that each compound eye touches the other.

March Flies seem to find their prey by sight. They are active by day but males are often found buzzing around lights. This suggests they are on the move searching for females after dark.
The compound eye consists of hundreds of facets that convey a mosaic image to the fly.

The head comprises a pair of compound eyes. Females have large numbers of facets to their eyes; males do as well but they need them to find females, not potential hosts. Females need a blood meal in order to produce a successful clutch of eggs.
A close look at one of the eyes reveals it is a myriad of individual facets.

No comments: