|
|
Blue Dasher's huge compund eyes are red in the female,
green in the male.Dragonflies have excellent eyesight. Their compound eyes have up to
30,000 facets, each of which is a separate light-sensing organ or
ommatidium, arranged to give nearly a 360° field of vision, important
for taking prey on the wing, as has done the female
shown above.
Odonates are completely
harmless - they do not sting or bite. Indeed, they are beneficial in the
same respect spiders and other predators are beneficial - they keep the
burgeoning insect population in check. Many of these species prey on
each other; I often see dragonflies with damsels in their clutches.
Dragonflies are among the most ancient of living creatures. Fossil
records, clearly recognizable as the ancestors of our present day
odonates, go back to Carboniferous times which means that the insects
were flying more than 300 million years ago, predating dinosaurs by over
100 million years and birds by some 150 million.
Much larger dragonfly species existed in the distant past than occur on
earth today. The largest, found as a fossil, is an extinct Protodonata
named Meganeura monyi from the Permian period, with a wingspan of 70-75
cm (27.5-29.5 in). This compares to 19 cm (7.5 in) for the largest
modern species of odonates, the Hawaiian endemic dragonfly, Anax
strenuus. The smallest modern species recorded is the libellulid
dragonfly, Nannophya pygmaea from east Asia with a wingspan of only 20
mm, or about ¾ of an inch.
Dragonflies are the world's fastest insects and, although estimates of
their speed vary wildly, most credible authorities say they are capable
of reaching speeds of between 30 and 60 km/h (19 to 38 mph). A study
showed that dragonflies can travel as much as 85 miles in one day. |
