Animal Magnetism
Aphid-Ranching Ants
Animal Magnetism |
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This is a close-up of the leaf stem of a
sunflower. The small dark grey insects are aphids, which feed
on the sap of the plant. The ants stimulate the aphids with
their antennæ or forelegs to excrete a substance called
honeydew which is rich in nutrients ants require. Each worker
ant goes from aphid to aphid collecting honeydew which she
stores in her abdomen until it's full, whereupon she returns to
the nest and regurgitates to feed other members of the colony.
The ants, in return, protect the aphids from predators such as
flies, wasps, and beetles.
Indeed, the arthropod contingent at Fourmilab are not entirely
unanimous regarding the use to which aphids should be put.
This ladybird (Coccinella septempunctata) is munching
away at aphids on a leaf near where the ants have their main
ranch. An ant, to the left and slightly out of
focus), is attempting (without apparent success) to harass the
beetle and chase it away.
The ants, like ranchers of our own
species, sometimes move their aphids to richer grazing grounds.
The ant ranch photo was taken by John Walker on July 6th, 2003 on the
Fourmilab grounds with an Olympus C-3040 digital camera in
macro zoom mode at f/5 and 1/100 second. The image was
cropped from the original full frame, contrast enhanced,
and slightly sharpened with
The Gimp under
Linux. The photo of the ladybird was taken on July 13th, 2003 with
the same camera and lens settings, but with automatic focus and
exposure.
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