Andrena height

It has been possible to estimate  the height of a male Andrena by using the position of its shadow projected by the sun. The assumption to be used is that the sandy soil is plane. On one occasion the male was flying over a small surface uplift with a diameter of 5 cm and a height of approximately 1 cm.

Andrena_height1

The bee does not correct its distance to the soil. From this observation it may be concluded that the bee does not use height information in this case. The male is cruising at a height of 2.6 cm until at a distance of 5 cm from the female. At 5 cm from the female the direction to the female is chosen. The inclination  is approximately 0.36. The female is already detected at a distance of 17 cm.

When the male is detecting a female while at a hole, a piece of charcoal or an other female the male will rotate in the direction of the female and fly vertically to a height of some 3 cm. Afterwards it will fly in the direction of the female with an inclination 0.15-0.5. An example is given in the following figure.

Andrena_height_from_soil

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