Figure 1. An antlion pit (created by Myrmeleon sp.).
© 2005 Mark Swanson
The antlion larva digs its pits in dry, sunny spots sheltered from wind and rain,
particularly on south-facing slopes. The soil must be light and easy to shift.
Pushing itself backward, the larva first draws a circle on the ground; then,
digging deeper and deeper, it spirals in toward the center. The excavated soil
is thrown out energetically with the head. After only a quarter of an hour the
antlion has made a funnel-shaped crater in the earth (Figure 1). It buries itself
at the bottom so that only the head, with opened jaws, can be seen, and there
it waits for its prey. (Grzimek 1979, 224).
The size of the crater is related not to the size of the antlion, but to its hunger; the longer the animal has gone without food, the larger it makes its crater (Grzimek 1979, 224). An interesting variable here is the effect of monthly biological rhythms: antlions dig bigger pits at full moon, with a 29.5 day cycle in isolation (Goodenough, McGuire, and Wallace 1993).
Goodenough, Judith E., B. McGuire, and R. A. Wallace. 1993. Perspectives on Animal Behavior. New York: John Wiley & Sons.
Grzimek, Bernard. 1979. Grzimek's Animal Life Encyclopedia. New York: Van Nostrand Reinhold Co.